The evolution of crying

Carl Zimmer has a very nice piece on the evolution of crying and colic on his weblog, The Loom.

The most interesting part is a review of recent work by Hillary Fouts in Current Anthropology. The gist of this work is that children at the time of weaning have different strategies in foraging groups compared to farming groups. From the abstract:

Parent-offspring conflict theory suggests that the reproductive interests of parents and children may conflict when parents want to have another child and an existing child wants continued parental attention and resources. This conflict leads toddlers to throw temper tantrums and use other psychological weapons to maintain parental investment. Few studies employing this theory have considered both the cultural and the biological contexts of weaning. Using systematic qualitative and quantitative data collected among the Bofi farmers and foragers of Central Africa, we examined the influence of cultural schemas and practices, nursing patterns, child's age, maternal pregnancy, and maternal work patterns on children's responses to the cessation of nursing. As predicted by the theory, Bofi farmer children exhibited high levels of fussing and crying when abruptly weaned while Bofi forager children showed no marked signs of distress.

But as Zimmer describes the situation:

But the researchers kept following the children and found something interesting: the farmer children stopped fussing before long and then cried a lot less in general. The forager children, on the other hand, kept crying more than the farmer children long after they had been weaned.

In other words, toddlers intelligently judge their strategies for procuring care from their parents based on their situation. Of course, Dr. Phil could have told them that; it's just how my toddlers behave also.

The question is whether we need "parent-offspring conflict theory" to tell us any of this. It may be that evolution has left human toddlers with a range of sensitivities for crying that they modulate on the basis of environmental input. But I would put it differently from my own experience: toddlers are learning how to communicate with their parents, and they respond to feedback in choosing how to express themselves. Parents who do not respond favorably to tantrums will face fewer of them in the future. From the child's point of view, her developing brain is bootstrapping itself into effectively obtaining what she wants. In this case, I think rationality is a better answer than evolutionary fine-tuning of behavioral responses.