the rise and fall of the third chimpanzee

Having a fourth kid could kill the mom and put the other three at risk. Human childbirth is particularly dangerous. Menopause is a solution to the risk taking behavior of having more kids. Turtles live long because it's worth repairing their bodies because they have good protection (shell) and so are unlikely to die a sudden violent death. Rate of aging across species is correlated with age of first reproduction. If you are likely to get in a crash that totals the car in the near future, then it's not worth investing in a lot of repair and maintenance. So given that it's going to fail, it's ideal/optimal if they all fail at the same time. The evolutionary reasoning is this: the body is only as strong as the weakest part. But it's not a conscious decision to scrap it. When do you scrap it? When everything breaks at once. Scheduled maintenance and unscheduled repair. Racial variation can be explained only partly by natural selection (correlation between skin pigmentation and latitude - which is nevertheless noisy) but it is also probably due largely to sexual selection which results from the mating preferences reviewed in the previous chapter.

We avoid people we grew up with between birth and 6 years, but then as adults we seek out partners similar to those people. Incest taboo is probably genetic rather than cultural. Couples tend to have a high degree of correlation (+.9) in religion, ethnicity, race, socioeconomic status, age, and political views (+.4) for personality and IQ (+.2) for physical traits (+.61) for middle finger length. Also unlike most mammals, humans have sex all the time and it's purpose is largely social rather than merely for reproduction. Unlike most mammals, human ovulation is concealed and sex is done in private. Roughly 10% of babies are adulterously conceived.

Humans have exceptionally large penises and breasts for our body sizes. Across primate species, degree of polygyny is correlated with sexual dimorphism in body size and other physical features, and also testis size of males. Progress no longer depended on genetic evolution but cultural evolution. The Great Leap Forward occurred 40,000 years ago with the emergence of spoken language. Cro-Magnons and Neanderthals co-existed 100,000 years ago (from 130,000 years ago until 40,000 years ago).

Hunter-gatherers were probably poor hunters. We descended from Cro-Magnons, not Neanderthals. Chimps are more closely related to humans than to gorillas. We share 98.4% of DNA with common chimps. Our ancestors diverged from other apes around 7 million years ago. Not at all a comprehensive outline, but may be of interest to some people. Here are my favorite bullet points from The Third Chimpanzee. I find that his books have so much information that it is helpful for me to outline them as I go. I found this to be just as engaging as Guns, Germs, and Steel, and also an easier read.

The rise and fall of the third chimpanzee