A Natural History Of Ourselves (2)
Here’s the first post in the series. There are lots of interesting ‘bites of an apple from the tree of knowledge’ in the book, so I’ll just go ahead and post some of them here. From the first three chapters (~100 pages) :
i. “Two centuries after Captain James Smith (five four, perhaps) dropped anchor at Jamestown in 1607, the average U.S. male had gained two or three inches, depending on whose data you use.”
ii. This explanation neglects the problematic hair on my head, though. The best theory here relates to my massive brain […]. Theory goes: The head of my ancestral hominids, as they reared upright, was exposed to the tropical sun. As the brain of hominids evolved larger, this head fur grew in importance. A brain is a steaming wad of fat, a three-pound radiator. It’s vulnerable to high temperatures and will fry out at 107.6°F (42°C). So it’s insulated against the sun with a mop of fur, and it’s cooled with a surfeit of sweat glands. That’s the predominant theory, anyway: We shucked the body fur in order to cool our bodies better, but kept the head hair to prevent the brain from baking. My tresses shield my brain from the sun, the way a sheep’s fleece keeps it cool in the desert. And the rest of my skin is open to the wind so I can sweat cool as I sprint after hamburgers on the plains of South Portland.”
iii. “Until you give the human animal tools, it is pitifully armed, and not dangerous. This isn’t normal, among primates. Cousin Chimp’s weapon of choice is his large teeth. […] Gorillas and orangutangs, as well as the other primates, also rely primarily on their teeth to wound and kill their rivals [and prey]. […] I don’t believe my jaws are up to the challenge of biting off human fingers, let alone severing an ankle. Humans don’t fight much with our teeth. Generally, we prefer metal tools, and generally the longer the reach of the tool, the better. When a human does tangle without tools, the weapon of choice is the hands. […] the male fist is the most common cause of broken jaws. […] In my culture, only one killing in fourteen is accomplished without tools.”
iv. “A running chimp is as graceful as a tumbling brick.”
v. “This animal [humans] perceives the world foremost with its eyes. As in many predators, the eyes are forward oriented. This produces three-dimensional vision but narrows the total field. Inside the eye, the human (like many of its fellow primates) has three cones rather than two, producing color vision much richer than that perceived by most mammals. […] Taste and smell, the chemical senses, are rather weak. The tongue can, however, identify poisons with passable accuracy and is sensitive to high-calorie sugars and fats. […] Females demonstrate a slight edge over males in the speed at which their brains process sensory information – especially during the fertile phases of their menstrual cycles.”
vi. “The eyes of all animals had a humble beginning. Some single-celled somebody probably got the vision thing rolling when a DNA flub granted it a light-sensitive chemical. This dab of chemistry may have allowed an ancestral Mr. Microbe to eat better, or to better avoid being eaten, and thus he [it] thrived. And everyone who evolved from him was grateful for his revolutionary photopigment.
Today, each species packages its photopigment a little differently (or a lot differently), but the general rule is the same: You collect a subset of the light spectrum and use the data to plot your next move. You don’t even require a brain to do this – the marine brittle star is paved with crystals that detect a predator’s shadow and signal its five arms to scramble for shelter. […] As for processing speed, my eyes are rather indolent. When I sit watching a movie, the series of still images blends together to form motion. But to a fly, a movie plays like a plodding slide show. […] A fly can process two hundred different images in a second. I can handle twenty before they start to blur.”
vii. “Just as my predator’s eyes leave me blind behind, my ears leave me with a “deaf spot.” Humans have trouble locating noises that are directly fore, aft, or above our heads. […] As for ear location, I’m pretty normal. Most mammals separate their ears to maximize their triangulating potential. Still, they keep them handy to the brain that processes sound data. […] My own ears are so far apart that a sound wave registers first in one, then a split second later in the other. The sound level drops, too, in the time it takes to reach the second ear. Between the time lag and the pinnae’s input, my brain can calculate where to point my eyes.”
viii. “the male and female human perceive pain differently – even after accounting for the COMT gene. The sex hormones that soak our respective brains seem to dictate how each sex will experience life’s cuts and contusions. Generally, females have a lower threshold: It takes less burning, freezing, poking, or pinching to make them yelp. They also have a lower tolerance for pain: They’re quicker to capitulate and pull their hands from a bucket of ice water or a heat beam. (These are common tools of torture for pain researchers.)
Other differences hint at the separate ways that male and female bodies react to pain. During painful times, a male’s heart beats faster but not the female’s. A male’s cortisol and endorphins (stress chemical and painkiller) rise, but for some reason, a female brain neither stresses out nor self-medicates for pain. […] Why? Most theories cluster around a female’s role in reproduction: She must avoid harm “for two,” so to speak.
Curiously, the human female’s pain sensitivity goes dull when her estrogen level rises toward the fertile days of her monthly cycle.”
ix. “Female siblings who live together will, like mice, rapidly synchronize their menstrual cycles in about half of cases studied. About one-third of close friends who spend lots of time together will synchronize, too.”