This book offers a compelling case for the idea that cooking is the main reason why we evolved from australopithecines to Homo erectus and then to Homo sapiens. It challenges at several points the mainstream notion that meat-eating was a keystone of (at least some parts of) this evolution, for having comparatively limited explanatory power. Besides the anatomical changes it uses cooking to explain some things I wouldn’t have expected, such as marriage and the sexual division of labor.

I thought the point was generally well-argued and at the same time the book provided enough interesting bits to keep a wide audience interested. There are plenty of anecdotes (favorite example: the author adds tough leaves to a raw goat meat meal to test that they make chewing easier), and many references to actual studies in the endnotes for the true nerds.

It has a problem that might be unavoidable in this kind of pop-sci book: there’s always a lot of uncertainty in modern science (especially in something with as little archeological evidence as fire), but, because the author wants to make their case as persuasive as possible, diverging points tend to be omitted or minimized. As a result, it’s sometimes hard to know what’s well established and what’s controversial. For example, a core point in the book (why is the human brain so unusually large?) relies on the Expensive tissue hypothesis. The author does note that it’s a hypothesis, but there’s no exploration of why it’s still one, or how accepted it is in the field.

I wrote a summary of each chapter, plus notes on bits I find interesting and references.

The Cooking Hypothesis

Man evolved from australopithecines into habilines and then to Homo erectus and then to Homo sapiens. A popular theory to explain how that took place is that we evolved to hunt meat. Hunting would’ve required a degree of tool development and cooperation that australopithecines wouldn’t have been capable of.

This theory fails to explain how this evolution would also have enabled gathering, which is crucial to make the hunting lifestyle possible. (Sometimes you come back empty-handed from a hunt.) It also fails to explain how the jump to Homo erectus, who had an upright posture and weaker jaws and teeth than their predecessors, could have evolved from habilines. Could cooking explain that evolution? The answer this book provides is yes.

Quest for Raw-Foodists

Like other animals, humans can live off a completely raw food-based diet. However, it seems that we have a hard time getting enough energy from raw food alone. There have been experiments where people have gone on a raw food-only diet, such as the Evo Diet experiment, and they always end with people having lost weight. A more striking example is the Giessen raw food study, which had the further result that about half of the women in completely raw food diets had stopped menstruating. Such a strong effect on reproductive function indicates that we have evolved to eat cooked food.

There aren’t concrete reports of any cultures that survive exclusively on raw food. Some eat more raw food than others, but all societies seem to rely on cooking. There are also no examples of people surviving long-term on raw food (except perhaps Helena Valero, who claimed to have lived off bananas for 7 months.)

The Cook’s Body

Why did we evolve to eat cooked food and lost the ability to process raw food efficiently? It could be an evolutionary tradeoff. First, once we started cooking we immediately got the benefits from the extra energy cooked food provides. Then, we evolved a smaller digestive system, which allowed to process cooked food more efficiently. At that point we lost the ability to live off raw food.

There’s ample evidence supporting the first step: many examples of animals (including insects) that grow better on cooked food. For the second step, we can observe that we have much smaller mouths than our relatives (for example, chimpanzees can open their mouths twice as wide as humans), tiny lips and much weaker jaws. Our stomachs are also very small, which makes sense given the high caloric density of cooked food, and our large intestines are about half the size of what a primate with our body weight normally would be, which explains why we can’t process plant fiber as efficiently as great apes.

Could these changes be explained by us having evolved to eat meat instead? Our mouths and jaws aren’t very good at eating raw meat. Also, we don’t keep food in our stomachs for a very long time, which is important for digesting raw meat. (For example, cats keep food in their stomach from five to six hours; for humans, it’s one or two.) More importantly, plants would have been a key component in the diet of tropical hunter-gatherers, so meat-eating alone cannot explain why they would have evolved such small digestive systems.

Another interesting bit: we seem to have some resistance to Maillard compounds, such as acrylamide, which has been shown to be carcinogenic in animal models. Maillard compounds are a by-product of cooking (in particular overcooking), so this could be evidence that we evolved for cooked food. By contrast, we have very little resistance to bacteria that live on raw meat.