Now that we have seen a few examples of how sexual selection has shaped our bodies, we can step back and consider how the human body's evolution relates to the human mind's evolution. In the mid-20th century, many evolutionary theorists suggested that human bodies represent a degeneration from the wild, robust strength of other apes. They speculated that our supposed bodily weakness somehow forced our brains to become strong, so we could hold our own in the competitive ecology of prehistoric Africa. Reflecting this view, a persistent theme in Robert Heinlein's "Waldo" science fiction stories of the 1950s was that, as humans were allegedly ten times weaker and ten times smarter than chimpanzees, our space-faring, zero-gravity descendants will be ten times weaker and ten times smarter than us. Anthropologist Ashley Montagu influenced a whole generation of anthropologists with his view of neoteny: that the human body is weaker and more childlike than ape bodies, giving it a generality and flexibility uniquely suited for culture.
However, this compensatory view that our brains made up for our lack of brawn does not fit the fossil evidence. Since the rise of Homo erectus 1.7 million years ago, our ancestors were among the largest and strongest primates ever to have evolved. Homo erectus males seem to have averaged almost six feet tall, with robust skeletons suggestive of powerful muscles. When modern Homo sapiens lived as a hunter-gatherer in reasonably food-rich environments, they also grew tall and massive. While brain size was tripling in our ancestors, body size was increasing as well. We are two feet taller and twice as heavy as our earliest bipedal ancestors of 4.2 million years ago. They would be more immediately impressed by our astounding size and strength than by the little puffs of air we call language.
For the last 2 million years, our ancestors have been larger than any insect or amphibian, and larger and stronger than about 90 percent of birds, reptiles, and mammals (to a first approximation, most mammals are rodents and rabbits). Among more than 300 species of modern primates, only male gorillas (averaging around 350 pounds) are significantly larger than humans (around 150 pounds); female gorillas and male orangutans are slightly heavier than male humans, while male chimpanzees weigh up to 130 pounds, and bonobos up to 90 pounds, for both sexes. Our ancestors were the most powerful omnivores in Africa. There were some larger hoofed herbivores, a handful of larger carnivores, and the odd elephant, mastodon, hippopotamus, or rhinoceros. But once our ancestors evolved the ability to throw stones, to wave torches around, to attack in groups, and to run for long distances under the midday sun, they were probably the most terrifying animals in Africa. It is a wonder they bothered to evolve more intelligence at all.
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