I decided on this title half as a joke since how sure can I really be that these are really "facts". But for many years I did not know that factoids was almost a janus word, I was so used to the north american meaning of the word.

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Note how factoids are not facts in the first definition.

So below is a collection of interesting facts I came across as I read books and browsed articles online. Lot of it is from Wikipedia.

  1. Until the discovery of diamonds in Brazil in 1726, India was the only place where diamonds were mined.
  2. Below the crusts, the upper mantle while being solid rock is also ductile enough to flow very slowly under heat convection, the crusts can move on on top of the dense mantle (3.3 g/$cm^3$) and end up meeting at subduction zones. The oceanic crust being less dense (2.83 <  3 g/$cm^3$) sinks under the continental crust when they meet. Due to the heat deep inside the earth the oceanic crust partially melts back into the mantle, the lighter material rises as magma, forming volcanoes, and adds to the continental crust ensuring it stays less dense. The ocean lies on top of the oceanic crust since the continental crust (25 - 70 km) is thicker than the oceanic crust (7 - 10 km).
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The oceanic crust is young with a shorter lifecycle, it consists of mostly basalt while the continetal crust is granite. This recycling loop of the oceanic crust is why it is more dense.

3. A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. A nebular cloud the size of the Earth would have a total mass of only a few kilograms, 24 orders of magnitude less than earth. Even air taking up that much would be 21 orders of magnitude heavier. Most of them have lower pressures than the best vacuums achievable on Earth.

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Hubble's Wide Field Camera 3 observed the Carina Nebula on 24 - 30 July 2009. It is located 7500 light-years away.

4. Banded iron formations account for more than 60% of global iron reserves and provide most of the iron ore presently mined. They are distinctive units of sedimentary rock that are almost always of Precambrian age. (2.4 - 1.8 bya) They are thought to have formed in seawater as the result of oxygen production by photosynthetic cyanobacteria. The oxygen combined with dissolved iron in Earth's oceans to form insoluble iron oxides, which precipitated out, forming a thin layer on the ocean floor.

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Banded Iron Formation at the Fortescue Falls, Karijini, Australia

5. Sexual concordance refers to the degree to which genital response and self-reported sexual arousal correspond with each other. Men are significantly more sexually concordant than women. Men also are better at interoception, i.e. awareness of (nonsexual) physiological states or responses such as heart rate.

6. Around 2.45 bya, cyanobacteria (the first organisms to evolve the ability to photosynthesize) started to cause $O_2$ levels to spike (Great Oxygenation Event - peaked at 1.2 bya) leading to a mass extinction. This $O_2$ combined with methane to form carbon dioxide and water, which does not retain heat as well as methane does, leading to the oldest and longest ice age (Huronian glaciation - 2.4 to 2.1 bya).

7. In the early Universe, there were no minerals because the only elements available were hydrogen, helium, and trace amounts of lithium. Before the formation of the Solar System, there were about 12 minerals. The Great Oxygenation Event provided a new opportunity for biological and mineral diversification. It might be directly responsible for more than 2,500 of the total of about 4,500 minerals found on Earth today. Most of these new minerals were formed as hydrated and oxidized forms. Despite the natural recycling of organic matter, life had remained energetically limited until the widespread availability of oxygen. Now with greatly increased free energy available to living organisms. For example, mitochondria evolved after the GOE.

8. There have been 7 Supercontinents, with the most recent being Pangaea. With each supercontinent cycle taking 300 to 500 million years, we see the quasi-periodic aggregation and dispersal of Earth's continental crust happening. Visualize it here.

The most recent supercontinent, Pangaea, formed about 300 million years ago. See it in 3D here.

9. The Cretaceous–Tertiary (K–T) extinction event killed off some three-quarters of the plant and animal species on Earth. It was caused by the impact of a massive comet or asteroid 10 to 15 km. Every living thing with a body mass over 10 kilograms became extinct, and the age of the dinosaurs came to an end. The impact would have created a dust cloud that blocked sunlight for up to a year, inhibiting photosynthesis

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The asteroid hit an area of carbonate rock containing a large amount of combustible hydrocarbons and sulphur, much of which was vaporized, thereby injecting sulfuric acid aerosols into the stratosphere, which might have reduced sunlight reaching the Earth's surface by more than 50%, and would have caused acid rain. It would take at least ten years for such aerosols to dissipate, and would account for the extinction of plants and phytoplankton, and subsequently herbivores and their predators.

10. The Permian–Triassic (P–Tr or P–T) extinction event is the Earth's most severe known extinction event, with around 81% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It was the largest known mass extinction of insects. Some 57% of all biological families and 83% of all genera became extinct. It is thought that a large meteor impact led to the Siberian Traps Volcanic eruption (2 million square kilometres covered with lava) which led to coal or gas fires and explosions (causing dust clouds and acid aerosols, which would have blocked out sunlight and thus disrupted photosynthesis) spewed carbon dioxide (causing global warming) and spewed highly toxic ash. The warming from the greenhouse effect would reduce the solubility of oxygen in seawater, causing the concentration of oxygen to decline. The oceans became so anoxic, that anaerobic sulfur-reducing organisms dominated the chemistry of the oceans and caused massive emissions of toxic hydrogen sulfide leading to oceans euxinia.

11. The history of linguistics begins not with Plato or Aristotle, but with the Indian grammarian Panini (early to mid fourth century B. C.). Pānini's theory of morphological analysis was more advanced than any equivalent Western theory before the 20th century.

12. Kopi Luwak is also called caphe cut chon (fox-dung coffee). It is coffee that is prepared using coffee cherries that have been eaten and partly digested by the Asian palm civet, then harvested from its fecal matter. The civets digest the flesh of the coffee cherries but pass the pits (beans) inside, where stomach enzymes affect the beans, which adds to the coffee's prized aroma and flavor. 0.5 kg (1 lb) can cost up to 600 USD (₹40k) in some parts of the world and about 100 USD (₹6.6k) a cup in others.

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Coffee cherries are eaten by them and their droppings contain fermented beans. Credit - Liwa, Sumatra

13. About 66 - 68 million years ago present-day India was above the hot spot and great volumes of basaltic lava erupted to produce the Deccan Traps. As the plate moved northeast over the hot spot more volcanic centers formed: the Maldives from 55-60 million years ago, the Chagos Ridge 48 million years ago, the Mascarene Plateau 40 million years ago, and the Mauritus Islands from 18-28 million years ago. The youngest volcanoes, Piton des Neiges and Piton de la Fournaise, formed in the last 5 million years. The summits of these volcanoes make the island of Reunion. It is thought that it is also responsible for the separation of Madagascar and India.

deccan traps close up pic
The original area covered by the lava flows is estimated to have been as large as 1.5 million km^2 approximately half the size of modern India. The Deccan Traps region was reduced to its current size by erosion and plate tectonics; the present area of directly observable lava flows is around 500,000 km^2.This series of eruptions may have lasted fewer than 30,000 years. Image Source.
Made using Google Earth.

14. The north and south celestial poles are the two imaginary points in the sky where the axis of rotation, indefinitely extended, intersects the Earth. The positions of the south and north celestial poles appear to move in circles against the space-fixed backdrop of stars, completing one circuit in approximately 26,000 years. Thus, while today the star Polaris lies approximately at the north celestial pole, this will change over time, and other stars will become the "north star". In approximately 3200 years, the star Gamma Cephei will be the next north star.

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You can see how in 26,000 years it will return to Polaris. Image via Tfr000/ Wikimedia Commons.

15. If the year [ % 4 == 0 && (% 100 != 0 OR % 400 == 0) ], Then its a leap year in the Gregorian calendar. Adding that extra day bring the average length of a year to be 365.2425 which is closer to the astronomical 365.2422 days.

16. The Ancient Egyptians were the first to use 24 hours to divide the day. They divided the day into 12 hours from sunrise to sunset, and the night into a further 12 hours from sunset to sunrise.

17. When the hour was divided into 60 minutes, consisting of 60 seconds, the number 60 was probably chosen for its mathematical convenience. It is divisible by a large number of smaller numbers without a remainder: 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30.

18. Our use of the seven-day week, can be traced back to the astronomically gifted Babylonians and the decree of King Sargon I of Akkad around 2300 BCE. They certainly venerated the number seven and before telescopes the key celestial bodies numbered seven (the Sun, the Moon and the five planets visible to the naked eye). The seven-day week is closely linked to Judaism (and from the Holy Book to Christianity and Islam) based on the story of Genesis with God resting on the seventh day. For the past two millennia, Western Civilisation has had a seven-day week.

19. Regardless of the culture, all lunar months approximate the average period the Moon takes to cycle through its phases - 29 to 30 days, making a lunar year of 12 months about 11 days shorter than a solar year. There is a cycle when they align.

20. The Moon's rotation and orbital periods are tidally locked with each other, so no matter when the Moon is observed from Earth, the same hemisphere of the Moon is always seen.

If the Moon didn't spin at all, then it would alternately show its near and far sides to the Earth while moving around our planet in orbit, as shown in the figure on the right. credits

21. During a total lunar eclipse, Earth completely blocks direct sunlight from reaching the Moon. The only light reflected from the lunar surface has been refracted by Earth's atmosphere. This light appears reddish for the same reason that a sunset or sunrise does: the Rayleigh scattering of bluer light over a longer path. Due to this reddish color, a totally eclipsed Moon is sometimes called a blood moon.

22. After a little more than 18 years (Saros period), the sun, moon and earth return to the same positions. Thus eclipses of the same type repeat.

23. The Uranian axis of rotation is approximately parallel with the plane of the Solar System. It is thought that some impact event whacked Uranus into retrograde rotation unlike the remaining planets except Venus which are in prograde (anti clockwise aligned with Sun). Venus probably began with a fast prograde rotation but the strong gravitational tides trying to tidally lock Venus to the Sun caused the present-day slow retrograde rotation.

24. The spoked wheel allowed the construction of lighter and swifter vehicles. It was invented in the Harappan civilization of the Indus Valley. Chalcolithic paintings (1800-1200 BC) depict them.

25. A much more common characteristic of South Indian Hindu society is permission for marriage between cross-cousins (children of brother and sister) as they are of different gotras. Thus, a man is allowed to marry his maternal uncle's daughter or his paternal aunt's daughter, but is not allowed to marry his paternal uncle's daughter. She would be considered a parallel cousin, of the same gotra, and therefore to be treated as a sister. As much as 23% of marriages might be consanguineous in South Indian Hindu society.

Consanguineous marriage is traditional and respected in most communities of North Africa, the Middle East and West Asia, a transverse belt that runs from Pakistan and Afghanistan in the east to Morocco in the west. In South India, consanguineous marriages are culturally and socially favoured and constitute 20–50% of all marriages.

26. Sea otters spend most of their time in the water. They eat, sleep, hunt, mate and give birth in the water. To prevent themselves from floating away in the swirling sea while they sleep, sea otters often entangle themselves in forests of kelp or giant seaweed to provide anchorage. This is also the reason why they hold hands. They do so in order to prevent themselves from drifting away from the group.  The sea otter has a loose pouch of skin that extends across the chest. In this pouch (preferentially the left one), the animal stores collected food to bring to the surface. This pouch also holds a rock, unique to the otter, that is used to break open shellfish and clams.

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Sea otters, particularly mothers and pups, sometimes hold hands while floating on their backs. Hand-holding keeps the otters from drifting away from each other and their food source while they sleep.

27. On Earth, the lightning frequency is approximately 40 - 50 times a second and the average duration is 0.2 seconds made up from a number of much shorter flashes (strokes) of around 60 to 70 microseconds. Each strike causes the instantaneous release of as much as one gigajoule of energy. (The KE of 1000 1 ton vehicle moving at 161 km/h)

28. Alexander The Great had one blue and one brown eye. On either 10 or 11 June 323 BC, Alexander died aged 32, probably due to poisoning by veratrum album or calicheamicin.

29. The ability of the human brain by far exceeds what was needed for survival in the ancestral environment. One important evolutionary psychology explanation for this is that the human brain and associated traits (such as artistic ability and creativity) are the human equivalent of the peacock's tail. Superior execution of art was evolutionary important because it attracted mates.

30. By the late 19th-century, the caste system of Kerala had evolved to be the most complex to be found anywhere in India. There were over 500 groups represented in an elaborate structure of relationships and the concept of ritual pollution extended not merely to untouchability but even further, to unapproachability. Among Christians, the established Syrian Christians also practiced the rules of untouchability. Even in the 17th century, these rules were intricate - a Nair can approach but not touch a Namboodiri Brahmin: a Ezhava must remain thirty-six paces off, and a Pulayan slave ninety-six steps distant. A Ezhava must remain twelve steps away from a Nair, and a Pulayan sixty-six steps off, and a Parayan some distance farther still. The lower castes, particularly the Pulayars were not even allowed to breathe the same air as the other castes or use a public pathway. The Nair's right to kill any Pulayar (Cheraman) imminently he met on the pathway is confirmed by almost all visitors to Kerala. The demise of orthodoxy, right beliefs, has not meant the demise of orthopraxy, right practice. Caste remains endogamous.

31. The advantage metal blades have over stone ones isn’t sharpness (there was a tiny industry of stone tool manufacture for delicate eye surgery before lasers came in), but durability. Obsidian, a type of volcanic glass can produce cutting edges many times finer than even the best steel scalpels. (30 angstroms is better than the 300 to 600 angstroms of household razor blades) Obsidian scalpels older than 2100 BC have been found in a Bronze Age settlement in Turkey.

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32. It has been estimated that the observable universe contains between $10^{78}$ to $10^{82}$ atoms, far fewer than the number of possible legal positions that Go (the board game) can take when played on a regular board of size (19 x 19) which is to the order of $10^{170}$. Even for the smaller 13×13 board variant the number is around the number of atoms.

33. At the beginning of the nineteenth century an estimated three-quarters of all people alive were trapped in bondage against their will either in some form of slavery or serfdom. Most ethnic groups were slaves at one point, The Byzantine–Ottoman wars and the Ottoman wars in Europe resulted in the taking of large numbers of Christian slaves, the Romans took Britons as slaves, the Egyptians took Jews as slaves. It started way back in 1760 BC where the Code of Hammurabi condoned it.

34. Heritability is a measure of how much of the variation of a trait can be attributed to variation of genetic factors, as opposed to variation of environmental factors (given a particular environment and population). For human behavior, almost all estimates of heritability are in the moderate range of .30 to .60. Adult height - 0.80 (within families), 0.58 to 0.86 when it comes to IQ. Other traits have lower heritabilities, which indicate a relatively larger environmental influence like depression in men - 0.29, while it was 0.42 for women. But there are some controversies.

35. The word Juggernaut is derived from the Sanskrit Jagannātha (Devanagari जगन्नाथ) "world-lord", combining jagat ("world") and natha ("lord"), which is one of the names of Krishna found in the Sanskrit epics.

36. Amphibians (frogs, toads, salamanders), Annelids (earthworm) and some Echinoderms (sea urchin) breathe through their moist skin.

37. Moment magnitude (Mw) is now the most common measure of earthquake size for medium to large earthquake but much of the news media still refers to these as "Richter" magnitudes. But the United States Geological Survey does not use this scale for earthquakes with a magnitude of less than 3.5.

38. The northern lights or auroras are the result of disturbances in the magnetosphere caused by solar wind. They take place on an 11-year solar cycle, it is inversely affected by the sun spot cycle. The last solar minimum (few sunspots appear on Sun's surface) occurred in December 2019, marking the start of a new solar cycle. It is expected that July 2025 is the next solar maximum and that is when we can expect the northern lights to shine brightly again.

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The Aurora borealis, or northern lights, above Bear Lake, Alaska

39. Sugarcane is the world's largest crop by production quantity, global production of sugarcane in 2018 was 1.91 billion tonnes, with Brazil producing 39% of the world total, India with 20%, and China and Thailand producing about 6% each. Sugarcane accounts for 80% of sugar produced.

40. As of 2019, over 75% of cocoa produced worldwide comes from West Africa, specifically Côte D'Ivoire, Ghana, Cameroon and Nigeria. Côte D'Ivoire alone produces more than 40% of cocoa beans grown throughout the world. Chocolate might contain 30 or more insect parts and a sprinkling of rodent hair. Cockroach parts are also inevitable. At different stages of the process there is always risk of insects making its way into the chocolate, the beans are fermentated, dryed, roasted, grounded then blended with sugar. Insects are nutritious and using pesticides to stop them would actually harm us.

41. Birth rate is inversely correlated to education and income while positively to religion.

42. So every two or three years (on average about once every 2.7 years - seven times in the 19 year Metonic cycle - a period of approximately 19 years after which the phases of the moon recur on the same day of the year), there is an extra full moon in the year. The extra full moon necessarily falls in one of the four seasons, giving that season four full moons instead of the usual three, and, hence, a "blue" moon. The term "blue moon" is used colloquially to mean a rare event, as in the phrase "once in a blue moon".

43. Around 10 percent of lifelong smokers will get lung cancer. While smoking accounts for 30 percent of all cancer deaths and 80 percent of lung cancer deaths. People who smoke cigarettes are 15 to 30 times more likely to get lung cancer or die from lung cancer than people who do not smoke. Half of all smokers will die from smoking.

44. The soil in China lacked selenium, a deficiency which contributed to muscular weakness and reduced growth in horses. Consequently, horses in China were too frail to support the weight of a Chinese soldier. The Chinese needed the superior horses that nomads bred on the Eurasian steppes, and nomads wanted things only agricultural societies produced, such as grain and silk. Thus the Silk route was born out of the silk-for-horses trade.

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The Silk Road trade played a significant role in the development of the civilizations of China, Korea, Japan, the Indian subcontinent, Iran, Europe, the Horn of Africa and Arabia, opening long-distance political and economic relations between the civilizations.

45. Thailand mainly uses the Buddhist calendar which is 543 years ahead of the Gregorian calendar. The year 2018 CE is indicated as 2561 BE in Thailand. The first day of the week in Thailand is Sunday.

46. The high cost of failing to detect agents and the low cost of wrongly detecting them has led researchers to suggest that people possess a Hyperactive Agent Detection Device, a cognitive module that readily ascribes events in the environment to the behavior of agents.

47. Humans have a slightly over 210-degree (depth perception is possible only in 114 degrees) forward-facing horizontal arc of their visual field. The vertical range of the visual field in humans is around 150 degrees.

48. Westermarck effect or reverse sexual imprinting says that where a brother and sister are brought up separately, never meeting one another - they may find one another highly sexually attractive when they meet as adults or adolescents. Also people who live in close domestic proximity during the first few years of their lives become desensitized to sexual attraction.

49. Men and women are likely to choose a partner with the same eye color as the parent of the sex they are attracted to. This effect seems to be affected by the kind of relationship they had with that parent. Similar effects are seen in other animals.

50. Mechanically speaking, our eyes see everything upside down. That’s because the process of refraction through a convex lens causes the image to be flipped, so when the image hits your retina, it’s completely inverted. We don't know if babies are born with this ability but adult humans have been able to demonstrate the ability to adapt. Wear a set of reversing glasses to flip your vision upside down, and by day five, it will have spontaneously turned up side down.

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Rays from the top and bottom of the object are traced and produce an inverted real image on the retina.

51. Since light rays from a nearby object can diverge and still enter the eye, the lens must be more converging (more powerful) for close vision than for distant vision. To be more converging, the lens is made thicker by the action of the ciliary muscle surrounding it. The eye is most relaxed when viewing distant objects, one reason that microscopes and telescopes are designed to produce distant images. Vision of very distant objects is called totally relaxed, with the closest vision being  fully accommodated. Modern human lifestyle involves looking at nearby objects for long periods of time. We need to take breaks and look into the distance so that the eye can relax.

52. The image that hits each of your retinas is a flat, 2D projection. Your brain has to overlay these two images dynamically to form one seamless 3D image in your mind. At the periphery of your vision, you pretty much only see in black and white. The brain fills in the 1.5 mm blind spot (where the optic nerve passes through the optic disc).

53. The late teens or early twenties is the best time biologically (oocytes are fresh, lowest rates of miscarriage, ectopic pregnancy, stillbirth, and infertility) speaking to have kids but with how society is progressing, this is getting out of sync with the the sociological "best age", humans usually mature a decade later around 25 to 35 but that depends on the  individual.

54. The plank length is a sort of natural unit of length, using generalized uncertainity principle it could also be the minimal length that can be resolved - $1.6 \times 10^{-35}$ m (note that $0.84 \times 10^{-15}$ m is the diameter of a proton). At that level of precision you only need 62 digits of pi to calculate the circumference of the universe.

55. When Leibnitz first came up with the notation for integrals (the ∫ sign was really a capital S, standing for "summa" or summation), and he wrote $S^b_a f(x)dx$, he was really thinking of this as a sum of products, with dx representing an "infinitesimal change in x.

56. For adults 18 and older, a normal resting heart rate is between 60 and 100 beats per minute (bpm). So a heartbeat every 1 to 1.6 second makes the second a very intuitive unit of time. (Our ancestors must have had a lower resting heart rate compared to us due to their healthier lifestyle.

57. In fact, economists estimate that only 8 percent of the world's currency exists as physical cash. The rest exists only on a computer hard drive, in electronic bank accounts around the world.

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You had to scroll a lot, I am sorry but I hope it was worth it. Credit to Visual Capital.

58. About 1 in 5 Sun-like stars have an "Earth-sized" planet in the habitable zone. Assuming there are 200 billion stars in the Milky Way, one can hypothesize that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included. 6 billion is a more recent estimate.

59. Even in individuals who were born blind, body and facial expressions displayed are similar to those of anyone else.

60. Under stress, a human brain will shift control from the cerebral cortex to the limbic system. The limbic system is associated with the instinctual processes, such as "fight or flight" response; and behavior that is based on "deeply ingrained training". The limited input from the cerebral cortex hinders a person's creative processes, which are replaced by the behaviors associated with the limbic system. The person is often unaware of the change, which may lead them to believe they are creatively "blocked".

61. Auditory feedback (AF) is an aid used by humans to control speech production but it is a slow correction mechanism since taking 100 milliseconds before correction is usually too slow in comparison to the production time of speech sounds. For comparison visual feedback for movement control takes 135 milliseconds. While auditory feedback is too slow to correct the production of a speech sound in real time. It is capable of changing speech-sound production over a series of trials (i.e. adaptation by relearning - 10 minutes is typically sufficient for a nearly-full adaptation). Speech Jammers playback your speech with a delay of about 0.2 seconds which confuses the trained brain.

62. Traditionally, in the Middle Ages, an acre was defined as the area of land that could be ploughed in one day by a yoke of oxen. Precisely it is 43,560 square feet

63. In wires (say copper wires), electrons travel at maybe 0.023 mm/sec. Even in vacuum tubes (space) they only travel around 1% of the speed of light. What really matters in circuits is the energy and information that are carried by fluctuations in the electromagnetic field, which travels near the speed of light.

64. Because the Earth was molten when it was formed, almost all of the gold present in the early Earth probably sank into the planetary core. Therefore, most of the gold that is in the Earth's crust and mantle is thought to have been delivered to Earth later, by asteroid impacts during the Late Heavy Bombardment, about 4 billion years ago.

65. Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms. The smallest current we can feel is 1 mA in one second of contact. Above 100 mA can cause real damage. So 1000 Volts is where usually the danger lies.

66. The retina can respond to a single photon, but neural filters only allow a signal to pass to the brain to trigger a conscious response when at least about five to nine arrive within less than 100 ms. Our cone cells detect those photons with wavelength in the range of about 380 to 720 nanometres (visible light). There is no intrinsic limit to the smallest or farthest thing we can see. The best we can do is resolve a line pair at 0.94 arc minutes (about a fingernail held at arm's length with 60 horizontal and vertical lines)

67. Comparing the size of our neocortex to other primates and the sizes of the groups in which they dwell suggests the natural size of a human group is around 150 people. Gossip plays an important role in making this possible. Cooperation in numbers beyond that needs commonly believed fictions.

68. The unit for loudness - dB or decibel (one tenth of a bel (B)) originates from methods used to quantify reductions in audio levels in telephone circuits. These losses were originally measured in units of Miles of Standard Cable (MSC), where 1 MSC corresponded to the loss of power over a 1 mile (approximately 1.6 km) length of standard telephone cable at a frequency of 5000 rad/sec, this roughly matched the smallest attenuation detectable to the average listener. 1 TU ($ 10 \log_{10} \frac{P_{measured}}{P_{reference}}$) approximately equaled 1 MSC (specifically, 1.056 TU = 1 MSC). In 1928, the Bell system renamed the TU into the decibel. We use a logarithmic scale because of how our senses work, the human perception of the intensity of sound and light approximates the logarithm of intensity rather than a linear relationship (Weber–Fechner law).

69. Our ears do not have a flat frequency response. The hearing curves show a significant increase in the range 2000 - 5000 Hz with a peak sensitivity around 3500 - 4000 Hz. This is associated with the resonance of the auditory canal. There is another enhanced sensitivity region at about 13,500 Hz which may be associated with the third harmonic resonance of the auditory canal. The high sensitivity region at 2-5 kHz is very important for the understanding of speech.

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We humans have different levels of senstivity depending on loudness (colored lines show equal sound pressure levels) and frequency (x axis)

70. Godel has showed that incompleteness is an intrinsic feature of mathematical systems: any logic powerful enough to include arithmetic statements will necessarily contain true propositions that are neither provable nor disprovable.

71. The vast majority of money (97%) comes into being when a commercial bank extends a loan. Banks create deposits in their act of lending. This because Fractional Reserve Banking lets banks lend all but a fraction of their deposits. Now both the deposits and the loan amount can act as real money. But banks can also borrow from other banks so they look to look for reserves to partly (8% to 10%) back the loan after they make the loan.

72. For life to exist, planets seem to need a non-uniform energy input, atmosphere, and water. These came into existence by time the Universe is just 300 million years old. By time we arrive at the formation of Earth more than 9 billion years have passed. High metalicity is also indicating that we should have seen the first earth like planet 1 - 3 billion years after the big bang.

73. Special relativity forbids the propagation of information faster than the speed of light. In a wave, the group velocity carries all the information. The phase velocity can and often is (imagine x-rays passing through glass) faster than the speed of light, as it carries no information. The refractive index is defined as the ratio between the speed of light in a vacuum and the phase velocity in a medium, so it can be less than one. It can be complex, in case of metamaterials, it can even be negative!

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Above we can see frequency dispersion in waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. The red square moves with the phase velocity, and the green circles propagate with the group velocity. In this deep-water case, the phase velocity is twice the group velocity. The red square overtakes two green circles when moving from the left to the right of the figure.

74. A typical neuron can fire and reset itself in about five milliseconds (5 ms), or around two hundred times per second. It seems unlikely that the average cortical neuron spikes much more than once per second. This may seem fast, but a modern silicon-based computer can do hundreds of billion operations in a second. This means a basic computer operation is five hundred million times faster than the basic operation in your brain.

75. A tiny variety of jellyfish known as Turritopsis doohmii, or more commonly, the immortal jellyfish. It has found a way to cheat death by actually reversing its aging process. If the jellyfish is injured or sick (under the conditions of starvation, sudden temperature change, reduction of salinity, and artificial damage), it returns to its polyp stage over a three-day period, transforming its cells into a younger state that will eventually grow into adulthood all over again.

76. Planarian worms are famous for their regeneration abilities, a worm cut across or lengthwise can form two separate worms. This apparently limitless regeneration also applies to aging and damaged tissue, allowing the worms to cheat death indefinitely.

77. Green monkeys can lie. They have been observed to frighten away fellow monkeys by claiming a lion is nearby in order to steal a banana for itself. Other animals lie too.

78. Humans have hair not fur, which let the sweat freely evaporate. While we have around the same density of hair follicles, we have 10 times the number of sweat glands that chimps have. Most mammals have light skin that is covered by fur, and biologists believe that early human ancestors started out this way. What made us give up the protection from mutations, cold weather, waterproofing, and camouflaging? It could be since thermoregulation by sweating lets us hunt during the day in the hot grasslands without overheating, but there are other benfits to going hairless - advertising we are parasite-free to a mate, make it easier to read facial expressions.

79. Out of 510 million square km that is earth's surface area, 148 million square km is land. Starting from 800, 1400, 1700 and 1992 farmers took up 2.80, 4.6, 7.71 and 48.39 million square km (or 4.8 billion hectares since 1 square km is 100 hectares). Only 5% of the world’s lands are unaffected by humans. Atleast 75% of the earth's surface has been changed.

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Note that this is just land use for agriculture where Earth has a total of 14 billion ha of land (not all are arable), 3 billion ha is expected to be left.

80. The "Arabic" numerals were invented between 500 to 700 by Indian mathematicians. The decisive step was probably provided by Brahmagupta's formulation of zero as a numeral in 628. Arab mathematicians at the court of Baghdad were responsible for the diffusion of the Indian system of numeration in the Middle East and the West by 830. Middle-Eastern mathematicians extended the decimal numeral system to include fractions in 953.

81. Ancient Greece did not have any problem with homosexuality as evidenced in Iliad where Thetis had no objections towards her son Achille's relationship with Patroclus. Even Queen Olympias of Macedon was fine with her son Alexander the Great bringing his lover Hephaestion home for dinner.

82. When Spaniards first arrived in today's Veracruz, Mexico, natives bearing incense burners were assigned to accompany them wherever they went. The Spaniards thought it was a mark of divine honour, but we know from native sources that they found the smell unbearable. Native hygiene was far better.

83. Aluminium was discovered in the 1820s but seperating the metal from its ore was so costly that it was more expensive than gold. In the 1860s Emperor Napoleon III of France commissioned aluminium cutlery to be laid out for this most distinguished guests, less important visitors had to make do with the gold knifes and forks.

84. Phenoptosis  signifies the phenomenon of programmed death of an organism, i.e. that an organism's genes include features that under certain circumstances will cause the organism to rapidly degenerate and die off. This is exemplified by the Pacific Salmon (which dies after spawning), the mayfly (which lacks a functional mouth in its adult form), and Saccharomyces cerevisiae (under stress the baker’s yeast mitochondria produce reactive oxygen species ROS, leading to loss of membrane potential within the mitochondria and death of the cell). Other examples include the praying mantis (the male praying mantis ejaculates only after being decapitated by the female), the adatyllidium mite (the initial food source of the mite larvae is the body tissue of their mother) and squid (male squid die immediately after mating thus providing an abundant food source for predators that would prey on their eggs).

85. How did monogamy evolve? The extra nutritional requirement of having larger brains and the lengthier developmental period meant there is a need for biparental care. Monogamy also meant that men had time to ensure offspring survival rather than searching for other mates. It reduced within-group conflict. That is why serial monogamy is likely to have been dominating even among our ancestors. Human body size dimorphism is not that extreme like say gorillas, this further supports the idea that we have had monogamy for a while now. But other evidence indicates it is unlikely that monogamy has biological roots. Even in animals like birds that are famous for pair bonding for life have social monogamy, not genetic monogamy. We see non paternity rates of 19%. In fact no species is genetically monogamous.

86. In 19th-century BCE, more than a thousand years before the Noah's ark story was written we have Utnapishtim who was told by the God Enki to escape the deluge. There are many parallels to the Noah story and many scholars believe the Biblical story is based on this. Similar myths are seen in other cultures too with Deucalion using an ark to survive the flood caused by Zeus, and Manu in Hindu mythology.

87. The Earth's surface and its ionosphere (48 to 965 km)  are two conducting layers separated by air. The potential of 150 kV to 600 kV relative to the earth's surface is maintained by thunderstorms, with lightning strikes delivering negative charges. The ionosphere can reflect radio waves directed into the sky back toward the Earth, during the first half of the 20th century this shortwave radio communication was widely used.

88. The vampire bats practice lending in nature. They remember very well to whom they loaned the blood so at a later date if she returns home hungry, she will approach his debtor.

89. In ancient Egypt, each year surveyors had to redraw the boundaries of farmers field after the summer flooding of Nile. This activity gave its name to the study of shapes in general, Geometry - Ge (Greek for earth) + metres (measurer).

90. So we know that to make it harder for the invading bacteria to replicate, part of the immune response is to raise the temperature. The veins at the skin surface is constricted to trap the heat within the insides. This explains the chills since the temperature of the extermities decrease and we feel cold and start shivering.

91. During a typical lifespan, a person spends a total of about six years dreaming (which is about two hours each night). Most dreams only last 5 to 20 minutes.

92. We have exactly 10! seconds in 6 weeks. A million seconds is 1.65 weeks. A billion seconds is about 32 years.

93. The coronal heating problem in solar physics relates to the question of why the temperature of the Sun's corona (the outermost part of the Sun's atmosphere) is millions of kelvin higher than that of the its surface layer (photosphere is at 5,700 °C). Note the core is 15 million °C.

94. The genitalia of the female hyena closely resembles that of the male; the clitoris is shaped and positioned like a penis, a pseudo-penis, and is capable of erection. The male's penis enters and exits the female's reproductive tract through her pseudo-penis rather than directly through the vagina, which is blocked by the false scrotum and teste. The clitoris birth canal is only an inch in diameter, and the tissue often tears as a 2-pound cub squeezes through the narrow opening. Sadly, about 15% of first-time mothers die giving birth. This makes them the mammal with maybe the most painful way to give birth.

95. Red blood cells live for about four months, while different white blood cells live anywhere from days to years. Skin cells live about two or three weeks. Colon cells die off after about four days. Sperm cells have a life span of only five days, if not ejaculated then 74 days. Only about half of the heart’s muscle cells are replaced in the course of a normal lifetime. Our lens cells and brain cells stay with us till we die. Most of your body is younger than you are. But this is just one level of abstraction, look deeper than cells. Consider the atoms we are born with, almost all of them get cycled out yearly with atoms from the air we breathe or the food we eat. We are a pattern made up of atoms, we are not the material atoms themselves!

96. For some species, including humans, mortality – or the probability of dying within the next year of life – increases steadily towards the end of life. This is not, however, a regular pattern that applies to all species. The mortality of the gopher tortoise (Gopherus agassizii), which lives in the deserts of the southern United States and northern Mexico, decreases steadily with age. In other words: the older the tortoise gets, the less likely it is to die.

96. The Holocene extinction, otherwise referred to as the sixth mass extinction is ongoing right now with the current rate of extinction being estimated at 100 to 1,000 times higher than natural background rates, also 10 to 100 times higher than in any of the previous mass extinctions in the history of Earth.

97. In about one billion years, the solar luminosity will be 10% higher than at present. This will cause the atmosphere to become a "moist greenhouse", resulting in a runaway evaporation of the oceans. As a likely consequence, plate tectonics will come to an end, and with them the entire carbon cycle. After that in about 2 - 3 billion years, the planet's magnetic dynamo may cease, causing the magnetosphere to decay and leading to an accelerated loss of volatiles from the outer atmosphere. In about 3.75 billion years it will become far too hot for liquid water to exist, ending all terrestrial life. Four billion years from now, the increase in the Earth's surface temperature will cause a runaway greenhouse effect, heating the surface enough to melt it. The most probable fate of the planet is absorption by the Sun in about 7.5 billion years, after the star has entered the red giant phase and expanded beyond the planet's current orbit. You can use the cosmic calender to visualize such large time scales.

98. If Earth is not destroyed by the expanding red giant Sun in 7.6 billion years, then on a time scale of $10^19$ (10 quintillion) years the remaining planets in the Solar System will be ejected from the system by violent relaxation. If this does not occur to the Earth, the ultimate fate of the planet will be that it collides with the black dwarf Sun due to the decay of its orbit via gravitational radiation, in $10^20$ years.

99. The current hypothesis for the formation of the moon is a collision between a proto-Earth about 90% of the size of present Earth, and another body the diameter of Mars (half of the terrestrial diameter and a tenth of its mass). The latter has sometimes been referred to as Theia, the name of the mother of Selene, the Moon goddess in Greek mythology. The newly formed Moon orbited at about one-tenth the distance that it does today, and spiraled outward because of tidal friction transferring angular momentum from the rotations of both bodies to the Moon's orbital motion. Along the way, the Moon's rotation became tidally locked to Earth.

100. The Andromeda Galaxy is approaching the Milky Way at about 110 kilometres per second as indicated by blueshift. It is expected that it will directly collide with the Milky Way in around 4.5 billion years. The central supermassive black holes will collide and converge near the centre of the newly formed galaxy over a period that may take millions of years. The energy of this explosion will equal 100 million supernovae. While the Andromeda Galaxy contains about 1000 billion ($10^12$) stars and the Milky Way contains about 300 billion ($3 \times 10^11$). The chance of even two stars colliding is negligible because of the huge distances between the stars. If the Sun were a ping-pong ball, Proxima Centauri (our Sun's nearest stellar neighbor) would be a pea about 1,100 km away, and the Milky Way would be about 30 million km wide.

101. In a study, of 200,000 users found that female desirability to its male users peaks at age 21, and falls below the average for all women at 31. After age 26, men have a larger potential dating pool than women on the site; and by age 48, their pool is almost twice as large. Youthfulness is an important part of what makes us attractive.

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Christian Rudder used data from OkCupid to arrive at these conclusions.

102. Ancient Romans used both human and animal urine as a mouth rinse to help whiten their teeth.

103. In 1591, Eufame Maclayne was burned at the stake for asking for pain relief during the birth of her twins. Devout men and women believed that the pain in childbirth was a heavenly duty or that it was deserved. Pain relief became somewhat acceptable only when Queen Victoria asked Dr. John Snow for a whiff of chloroform to ease her delivery during the birth of Prince Leopold on April 7, 1853.

104. Thanks to geneticist Ha Ji-Hong, Korea’s loyal, shaggy-haired dog breed known as the Sapsaree, or Sapsali, has gone from a population of just eight in the 1980s to 1,200 dogs living with South Korean families. They were killed in large numbers by the Japanese military between 1910-1945 during the period of Japanese colonial rule. The dogs fur was used to make winter coats for its soldiers serving in the extreme cold of Manchuria.

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Sapsaree Dogs at Korean Folk Village attached to Yeongnam University in Gyeongsan, North Gyeongsang Province (Park Hyun-koo/The Korea Herald)

105. A single mammalian cell might contain as many as 10 million ribosomes; a single cell of the bacterium E. coli will have just tens of thousands. Each ribosome might crank out proteins by joining up about 200 amino acids (the constituent units of all proteins) per minute. Small proteins (<100 amino acids long) can therefore be made fairly quickly but two to three hours are needed for larger proteins such as the massive 30,000 amino acid muscle protein titin.

106. Upto 8% of our human genome consists of viral DNA inserted sideways into our lineage by retroviruses. Some of those viral genes, have even been co-opted to function in human physiology, such as creating an essential layer between the placenta and the fetus during pregnancy.

107. Arguably the variability of male traits (cognitive ability, personality traits, and interests) is greater than that of females, resulting in more males than females in the top and bottom of the IQ distribution. It was also seen that females usually performed better in verbal abilities while males performed better on visuospatial abilities. The most aggressive humans also tend to be male and 80% of violent crime is done by men.

There are many such traits -  where males are overrepresented on the bottom and top percentiles. One possible reason is that since males are the heterogametic sex, both are sex chromosomes are not the same this means unlike in the case of female, the effects are not averaged since there is only one X chromosome. Female selection pressure causes intense competition which should maybe? reduce variability, but the second reason could be that more risk makes sense in case of males for any family they will produce a high variance of men to get one in the top 25%, while a low variance of women is needed to ensure she is not in the bottom 25% since women marry up.

This idea is so feared that it caused a googler to be fired, Harvard President to resign and published papers to be replaced without due process.

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At both low and high IQ scores have almost 20% more representation. 

108. At least 4% of the population appear to be able to recognize absolute pitches (Perfect Pitch), whereas over 98% of the population can do the corresponding visual task of recognizing colors with no color standard present.

109. Humans and bananas share about 60% of our genes, 85% with a mouse, 96% with chimpanzees and 99.9% with other humans. Genes, which are the regions of the DNA that code for proteins, only make up 1.5% of your DNA. Atleast 8% regulates genes (as to whether a gene should be turned on or off). The other 90% is junk.

110. In orangutans, close human relatives, 'forced copulations' or rape may account for up to half of all observed matings.

111. Engineers at the Aerospace company Boeing used sacks of potatoes as stand-ins for passengers as they worked to eliminate weak spots in in-flight wireless signals. This is because potatoes (due to their water content and chemistry) absorb and reflect radio wave signals much the same way as the human body does.

112. On December 17, 1903 the first powered, heavier-than-air aircraft covered 61 m at a speed of 10.9 km/h at 3 m above the ground. The Wright brothers – Orville and Wilbur made this happen. But for years people did not believe it was possible. The Paris edition of the New York Herald summed up Europe’s opinion of the Wright brothers on Feb. 10, 1906: “The Wrights have flown or they have not flown. They possess a machine or they do not possess one. They are in fact either fliers or liars. It is difficult to fly. It's easy to say, 'We have flown.'” The world believed them after public demonstrations on August 8, 1908, 5 years later.

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First successful flight of the Wright Flyer, by the Wright brothers. Credits.

113. This shortage of empirical evidence has led many scholars to regard the entire topic of "Origin of Language" as unsuitable for serious study. In 1866, the Linguistic Society of Paris banned any existing or future debates on the subject, a prohibition which remained influential across much of the Western world until late in the twentieth century.

114. Jell-O is a sweetened gelatin product made by boiling the bones and hides of animals. The collagen in gelatin comes from boiling the bones and hides of animals processed for their meat (usually cows and pigs). But hooves consist of a different protein, keratin, which can't produce gelatin.

115. Ancient Hindus allowed polygamy with upper limit depending on your caste. A Brahmana can take three wives, a Kshatriya can take two wives and as regards the Vaisya, he should take one wife from only his own order. There is also evidence of polyandry happening in ancient India.

116. Ovulation typically occurs around day 14 of a 28-day menstrual cycle when an egg is released from your ovary. The egg can only be fertilized in the 12 to 24 hours after it’s released, but sperm can live in the reproductive tract under ideal conditions up to 5 days.

117. Today’s human population is descended from twice as many women as men. Throughout the entire history of the human race, around 80% of women reproduced but only for men it was only 40%. Premature male death in war, infidelity, or rape, slavery, inequality (rich men had more wives and their kids get better living conditions) are possible reasons. For some time around 4,000 to 8,000 years ago the ratio was 17:1.  

118. The symptoms of pseudocyesis (false pregnancy) are similar to the symptoms of true pregnancy and are often hard to distinguish from it. Such natural signs as amenorrhoea, morning sickness, tender breasts, and weight gain may all be present. Even though it is rare, in 2010, a woman in the United States who was suspected of being in labor was given a C-section only to discover there had been no fetus.

119. In September 1554, Mary the Queen of England stopped menstruating. Mary continued to exhibit signs of pregnancy until July 1555, when her abdomen receded. In August, soon after the disgrace of the false pregnancy, which Mary considered to be "God's punishment" for her having "tolerated heretics" in her realm. Edward VI the previous King and his father had sponsored the Reformation in stages, but Mary had always been Roman Catholic and considered Protestants to be heretics. By the end of 1554, the Heresy Acts were revived and the executions began from February 1555, in total, 283 were killed most by burning. Thus she earned the name Bloody Mary.

120. Consider Income inequality, in India naround 56% of national income goes to the top 10% of earners. The figure in France, UK and Germany is around 35%, in the U.K., it’s 40%. In the U.S., around 45%.

121. The lifetime risk of getting Melanoma Skin Cancer rate among Caucasians and African Americans is about 26.3 and 1 cases per 1000 people. However, the overall melanoma survival rate for African Americans is only 77 percent, versus 91 percent for Caucasians mainly because it's harder to detect.

122. The greatest officially recorded number of children born to one mother is 69, to the wife of Feodor Vassilyev (1707 - 1782), a peasant from Shuya, Russia. In 27 labours she gave birth to 16 pairs of twins, seven sets of triplets and four sets of quadruplets. A more recent record was Mariam Nabatanzi from Uganda who has 44 kids. Nadya Suleman (USA) gave birth to six boys and two girls at the Kaiser Permanente Medical Center, Bellflower, California, USA on 26 January 2009.

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Octomom Nadya Suleman hold the world record for "Most children delivered at a single birth to survive" - Eight.

123. Marsupials, including the most popular one, the kangaroo, are equipped with a total of three vaginas. The side-vadges are where sperm — from the males two-pronged penises — travel up, the middle-vadge is where the baby joey slides down to develop externally in the mother’s pouch after growing to the size of a jellybean in one of her two uteri.

124. While all 543 seats of the Lok Sabha go to the polls together, Only 1/3th of the 245 Rajya Sabha seats go to the polls every 2 years for a 6 year term. This creates a temporal inertia in politics and prevents a populist takeover of the legislative apparatus.

125. Venezuela's hyperinflation began in November 2016. Inflation of Venezuela's bolivar fuerte (VEF) in 2014 reached 69%, highest in the world. 1,698,488% in 2018 and then the govt stopped producing estimates. Prof. Hanke's HHIZ measure indicated that the inflation of the Zimbabwe dollar peaked at an annual rate of 89.7 sextillion ($10^21$) percent (89,700,000,000,000,000,000,000%) in mid-November 2008.

126. In human infants (starting from week 6), the hemoglobin molecule is made up of 2 α chains and 2 γ chains. The gamma chains are gradually replaced by β chains as the infant grows. It becomes less than 1% of total hemoglobin usually within the first year. Hemoglobin F has a different composition from the adult forms of hemoglobin, which allows it to bind (or attach to) oxygen more strongly.

127. Researchers have found that children had higher physical need scores than the other groups, the love need emerged from childhood to young adulthood, the self-esteem need was highest among the adolescent group, young adults had the highest self-actualization need, and old age had the highest level of security need.

128. Why are Russians and Americans usually larger than Asians? This could be a cold adaptation. Individuals with larger bodies are better suited for colder climates because larger bodies produce more heat due to having more cells, and have a smaller surface area to volume ratio compared to smaller individuals, which reduces heat loss. Shorter limbs help to conserve heat, while longer limbs help to dissipate heat.

129. The temperature that requires the least amount of energy investment is 21 °C (69.8 °F). Humid heat is dangerous as moisture in the air prevents the evaporation of sweat. The only mechanism the human body has to cool itself is by sweat evaporation. To handle cold we have shivering, which occurs in an unclothed person when the ambient air temperature is under 25 °C (77 °F) causes skeletal muscles to shake and temperature to rise. We also have non-shivering thermogenesis that occurs in brown adipose tissue (brown fat).

130. More than 3/8 of an inch (0.95 cm) in variation of the height of steps from one step to another is a tripping hazard. Sheldon claimed it was 0.2 cm so I was curious.

131. Foods that are rich in protein, such as meat, poultry, eggs, fish, spinach, tofu, cheese and soybeans, contain tryptophan amino acid. This amino acid is used by the body to produce serotonin, which is responsible for drowsiness. Overeating can also cause sleepiness. Post-meal, the body streams more blood to the digestive system to better digest foods in massive amounts. This causes a temporary blood and nutrients shortage in the brain.

132. In 900 AD, 3000 years after the the first writing - Sumerian logographs we invented spaces. The insertion of spaces between words made it possible, for the vast majority of readers to be able to read silently. Prior to this, most readers had to read out loud in order to be able to read at all. The few who could read text silently without these spaces between the words, like Julius Caesar and St. Ambrose, were viewed as so extraordinary that this ability is specifically recorded in historical records.

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Vergilius Augusteus, fragments of Virgil's Georgics, written in capitalis quadrata and in scriptio continua.

133. In 18th-century Europe, the then new practice of reading alone in bed was, for a time, considered dangerous and immoral. Some raised concern that reading in bed presented various dangers, such as fires caused by bedside candles. Some modern critics, however, speculate that these concerns were based on the fear that readers - especially women could escape familial and communal obligations and transgress moral boundaries through the private fantasy worlds in books.

134. Women find a partner’s emotional infidelity more distressing, while men find a partner’s sexual infidelity more distressing.

135. Birth order seems to affect sexuality. Each additional older brother increases the odds of a man being gay by 33%. One explanation for this is that male fetuses produce H-Y antigens which are "almost certainly involved in the sexual differentiation of vertebrates". These Y-linked proteins would not be recognized in the mother's immune system because she is female, causing her to develop antibodies which would travel through the placental barrier into the fetal compartment. From here, the anti-male bodies would then cross the blood/brain barrier (BBB) of the developing fetal brain, altering sex-dimorphic brain structures relative to sexual orientation, increasing the likelihood that the exposed son will be more attracted to men than women.

136. 2400 BCE – Khnumhotep and Niankhkhnum are believed to be the first recorded same-sex couple in history. 405 – Nonnus Dionysiaca is the last known piece of Western literature for nearly 1,000 years to celebrate homosexual passion. The Christian emperor Justinian I (527–565) made homosexuals a scapegoat for problems such as "famines, earthquakes, and pestilences. 1476 – Florentine court records of 1476 show that Leonardo da Vinci and three other young men were charged with sodomy twice, and acquitted. The Kingdom of France (Andorra, and Haiti) adopts a new penal code which no longer criminalizes sodomy. France thus becomes the first West European country to decriminalize homosexual acts between consenting adults.

137. Different parts of the eye have different response speed. The corner of your eye doesn't see color, but is fast and can see motion; the center sees color, and is slower.

138. Arguably, having more than 326 ppi won't matter for a human with 20/20 vision viewing from 10.5 inch away or more. But for 20/10 vision, 573 ppi is the limit at 12 inch and 458 ppi at 15 inch. The 6.55 inch 1+7T mobile has $1440 \times 3120$ pixels so a ppi of 524 is retina at 7 inch. 141 ppi for for the $1920 \times 1080$ 15.6 inch laptop which is retina at 61 cm.

139. When you look back in time, the perceived duration of an event involves the way the brain laid down the memory. The networks of neurons that code for a new memory are denser than they are for something that’s not novel. These denser networks make it seem as though that memory lasted longer. While in the present, time seems to fly when we are doing something novel since we are able to see the big picture of why it matters. When something is boring we focus on the short term results and we are more aware of time.

140. During the Paleolithic age (3.3 million to 11,650 years ago) there was only a 60% chance of reaching 15, but if you did life expectancy was an additional 39 years (total 54). After this old stone age upto 6,500 years ago, we have the new stone age or Neolithic period where this 39 dropped to 28 - 36 years. During the time of Greece (5th and 4th centuries BC) it increased to 37 - 41 years. From 1200 to 1550, if you lived till 21, you were likely to live to 60 to 70 years of age. Now in developed countries most people can expect to live upto 80.

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Now things have improved quite rapidly.

141. Approximately two-thirds of Americans shower daily. In Australia it’s over 80%. But in China, about half of people report bathing only twice a week. Daily showers do not improve your health and could cause skin problems or other health issues and they waste a lot of water.

142. One form of natural self-replication that isn't based on DNA or RNA occurs in clay crystals. Clay consists of a large number of small crystals, and clay is an environment that promotes crystal growth. Crystals consist of a regular lattice of atoms and are able to grow if e.g. placed in a water solution containing the crystal components; automatically arranging atoms at the crystal boundary into the crystalline form. Crystals may have irregularities where the regular atomic structure is broken, and when crystals grow, these irregularities may propagate, creating a form of self-replication of crystal irregularities. Because these irregularities may affect the probability of a crystal breaking apart to form new crystals, crystals with such irregularities could even be considered to undergo evolutionary development.

143. In the northern hemisphere, moss most often grows on the north side of trees. That's because the north side is the shadiest side in the northern hemisphere and the south side is the shadiest side south of the equator. As you move away from the tropics, the suns rays intersect the earth at an angle. Moss grows best in shady spots that are moist or humid.

144. In The Indian Evidence Act, 1872 we have a Section 114A: With regard to rape, where sexual intercourse by the accused is proved and where the woman states in her evidence before the court that she did not consent, the court shall presume that she did not consent.

145. Most women engage in hypergamy, marrying men richer, more sucessful, and taller than them. The top 78% of women are competing for the top 20% of men. Women marrying higher status, dominant men has evolutionary reasons.

146. Only about 2% of the U.S. population is of full Ashkenazi Jewish descent, but 27% of United States Nobel prize winners in the 20th century, 25% of the winners of the Fields Medal (the top prize in mathematics), 25% of ACM Turing Award winners, a quarter of Regeneron Science Talent Search winners, and 38% of the Academy Award-winning film directors have either full or partial Ashkenazi Jewish ancestry. Jews comprise up to one third of the student populace at Ivy League universities, and 30% of the U.S. Supreme Court's law clerks. In Great Britain, Jews are overrepresented among Nobel prize winners by a factor of 8.0. In Hungary in the 1930s, Ashkenazi Jews comprised 6% of the country's population, but 55.7% of physicians, 49.2% of attorneys, 30.4% of engineers, and 59.4% of bank officers.

147. Goodhart's law can be seen in practice if you consider The Great Hanoi Rat Massacre, 1902. Due to cases of the bubonic plague, the French colonial government took action. A bounty was set—one cent per rat—and all you had to do to claim it was submit a rat’s tail to the municipal offices. In the last week of April, 1902, 7,985 rats were killed—and that was just the beginning. On just June 21, the number of rates killed was was 20,112. Why were the numbers increasing like this? It turned out the hunters would rather amputate a live animal’s tail than take a healthy rat, capable of breeding and creating so many more rats. In the countryside on the outskirts of Hanoi, pop-up farming operations dedicated to breeding rats.

148. Facebook’s signature royal blue reflects Mark Zuckerberg's tastes. He is red-green color-blind, thus he chose blue because he sees it most vividly.

149. The Government of India raises about 80% of its total debt within the country using the RBI. The state govts have taken about 94% of their total debt from internal sources. The biggest sources of internal loans to the Government of India are commercial banks (40% of the total internal debt), 24% by insurance companies, and 15% by the Reserve Bank of India. Our public debt used to be 70% of GDP (Now its 90%). Of the external debt, bilateral is only 5%, even multilateral is only 10%. More than 80% is long term debt - commercial borrowings and NRI deposits.

150. Ferrero uses 25 percent of the global hazelnut supply. Each jar of Nutella contains about 50 hazelnuts.

151. In the first year of life, almost 100% of the skeleton is replaced. In adults, remodeling proceeds at about 10% per year. Bone remodeling is not just occasional "repair of bone damage" but the bones function as a bank or storehouse in which calcium can be continually withdrawn for use or deposited for storage. This occurs with the synchronized action of osteoclasts and osteoblasts, cells that resorb and deposit bone, respectively. Bones make up only around 15% of a person”s total body weight.

152. Amazon Fire Phone was such a flop that six weeks after launch the $200 phone was being sold for just 99 cents.

153. The French Code of Criminal Procedure prohibits hearing a suspect under oath; thus, a suspect may say whatever he feels fit for his defense, without fear of sanction for perjury. This prohibition is extended to the suspect's spouse and members of his close family. Even in Italy the defendant does not take an oath. They can lie without consequences. This right to silence has its origins in avoiding a trilemma of choosing to be silent and contempt the court, pejure or admit guilt.

154. Germanys defeat in WWI, 1918 led to the Kaiser’s abdication, a republic and a new constitution. The new Germany faced huge debts due to its punishment in the Treaty of Versailles. The Weimar government's main crisis occurred in 1923 after the Germans missed a reparations payment late in 1922. This set off a chain of events that included occupation, hyperinflation and rebellions. Prices ran out of control, for example a loaf of bread, which cost 250 marks in January 1923, had risen to 200,000 million marks in November 1923. By autumn 1923 it cost more to print a note than the note was worth. During the crisis, workers were often paid twice per day because prices rose so fast their wages were virtually worthless by lunchtime.

155. Why do birds avoid flying in the rain? Most birds are mostly waterproof. Their feathers, combined with oil from preen glands, keep them pretty watertight. Rainstorms tend to occur when atmospheric pressure is low. (When the pressure is low, the air is free to rise into the atmosphere where it cools and condenses) Air in a low-pressure system is less dense. But it’s dense air that gives birds the aerodynamic lift they need to take flight. (Lift is proportional to the density of the air and approximately proportional to the square of the flow speed.) Falling rain and high humidity also add lots of water molecules to the air. That water takes up space in the air, making it even less dense.

156. In the past, among Eastern European Jews, when a girl told her mother that she’d got her first period, the mother would slap her daughter’s face and, at the same time, exclaim “Mazel tov!” (congratulations).

157. Filler words such as um, er, or uh are used to indicate that the other person should continue listening instead of speaking, other reasons include pausing to give time for the speaker to gather their thoughts, speaking more indirectly in order to encourage politeness, approaching delicate topics gently, emphasizing ideas, providing clues to emotions or behaviors, and communicating uncertainty. Pauses are commonly used to indicate that someone’s turn has ended, which can create confusion when someone hasn’t finished a thought but has paused to form a thought.

158. Frigatebirds spent less than 3% of their time asleep, engaging in mid-air sleeping about 42 minutes per day on average and always at night. Having the largest wing-area-to-body-weight ratio of any bird, they soar continuously, they can fly higher than 4,000 meters in freezing conditions. Frigatebirds could remain on the wing for up to 12 days while foraging.

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National Audubon Society - Magnificent Frigatebird 

159. To divide the seats of our legislature proportionally, Article 82 of the Indian Constitution calls for the reallocation of seats after every census based on updated population figures. The Forty-Second Amendment enacted by Indira Gandhi in 1976 suspended the revision of seats until after the 2001 Census to promote family planning. In 2002 the Eighty-Fourth Amendment extended this freeze until the next decennial census after 2026 (i.e. 2031). However, the Eighty-Seventh Amendment (2003) did allow for redistricting within states based on 2001 population figures, although the total number of seats assigned to each state could not be altered. Right now, Members of Parliament from Tamil Nadu represent 1.8 million constituents per Lok Sabha seat on average versus 3 million constituents per Lok Sabha seat on average in Uttar Pradesh.

160. Rock salt is not salt sold in the form of rock shaped chunks but Halite which usually occurs within sedimentary rocks where it has formed from the evaporation of ancient seawater or salty lake water. It usually forms isometric crystals. The world's largest underground salt mine is the Sifto Salt Mine. It produces over 7 million tons of rock salt per year using the room and pillar mining method. It is located half a kilometre under Lake Huron in Ontario, Canada more than 800 km from the nearest ocean.

161. As per Roman Law, children under the age of 14, a child was considered to be doli incapax (incapable of criminal intent). A child older than 10, however, still had the possibility of being held responsible for a criminal act if it could be proven that they understood their offense. The age of marriage for girls could be as young as 12, and for men, around 25. In modern times, China has lowered the age of criminal responsibility for some serious crimes from 14 to 12. In 2004, Bangladesh raised the minimum age of criminal responsibility from 7 to 9 years.

162. Before the industrial revolution, in many parts of the world, including India, China and Eastern Europe, women tended to marry immediately after reaching puberty, in their mid-teens. In halakha ( Jewish religious laws), the term "minor" refers to a girl under twelve years and a day. A girl aged twelve and a half was already considered an adult in all respects. Most girls were married before the age of 15, often at the start of their puberty. In the Middle Ages, under English civil laws that were derived from Roman laws, marriages before the age of 16 existed. In Imperial China, child marriage (aged 14) was the norm. Manusmriti said 8 to 12 year old (For men 24 to 30). Mahabharata said 10. Menarche (first menstrual bleeding) occurs between the ages of 10 and 16 years and most girls complete puberty at ages 15–17. Paleolithic girls arrived at menarche between 7 and 13 years. Children in medieval England entered puberty between ten and 12 years of age. The average age of menarche is about 12.5 years in the United States, 12.7 in Canada, and 12.9 in the UK. A study of girls in Istanbul, Turkey, found the median age at menarche to be 12.7 years. Worldwide, an estimated 12 million girls are married every year before the age of 18 - nearly one girl every three seconds. Child marriage have h0rrible consequences on the girls health, education and safety.

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India has the largest number of child brides in the world – one-third of the global total. But there is progress - the prevalence of girls getting married before age 18 has declined from 47 per cent to 27 per cent between 2005-2006 and 2015-2016.

163. Evidence from 19th century Palestine suggests that husbands sometimes initiated sexual relations before their wife reached puberty, but that it was a rare occurrence, condemned socially and censured by sharia courts. Muhammad married Aisha, his third wife, when she was about six, and consummated the marriage when she was about nine.

164. The typical dietary contribution of calcium and magnesium in drinking water is over 80% of the total daily intake. Of this, approximately 30% of calcium and 35% of magnesium will be absorbed. The bioavailabilities of calcium and magnesium from milk and water are on the order of 50%. For calcium and magnesium, the typical contribution from water is 5–20%.

165. In his prime, champion cyclist Miguel Indurain had a resting heart rate of just 28 beats per minute. The usual range for resting heart rate is anywhere between 60 and 90 beats per minute. Above 90 is considered high.

166. The last common ancestor probably lived around 1415 BC, which will be approximately 120 generations ago, so let's say really remote people like the Karitiana tribe are, at most, something like 125th degree cousins of all of us. But practically you and that girl who lives near you are 40th to 120th degree cousins. Our last common ancestor with chimps was something like 5 to 6 million years ago. Our last common ancestor with cattle and dogs, about 92 million years ago, may be 30 million generations ago. With birds was around 310 million years ago.

This human Most Recent Common Ancestor is just the most recent human to be found in all living human's ancestral trees. Mitochondrial Eve and Y-chromosomal Adam are the most recent women and man (maybe Noah would be more appropriate) to have an unbroken matrilineal and patrilineal line with all living humans. Mitochondrial Eve is estimated to have lived about 200,000 years ago. Y-chromosomal Adam lived between 237,000 and 581,000 years ago (which is close to when homo sapiens split). Note how these are not individuals but titles, if more lineages die out the title will shift to a more recent Eve or Adam. It is also incorrect to assume that the MRCA passed all, or indeed any, genetic information to every living person.

Men had kids with many women while the converse was less popular which could explain why Adam is so much older. There is also the last universal cellular ancestor - 4.5 billion years ago and a point in the past where all humans alive were our ancestors or had no decendents alive now - around 5000 - 15,000 years ago.

Example of an eve - infographic
Eve's contemporaries had no surviving children. Or they only had sons, which wouldn’t have passed on their mitochondrial DNA. Same with Adam - male contemporaries of adam may also have descendants alive today, but not, by definition, through solely patrilineal descent; in other words, none of them have an unbroken male line of descendants (son's son's son's … son) connecting them to currently living people.

167. SSD read and write speeds are around 500 MBps while for HHDs it is 125 MBps. SSD's cost three times as much. HDDs have moving parts and can get damaged if you drop it when it is spinning. SSD is best for data you read often and write to rarely. (You can still write 300 GB every day for 3 years)

168. An intentional delay of 7 seconds is introduced when broadcasting live material. Such a delay may be to prevent mistakes or unacceptable content from being broadcast.

169. Infant mortality is significantly higher in boys than girls in most parts of the world. This has been explained by sex differences in genetic and biological makeup, with boys being biologically weaker and more susceptible to diseases and premature death. This is why more boys are born to ensure equal genders survive. More men die due to both natural causes such as heart attacks and strokes, which account for by far the majority of deaths, and also violent causes, such as homicide and warfare, resulting in higher life expectancy of females. Natural birth ratio is 1.07 to 1.03 males/females.

170. The Trivers–Willard effect explains how females in poor conditions (not dominant, lower in the hierarchy, low access to food, parasite load etc - glucose levels in blood serve as a proxy) tend to have more female children since a poor condition male would lose to better males and not get to pass on the genes.

171. Note how red is the least refracted color while colors of shorter wavelength like violet move slower (higher refractive index) and therefore the angle of refraction is larger (snell's law). How does dispersion work? the oscillations of the electrons in the material have a phase lag so interference causes reduced wavelength which means slower speed (continuity and energy conservation demands frequency is constant).

172. If you look at a red brick from inside water the red light of 700 nm should become 526 nm inside the water (refractive index of water is 1.33). But we don't see the color of the brick change because our eyes detect frequency of the EM wave which is constant throughout.

173. Overall, Earth's spin has slowed by about 6 hours in the past 2740 years. The most significant external causes are lunar and solar tides raised in the oceans and solid body of the Earth. Together with a further small solar contribution (the semi-diurnal atmospheric tide), these produce a steady increase in the length of the day of about 2.3 milliseconds per century (ms/cy) or 0.000000063 seconds per day.

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Earth's rotation imaged by DSCOVR EPIC on 29 May 2016, a few weeks before the solstice.

174. Hubble's law predicts that galaxies that are beyond Hubble distance (Around 14 billion light years) recede faster than the speed of light. However, special relativity does not apply beyond motion through space. Hubble's law describes velocity that results from the expansion of space, rather than through space.

175. People do not remember all parts of an event equally. Rather people judge an experience largely based on how they felt at its peak (i.e., its most intense point) and at its end, rather than based on the total sum or average of every moment of the experience. So people's judgments/memories of the unpleasantness of painful experiences depend very little on the duration of those experiences, gradual relief from pain helps a lot. This explains how mothers remember the most painful (objectively) experience of their lives, the end of the experience when she delivers the placenta has low pain levels and lasts 30 mins.

176. While nearly all humans can normally digest lactose for the first 5 to 7 years of their lives, the mammalian lactase gene's expression decreases after the weaning stage resulting in a lowered production of lactase enzymes. We had domesticated animals 9000 years ago but only around 7000 years ago did we do specialized dairying and that is when this gene is starting to be seen with most of the population around central Europe. Now even without the genes, we might still tolerate dairy products in which lactose is broken down by the fermentation process (e.g. cheese, yogurt) or healthy colonic gut bacteria may also aid in the breakdown of lactose. 66.6% of South Indians don't have this gene. While it is only 27.4% when it comes to North Indians.

177. A study at Yale–New Haven Hospital trains capuchin monkeys to use silver discs as money in order to study their economic behavior. The discs could be exchanged by the monkeys for various treats. During one chaotic incident, a researcher observed what appeared to be a monkey exchanging a disc for sex. Some pair-bonded female Adélie penguins copulate with males who are not their mates and then take pebbles for their own nest.

178. The lack of a functional ABCC11 gene affects apocrine sweat glands by reducing secretion of odorous molecules and its precursors. We also see smaller sized apocrine sweat glands and a decreased protein concentration in armpit sweat. The non-functional ABCC11 allele (dry-type earwax) is predominant among East Asians (80–95%), but very low in other ancestral groups (0–3% so wet-type earwax). Most of the world's population have the gene that codes for the wet-type earwax and normal body odor; however, East Asians are more likely to inherit the allele associated with the dry-type earwax and a reduction in body odor. The hypothesized reduction in body odor may be due to adaptation to colder climates by their ancient Northeast Asian ancestors.

179. Although serotonin is well known as a brain neurotransmitter, it is estimated that 90 percent of the body's serotonin is made in the digestive tract by enterochromaffin cells. Serotonin-norepinephrine reuptake inhibitors (SNRIs) are a powerful class of antidepressants. Naturally sunlight and excercise might increase it. Adequate levels are necessary for a stable mood.

180. Cats cannot taste sweetness, and several other carnivores including hyenas, dolphins, and sea lions, have lost the ability to sense up to four of their ancestral five taste modalities.

181. Chocolate manufacturers spend lots of energy grinding cocoa and sugar down to the right particle size for optimal acceptability - 20 and 30 microns particle size.

182. The Sanskrit term for 'human' is मानव (IAST: mānava). In Hindu mythology, Manu is the name of the traditional progenitor of humankind who survives a deluge and gives mankind laws.  This forms the etymology for the English word man.

183. There is a unfounded belief prevalent in Japan and South Korea, that a person's blood group system is predictive of a person's personality, temperament, and compatibility with others.

184. Paternity fraud is when a man is incorrectly identified to be the biological father of a child. It is often expected to be very rare but studies indicate it might be around 3.7%, which is 1 in every 27 people. This raises the question of what it means to be the father of a child, is it just DNA?

185.  Due to our success in getting more women into education and work, as well as greater access to contraception, women have more choices now. More women are choosing to have less or no children. It is expected that the number of people on the planet to peak at 9.7 billion around 2064, before falling down to 8.8 billion by the end of the century. Japan's population is projected to fall from a peak of 128 million in 2017 to less than 53 million by the end of the century. 23 countries - which also include Italy, Spain, Portugal, Thailand and South Korea are expected to see their population more than halve. Inverted age structure/pyramid will have drastic effects on our economy and retirement plans.

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2.1 fertility rate is what would ensure the population would remain the same. credits to BBC

186. Female babies are born with all the egg cells - oocytes they’re ever going to have (around 6 million becomes 2 million from fetus to birth). No new egg cells are made during your lifetime. Before puberty, more than 10,000 die each month. After starting her menstrual cycle, a woman loses about 1,000 (immature) eggs every month. So we can expect around 25,000 eggs at age 37 years; and 1,000 eggs at age 51 years. It is not just the number of eggs that determine fertility but also quality, older eggs have higher chances of causing say Down's syndrome. Age 30 to 32 is when fertility rapidly falls for women. While the impact on men is not as much, there is a 30% fall in fertility after 40 compared to less than 30 year old men. Sperm can cause birth defects too, 4 to 15% more for 35 to 50 year old males as compared to less than 20 year old males.

187. Unattractive criminals are punished higher (119.25% to 304.88% more fines) than attractive criminals for the same crimes.  Physically attractive individuals receive higher offers for starting salary, are more likely to be employed.

188. Speech is natural, it has been 100,000 years. The human brain is neurally adapted to learn to talk. Text is an invention only 6000 years ago. This is why reading and writing are acquired skills that need to be taught.

189. Located 36 km NW of the modern Pakistani city of Rawalpindi, lie the ruins of Taxila a great centre of learning. From 40 A.D to 5th century A.D. it flourished, considered one of the earliest universities in the world. Taxila was founded in a strategic location along the ancient "Royal Highway" that connected the Mauryan capital at Pataliputra in Bihar, with ancient Peshawar, Puṣkalāvatī, and onwards towards Central Asia via Kashmir, Bactria, and Kāpiśa. It is likely that St Thomas visited this university when King Gondopharnes was ruling.

190. Jesus mostly was born around 6 - 4 BC, and that his preaching began around AD 27 - 29 and lasted one to three years. It is likely he died around AD 30 and 36. It is also likely Thomas the Apostle ( one of the twelve primary disciples of Jesus Christ) came to Kerala in 52 AD to establish Christianity. By AD 72, Saint Thomas attained martyrdom in Chennai.

191. More than 40 million people around the world were victims of modern slavery in 2016. For comparison, current estimates are that about 12 million to 12.8 million Africans were shipped across the Atlantic over a span of 400 years. They were then sold in the Americas to work on coffee, tobacco, cocoa, sugar, and cotton plantations, gold and silver mines, rice fields, the construction industry, cutting timber for ships, as skilled labour, and as domestic servants. Modern slaves are far cheaper to buy, poverty forces them to stay stuck in these conditions.  In the olden form of slavery the cost of keeping slaves healthy was considered a better investment than getting another slave to replace them. In modern slavery people are easier to get at a lower price so replacing them when exploiters run into problems becomes easier. Debt bondage is India’s most common form of slavery despite being outlawed 40 years ago. This debt is passed down to children keeping them stuck working for no salary. In 2016 there were nearly 8 million people enslaved in India. 2.8 million people were slaves in North Korea, forced to work by the government. In Uzbekistan, for example, the government coerces students and state workers to harvest cotton, of which the country is a main exporter, every year; forcefully abandoning their other responsibilities in the process. An estimated 3.8 million adults were victims of forced sexual exploitation and 1 million children were victims of commercial sexual exploitation in 2016. ILO found that 152 million children  (aged between 5 and 17) – 64 million girls and 88 million boys – are subject to child labour.

192. Women do pee more often than men but not because they drink more. In fact, men generally have higher fluid intake but don't need to go as often. When men finally feel the urge, they tend to pee in higher volumes than women. This is because men have a larger bladder capacity. That means smaller bladders in the ladies. Women are also more likely to suffer from overactive bladder syndrome which makes them go even more. Women also tend to have a full bladder after sex.

193. The Breast Tax (Mulakkaram or mula-karam in Malayalam) was a tax imposed on the lower caste and untouchable Hindu women by the Kingdom of Tranvancore (in present-day Kerala state of India) if they wanted to cover their breasts in public, until 1924. The lower caste and untouchable women were expected to pay the government a tax on their breasts, as soon as they started developing breasts. The lower caste men had to pay a similar tax, called tala-karam, on their heads. Travancore tax collectors would visit every house to collect the Breast Tax from any lower caste women who passed the age of puberty. The very purpose of the breast tax was to maintain the caste hierarchy, it was a sign of respect towards the upper caste and the lower castes including Nadar and Ezhava women had to pay the "breast tax". The Nair women were not allowed to cover their bosoms while in front of the Namboodiri Brahmins or entering the temples, while the Brahmins bared their breasts only to the images of the deities. Uneasy with their social status, a large number of Nadars embraced Christianity, and started to wear long cloths. When many more Nadar women turned to Christianity, many Hindu Nadar women also started to wear the Nair breast cloth. From 1813 to 1859 several laws were enacted and removed by the Kingdom of Travancore regarding the upper cloth issue. In 1859 the violence reached its peak when two Nadar women were stripped of their upper clothes and hung on a tree in public for covering their breasts by Travancore officials. In the same year, under pressure from the Madras governor, the king issued the right for all Nadar women to cover their breasts.

194. One theory for male circumcision is that it was started to reduce the mans potential father a child with an older man's wife. This explained why this practice is more prevalent in polygynous societies, 48% of highly polygynous societies practice some form of male genital mutilation, and in societies in which wives live in separate households that increases to 63%. Only 14% of the monogamous societies in the database practice male genital mutilation. It is a misconception that the practice started for medical reasons, although both the Old and New Testaments make numerous references to circumcision, none relates to health. In keeping with this Rabbi Moses Maimonides (1135-1204), the famous physician and philosopher, does not mention any medical purpose to circumcision, although he was 800 years closer to the source than any 20th century speculators. The only benefit Maimonides could find for circumcision was that it weakened the penis and made men more temperate sexually. There are no compelling health arguments in favor of circumcision, and it is a risky operation. We have known this for many decades now. The attenuation and control of male (and by extension female) sensuality is likely the key reason.

195. Sleep serves many purposes, it restores the immune, nervous, skeletal, and muscular systems. It is crucial in the formation of long-term memory, learning and even removes toxins in your brain. The sleep cycle of alternate NREM and REM sleep takes an average of 90 minutes, occurring 4–6 times in a good night's sleep. REM sleep occurs more during body temperature minimum within the circadian cycle. During the REM phase, GABAB and ionotropic GABAA/glycine causes our body to be paralyzed, to prevent us from acting out what we do in our dreams. 7 to 9 hours of sleep is needed for adults.

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There are great benefits to synchronize with the Circadian rhythm. credit

196. Menstruation is the shedding of the uterine lining (endometrium). Contrary to popular belief it is rare among animals - only close human relatives, ten primate species, - simians (Old World monkeys -  baboons, macaques etc and apes), four bats species, the elephant shrew, and one known species of spiny mouse have been observed to menstruate. So usually female mammals resorb the endometrium if conception does not occur during that cycle.

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B. spiny mouse C. bats D. Elephant shrew

What could the reason be? It seems like menstration comes with many downsides - loss of nutrients, mood swings, tiredness etc. There are many theories and there is yet to be a consensus. One explanation is based on the maternal-fetal conflict, primate brains are hungry for resources and the placenta invades the mother, taking control of the bloodstream, pumping hormones into the mother etc. Spontanous decidualization (SD) evolved as an early protection from this for the rest of the body.

The second explanation is that it was a way to test the quality of the embryo, this is especially important since human embryos have a high risk of chromosomal abnormalities. About 30% of human pregnancies result in spontaneous abortion very early, which is the result of the mother's quality control mechanisms enabled by early decidualization.

Menstruation could thus be explained as a mechanistic consequence of SD. Other hypothesis like protection against pathogens in sperm, energy cost of maintaining lining, etc are not convincing. But it is important to keep in mind that for most of our history menstruation was quite infrequent (<50 over lifetime), due to frequent pregencies since puberty, low calorie diets, longer breast feeding. This is why increasingly menstrual suppression is being accepted as a lifestyle choice but there is yet to be a consensus on it's long term safety.

197. During pregnancy and just after childbirth the adult brain is most plastic. It is observered that pregnancy shrinks the brain’s gray matter, with it taking 2 years to recoup lost volume. This loss represents fine tuning of connections - "synaptic pruning,” a brain phenomenon that eliminates certain connections between brain cells to encourage the facilitation of new connections. The area where this happens is the same used for social cognition, the ability to figure out what someone else is thinking and feeling. These physical changes in the brain play a role in mothers experiencing a strong attachment to their child.

198. In India, Medical Termination of Pregnancy or Abortion is permitted only if there is a risk to the mother's life, could cause grave injury to her mental or physical health (including rape and failure of birth control measures), or in the case of foetal abnormalities.  Abortion can be done on the advice of one doctor for up to 20 weeks, and two doctors when it is between 20 and 24 weeks. Almost 56% of abortions in India are under the category of unsafe and abortion is, after hemorrhage and sepsis a leading cause of maternal death. But when does a baby gain human rights? when does abortion become murder?

Cognition is a continuum and it can't be immediately before exiting the vagina that the infant obtains the ability to feel pain. By end of week 5 to week 6 we see brain activity - unorganized neural firing and free nerve ending start to form. Some jurisdictions ban abortions after this point due to the heartbeat. By week 13 the fetus has begun to move. By week 15 the fetus has developed taste buds and will start to remember the taste of food that mom eats, they will also have developed receptors for pain throughout the body. By week 23 the fetus can survive outside the womb with medical support and can feel pain since neurons now extend from the spinal cord to the brain. By week 24 it can hear sounds. By 25 or 26 it responds to sounds.

Due to painkilling drugs crossing the placenta there are no norms in place for giving the fetus anesthesia before performing abortion. So it makes sense why after 24 weeks is the point where India put in the requirement for a Medical Board to recognize substantial foetal abnormalities. Any restrictions before that would just lead to crime, unsafe abortions etc. By week 30 fetuses seem to be capable of forming memory, and by 33 it should be able to feel heat, cold, pressure etc. Interestingly depending on the adult all episodic memories (memories of situations or events) before age 2 - 8 will be forgotten. If you look at reasons for performing abortion financial, career and relationship impacts are the major reason.

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59 crore (36%) women of reproductive age live in countries that allow abortion on request. 67 countries globally fall within this category.

199. Most women don't report orgasm solely from sexual intercourse and clitoral stimulation is important to most women. It is also interesting to note that the location of the clit is outside the vagina, the closer it is to the vagina the easier orgasm is. It is only 7 to 12 weeks in that the fetus starts to differentiate, so the clit might be the evolutionary side-effect of the male capacity for penile orgasm, a happy accident just like why males have nipples.

200. A rai stone are large and donut shaped that were carved out of limestone by the native inhabitants of the Yap islands in Micronesia. Rai stones were, and still are, used in rare important social transactions, such as marriage, inheritance, political deals, sign of an alliance, ransom of the battle dead, or, rarely, in exchange for food. Although the ownership of a particular stone might change, the stone itself is rarely moved due to its weight and risk of damage. Thus the physical location of a stone was often not significant: ownership was established by shared agreement, and could be transferred even without physical access to the stone. Each large stone had an oral history that included the names of previous owners. In one instance, a large rai being transported by canoe and outrigger was accidentally dropped and sank to the sea floor. Although it was never seen again, everyone agreed that the rai must still be there, so it continued to be transacted as any other stone.

Rai stones
A large (approximately 8 feet in height) example of Yapese stone (Rai) in the village of Gachpar

201. The most remarkable thing about the human genome is that it’s not very diverse. Humans have by far the least amount of genetic variation of any primate species. One single group of 55 chimpanzees in West Africa has twice the genetic variability of all humans. The population of humans dropped to as few as 3000 to 10,000 individuals. Something terrible happened to the human race. When? The mutation rate in our Y chromosomes suggests the bottleneck occurred 37,000 to 49,000 years ago. The mutation rate of single-nucleotide polymorphisms suggests 48,000 years ago. Dr. Reich’s study claims 27,000 to 53,000 years ago. The Toba catastrophe theory holds that around 75,000 years ago a super volcanic eruption caused a global volcanic winter of six to ten years and possibly a 1,000-year-long cooling episode.

202. Most human traits are polygenic, which means they’re determined by the combination of several genes from both parents. But some traits are X-linked - located on the X chromosome so can't be passed down from father to son, these are only given to daughters from the father. Because only males have the Y chromosome, the genes on this chromosome tend to be involved in male sex determination and development. There are also Y linked genes which are passed down from father to son.

The mitochondria, or the "powerhouse" of the cell, produces a cell's energy and plays an important role in exercise and aging. A mother's capacity for exercise can better predict a child's capacity since you get mitochondria's DNA only from your mom. There is evidence to suggest genes related to intelligence, autism, body weight, haemophilia, muscular dystrophy, red-green color-blindness are all maternally inherited. Height, coronary artery disease, sperm count, seems to be paternally inherited.

203. Across the world, U.S. has the world’s highest rate of children living in single-parent households. Almost a quarter of U.S. children under the age of 18 live with one parent and no other adults (23%), more than three times the share of children around the world who do so (7%). In 2010, 40.7% of births in the US were to unmarried women. The impact of unwed parenthood on mothers can be grave. Girls who become pregnant are likely to leave school, limiting their potential for educational advancement and economic security.

70% is an insane statistic
Since 1995, 70% of black mothers and since 2010 40% of all mothers in USA gave birth to kids outside of marriage.

204. Concealed ovulation is quite rare in the animal kingdom. Out of 32 species that hide their ovulations, 22 aren't monogamous but promiscuous or live in harems. Humans are considered to have concealed ovulation because there is no outward physiological sign, either to a woman herself or to others, that ovulation, or biological fertility, is occurring.

So why did humans evolve this? less paternity certainty would lower risk of infanticide, shared paternity might evolve, it allowed women to cuckold their husbands.

Concealed ovulation allowed the woman to mate secretly at times with a genetically superior man, and thus gain the benefit of his genes for her offspring, while still retaining the benefits of the pair bond with her usual sexual partner. Her usual sexual partner would have little reason to doubt her fidelity, because of the concealed ovulation, and would have high, albeit unfounded, paternity confidence in her offspring.

baboons sexual swelling
Ovulation is the release of an egg from your ovary, into your fallopian tube. Exaggerated swellings of the genitals of the baboon indicate the timing of ovulation, which can assure the paternity of the father.

205. 166 million years ago in the first mammals, the early “proto-Y” chromosome was originally the same size as the X chromosome and contained all the same genes. Deprived of the benefits of recombination, Y chromosomal genes degenerated over time and it is estimated at in around 4.6 m years or as early as 125,000 years it will disappear completely and men will go extinct. Just like male Japanese spiny rats and mole voles.

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The human X and Y chromosomes are widely different in length, the Y is largely non recombining and consist of tandem and palindromic repeats.

206. You can mathematically prove that according to evolution by natural selection, an organism that sees reality as it is will never be more fit than an organism of equal complexity that sees none of reality but is just tuned to fitness. Our perceptions are tuned to present to us a reality that is useful to us, to make us more likely to survive.

207. Ignaz Philipp Semmelweis was a Hungarian physician who was obsessed to figure out why infants were dying in his clinic. In 1847, he found out that washing hands reduced infant mortality by 90%. This was before germ theory was accepted and his hypothesis that cleaniness mattered a lot was rejected by the medical community, he was dismissed from the hospital for political reasons and harassed by the medical community in Vienna, and was eventually forced to move to Budapest. Nearly twenty years after his breakthrough, he was committed to the provincial lunatic asylum. He died there of septic shock only 14 days later, possibly as the result of being severely beaten by guards. It was only after 1864 that Louis Pasteur performed formal experiments popularising the germ theory.

208. Since ancient times in Western Europe, women could be medically diagnosed with a disorder called female hysteria, the symptoms of which included faintness, nervousness, insomnia, fluid retention, heaviness in abdomen, muscle spasm, shortness of breath, irritability, loss of appetite for food or sex, and "a tendency to cause trouble". Women considered suffering from the condition would sometimes undergo "pelvic massage" -  stimulation of the genitals by the doctor until the woman experienced "hysterical paroxysm" (i.e., orgasm). Paroxysm was regarded as a medical treatment, and not a sexual release. The disorder has ceased to be recognized as a medical condition since the 1920s.