Piantadosi, S.T. and Kidd, C. (2016). Extraordinary intelligence and the care of infants. Proceedings of the National Academy of Sciences, 113 (25), 6874-6879.
Dunsworth, H.M. (2016). Thank your intelligent mother for your big brain. Proceedings of the National Academy of Sciences, 113 (25), 6816-6818.
In their analysis, Piantadosi and Kidd argue that there is a feedback loop in evolution between intelligence and having helpless babies. The basic idea is that when a brain is large, it takes a lot of space and a lot of energy, and so pregnancies cannot sustain the entire development of the baby. As a result, larger brained animals are born earlier in brain development, and therefore are born more helpless. However, helpless babies are difficult and complicated to care for, and require more intelligent parents to raise them. As a result, the two create a feedback loop resulting in “runaway selection” for ever larger brains: larger brains mean better able to care for young, but also that the young have to be born earlier in development, requiring even brainier care.
Using length of time until weaning as a measure of helplessness, they find a connection between helpless infants (altriciality) and brain size among primate and other species. They also acknowledge that in a complex system, it is unlikely that one causal path explains everything. However, a few interesting ideas come out of this construct. First, they make the point that no other species can care for a human infant due to the complexity of care required; as they point out, there is no record of a feral child being taken care of by a non-human animal from infancy. In theory, the idea of any other animal being able to care for a newborn baby does seem unlikely. Human babies are remarkably difficult to care for, and have no chance of survival without adequate care. Perhaps it is a relief for parents to know that raising children is supposed to be difficult. It is a key reason why we are intelligent; this implies that it may be the hardest thing we have to do!
Another interesting idea has to do with social intelligence. Piantadosi and Kidd consider whether need for complex social intelligence may be in part due to the need for parents to be able to read the cues of the helpless infants. Infants depend on their caregivers to understand and meet all of their needs. While there are likely many pressures that encourage the evolution of social intelligence, it is credible that child care was one of them. Putting the parent-child relationship and the emotional communication that occurs between them in the center ties in with all the research on attachment and evolution, as well. The primary attachment relationships allow the parents to learn to understand their children and allow the children to learn to understand their parents. That communication happens along multiple channels (visual and auditory, possibly also sensory and even olfactory) and requires hefty brain power to process.
In a commentary on this study, Dunsworth points out that there are many evolutionary models that provide explanations for the link between intelligence and underdeveloped birth. However, she makes the point that, unlike many other species with longer weaning times, human infants continue to require extensive care and feeding even beyond weaning. That, combined with the higher caloric needs of humans in general, means that parents have to work harder to care for children even after they have weaned; many of the technological advances of early humans may have benefited children the most, in that they provided more calories that were easier to digest. In other words, not just our brain size, but even our technological advances may have been motivated in part by caring for our babies. As she puts it, “Perhaps hominid babies have cleverly manipulated their intelligent caregivers into relaxing selection on many of the traits that would benefit survival if they were not born into such a handy and intelligent species” (p. 6818).