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What was the central mystery of human evolution that you were trying to solve?

I was sitting next to the fire in my living room and I started asking the question, when did our ancestors last live without fire? Out of this came a paradox: it seemed to me that no human with our body form could have lived without it.

Why can’t a human exist on the same diet as a chimpanzee?

A chimpanzee’s diet is like eating crab apples and rose hips. Just go into the woods and find some fruits, and see if you can come back with a full stomach. The answer is you can’t. The big difficulty is that the nutrient density is not very high. This is problematic for humans because we have a very small gut, about 60 per cent of the volume it would be if we were one of the other great apes. We don’t have enough intestine to keep low-quality food in our gut long enough to digest it.

So cooking provided some kind of a watershed for humans to split from our chimp-like ancestors?

Yes. I believe the point at which our bodies show adaptation to cooking is 1.9 million years ago. The evidence is in the changes that took place when we evolved from ancestors that were like chimpanzees but were already standing upright. Cooking led to increased energy intake.

What was the result of having more energy?

Maximising energy from food allowed us to lose a third of the large intestine and significantly expand our brain size. It affected our brain because humans were social and there was a premium on being as intelligent as possible in order to outsmart your opponents in competition, ultimately for mates.

So there’s no physical proof of when cooking started?

From archaeological evidence, people estimate anything from 50,000 years ago to more than a million years.

You say that cooking led to the division of labour between men and women. How do you believe that happened?

Cooking imposes a delay between collecting food and eating it, which means others could steal from the cook. I worked out a simple model of social relationships that would let a cook keep the food. It relied on having a dominant set of individuals, the males, and a subordinate set, the females, who would cook but be protected by the males. We see this in many tribal societies – women cook for their husbands. There are two rules: a woman is obliged to feed her husband every night, and she is not allowed to feed another man unless her husband is present. If the whole society signs up to these rules, women are protected from thieves.

You have been accused of male chauvinism.

I’m just describing what happens, which is that women do the cooking in all societies except modern urban industrial ones. But that doesn’t make me a supporter of it. I’m not saying it is what should happen today.