p. 101: “For a mother with a small infant, the gymnastic challenges of making a nest would have been particularly difficult given her need to cradle while she swayed in the tree.”
What in the world is that sentence talking about? Well, most apes (except for enormous male gorillas) spend the night up in trees, sleeping in “nests” made by bending branches into a secure platform. It’s safer up there. But what did early humans do, once our ancestors had long legs and flat non-gripping feet like ours? How on earth could they have kept their balance every single night to make a nest, and if they slept on the ground, how did they keep from being eaten?
Wrangham argues that people – or not-yet-exactly-people – learned to control fire a very long time ago, going on two million years in the past. (Not all anthropologists would agree.) His argument leans on several observations. First, he collects data from a number of sources to insist that modern humans, living with primitive technology, couldn’t possibly get enough calories from a completely raw diet. (For example, he says modern raw-food eaters (who shop in supermarkets and use blenders and other advanced equipment to process their seeds and raw vegetables and fruits) are all very lean, and there’s evidence that many of the women would not be fertile. Stone-age people would have had to work much harder to provide the same diet; they probably wouldn’t have survived.) He also argues that there’s no evidence any primitive group lived without cooked food, and presents data to show that cooking makes food not just easier to chew but less work to digest – all of which means that cooked food provides more calories. That’s not what most of us want today, but for many thousands of years people lived a lot closer to the edge of survival and needed all the food energy they could get!
Then he compares human anatomy to ape anatomy. In addition to huge jaw muscles that go all the way up to the tops of their skulls, apes have enormous digestive systems – reflected in their flared rib cages. From the time of homo erectus (a human ancestor living from about 1.8 million years ago to about 800,000 years ago) onward, surviving skeletons have narrowed rib cages like ours, as well as legs and feet that wouldn’t work well in trees. Wrangham believes that this means very early humans were cooking their food and spending the night around campfires that would let them see predators and drive them off – maybe with burning sticks.
And after all that, he goes on to speculate about what cooking meant to human family life and social structures. Catching Fire is solidly packed with ideas. It’s a short book, only about two hundred pages plus another fifty pages of notes, and I can’t do justice here to all of Wrangham’s argument. Read it for yourself!