Cooking and the evolution of human digestive anatomy

Cooking makes food easier to eat. Why would our bodies need to change to handle something easier? That is the reasonable expectation the opening introduces. But there is another possibility: once cooked food is available, traits that help us use it efficiently could become advantageous, even if we did not need those traits to take the first bite.

The authors point to a problem for the original expectation. Humans today generally have difficulty surviving on an entirely raw diet in the wild. Much raw plant food is difficult to digest, and much raw meat is tough to chew. This is not a claim that we cannot eat a raw carrot or that no one can live on raw food. The authors allow unusual circumstances, such as a sedentary life in a well-supported urban setting. Their question concerns the demands of surviving on raw food under ordinary conditions in the wild.

That gives us a possible consequence of cooking: we may have become dependent on food that is easier to chew and digest. Cooking began as something that made eating easier, but adaptations to cooked diets could leave later humans less able to manage without it. Keep that proposed change separate from the idea that humans first needed special adaptations just to eat cooked food.

Was there enough time for cooking to affect evolution? Some people assume the practice is too recent. The authors answer with evidence of fire use and apparent earth ovens at sites more than 250,000 years old. Those finds matter because they give cooking a long possible history. They do not identify the exact moment it began or prove that every population was already eating mostly cooked food.

The first paragraph ends with the proposed explanation: cooked food allowed humans to use calorie-dense diets more efficiently, and selection for that efficiency reduced their ability to survive on raw diets in the wild. The authors are suggesting an evolutionary tradeoff, not simply announcing that cooking made people weak or unhealthy.

The second paragraph asks what that change might look like in our bodies. Teeth and jaws provide one possible answer. Tough raw meat requires more chewing; softer cooked food could reduce the advantage of large teeth and powerful jaws. Human teeth and jaws began decreasing in size around 100,000 years ago. Regional differences in when that happened also broadly fit differences in when improved cooking methods were adopted. That fit supports the proposed connection, though a correlation does not by itself settle the cause.

Then the authors consider an earlier possibility. A reduction in teeth and jaws accompanied the appearance of Homo ergaster about 1.9 million years ago. If cooking contributed to that change, the reduction around 100,000 years ago might reflect a later improvement, such as boiling, rather than the first adoption of cooking. We therefore have a possible sequence of developments, not a single date at which cooking and every anatomical change began.

What about the rest of the digestive system? Soft tissues do not leave the fossil record that teeth and jaws do, so their history is harder to reconstruct. We cannot simply inspect an ancient intestine in the same way we inspect fossilized teeth. The authors instead discuss differences between modern humans and other great apes: smaller gut volume, a longer small intestine, and a smaller colon.

Those features have traditionally been explained as adaptations to a diet high in raw meat. But what do the features actually indicate? A diet of relatively high caloric density. Cooked food could provide that too. If both diets can explain the same anatomy, observing that anatomy does not uniquely establish the raw-meat explanation.

The authors therefore want the cooking explanation tested against the raw-meat model. Their central claim is that cooking appears to have shaped human digestive anatomy, leaving us adapted to cooked rather than raw diets. The ending preserves the distinction between a promising explanation and one that the evidence has definitively proved.