Notes on de Waal's "Tree of Origin"

Some random notes on Frans de Waal's "Tree of Origin: What Primate Behavior Can Tell Us about Human Social Evolution," a book I had mentioned briefly in another post.

• Page 47: says modern hunter-gatherer tribes rely more on plant foods, usually gathered by women, than by meat hunted by men. Vegetarians love to say this too. Maybe right today, but there's a bias in relying on modern tribes as a reference. They've been pushed out from the coasts and the most fertile hunting grounds by "advanced" groups, and have to make do with the wastelands. I'll bet most hunter-gatherers had more meat than modern groups did.
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• Page 64: contrasting human breeding patterns to chimps, it says "the nuclear family relies on paternity certainty." I think modern paternity testing plus the availability of abortion may change genes affecting human personality - the male genetic strategy of "cuckolding" without having to invest resources in the offspring works less well, the male strategy of monogamous investment in children no longer carries the risk of being cuckolded, and "straying" females are more likely to abort pregnancies that might be the result of a liason.
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• Page 143: in the last 1.9 million years, hominid sexual dimorphism has stayed roughly the same, despite massive changes in brain capacity. Gender dimorphism generally gives some clue about sexual relations. Our moderate level of sexual dimorphism suggests moderate polygyny, again very different from our chimp and gorilla relatives. Interesting that this has been stable through our ancestral species too.
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• Page 168: larger apes seem smarter than smaller monkeys, despite having similar neocortex/body size ratios. The book says that one explanation besides a better-wired brain is that "rather than relative neocortical enlargement, absolute size is what matters. When the total brain volume reaches a certain point, the ability to perceive and organize the structure of instrumental behavior emerges." My comment is, what about cetaceans? If only a small fraction of a sperm whale's 20-pound brain exceeds what's needed for body control, that's likely to be a scary amount of brain matter available for cognition. The author goes on to suggest that testing whales would be interesting, although I'd guess that experimental testing of adult sperm whales would be a challenge.
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• Pages 180-183: the most interesting part of the book. Neocortex/body size ratios for primates correlate positively along a line for each primate species typical group size. Applying the same neocortex ratio to humans gives a group size of 150, which the author argues fits well with the group size found for hunter-gather clans. Humans have other group sizes, he argues, but they're either much larger or much smaller than the 150 figure. And he claims modern groups fit similar size structures. The apogee of the neocortex ratio can be found with Neandertals, who could theoretically manage slightly larger groups than we can.

Like I said before, it's a good book and well worth reading.