Once cooking happens, it completely changes the way the animal exploits its environment, because instead of moving from food patch to food patch, and eating as it goes, or eating in the food patches it finds, now for the first time it has to accumulate food, put it somewhere, and sit with it until it's cooked. It might take 20 minutes, it might take half an hour, it might take several hours. The effect is that all of a sudden there's a stealable food patch. Once you have a stealable food patch, that means that — life being what it is — somebody's going to come along and try to steal it. What this means is that you have to think about a producer/scrounger dynamic in which you've got individuals producing and individuals scrounging — and, horribly, females were the producers and males were the scroungers. Once you've got males bigger than females — fifty percent bigger by the time we're talking about, around two million years ago — then the effects on the social system would be large.

What we've got to think about is the idea that once you have females ready to make a meal by collecting food and cooking it, then they're vulnerable to having their food taken away by the scroungers — the big males — who find it easier not to go and collect food themselves or cook it, but just take it once it's ready. Therefore the females need protective bonds in order to protect themselves from thieving males, and this is the origin of human male-female relationships. The evolution of cooking is a huge topic that is virtually completely neglected. And whatever view you take about cooking, you have to say it's a problem that needs to be addressed.

The second problem is this: There is in a number of ways in the evolution of humans evidence of our behaving and looking as if we had the characteristics of a juvenile animal. For a hundred years or more people have talked about the idea that humans might be a pedomorphic species, a species that has juvenile characteristics in general, but this is too global a way to think about it. Still, it remains the case that much in our behavior, when compared with the behavior of our closest relatives, looks more playful and less aggressive when you're thinking about interactions at a social level within a group. We are also more sexual and more ready to learn, and these sorts of characteristics are characteristics generally associated with juvenility.

In a fascinating parallel, the bonobos — the second in the great pair of our two closest relatives — show all sorts of traits that are pedomorphic. We can see this throughout the head, where the morphology of the skull itself looks like the skull of an early adolescent or late-juvenile chimpanzee and much of its behavior looks juvenile-like. They are more playful, they're less sex-differentiated in all sorts of aspects of their behavior, they're more sexual, and so on. And we've yet to really come to grips with where this pedomorphic change has come from and what it means.

We've already got some wonderful examples of similar things occuring in other animals in the context of domestication. When we look at the differences between wolves and dogs, for example, we see amazing parallels to the differences between chimpanzees and bonobos. In each case for a given size of animal, you have the skull being reduced in size, and the components of the skull being reduced in size, including the jaws and teeth, and the skull looking more like the skull of a juvenile in the other form. The dog's skull looks like that of a juvenile wolf, and the bonobo's skull looks like that of a juvenile chimpanzee. And the behavior of each of them looks like it has strong components of the juvenile of the other species.

This leads to the thought that species can self-domesticate. There is good reason to think that over the course of evolution the bonobos evolved from a chimpanzee-like ancestor as a consequence of being in an environment where aggression was less beneficial to the aggressors, where there was a natural selection against aggression, and where selection favored individuals that were less aggressive. Over time, selection built on those slight variations in the timing of the arrival of the aggressive characteristics in the adult males. So it was constantly pushing back, favoring individuals that retained more juvenile-like behavior — and even juvenile-like heads — because that's what controls the behavior. Later, what you had was a species that had effectively been tamed, had been self-domesticated.

There is experimental evidence of this process. We have the Russian geneticist Belyaev, for example, who actually took wild foxes, selected for purely tame traits over 20 or 30 generations, and at the end of that time observed not only that the descendant foxes are as tame as dogs are nowadays — spontaneously — but also that they have a series of characteristics that have come along for the ride, incidental consequences that were not selected for but are just there. You have dramatic morphological ones, like the star mutation — the white spot on the forehead that you see in horses and cows and goats — that are just somehow associated genetically with tameness, and probably result from some kind of change in developmental events. There are also other morphological changes, like curly hair, short tails, and lopped ears, which happened in a number of domesticated animals, apparently because they've been selected for tameness. In addition, you get these smaller brains.