Simon Makin in Scientific American:
Other species are capable of displaying dazzling feats of intelligence. Crows can solve multistep problems. Apes display numerical skills and empathy. Yet, neither species has the capacity to conduct scientific investigations into other species' cognitive abilities. This type of behavior provides solid evidence that humans are by far the smartest species on the planet. Besides just elevated IQs, however, humans set themselves apart in another way: Their offspring are among the most helpless of any species. A new study, published recently in Proceedings of the National Academy of Sciences (PNAS), draws a link between human smarts and an infant’s dependency, suggesting one thing led to the other in a spiraling evolutionary feedback loop. The study, from psychologists Celeste Kidd and Steven Piantadosi at the University of Rochester, represents a new theory about how humans came to possess such extraordinary smarts.
Like a lot of evolutionary theories, this one can be couched in the form of a story—and like a lot of evolutionary stories, this one is contested by some scientists. Kidd and Piantadosi note that, according to a previous theory, early humans faced selection pressures for both large brains and the capacity to walk upright as they moved from forest to grassland. Larger brains require a wider pelvis to give birth whereas being bipedal limits the size of the pelvis. These opposing pressures—biological anthropologists call them the “obstetric dilemma”—could have led to giving birth earlier when infants’ skulls were still small.
Thus, newborns arrive more immature and helpless than those of most other species. Kidd and Piantadosi propose that, as a consequence, the cognitive demands of child care increased and created evolutionary pressure to develop higher intelligence. This in turn led to larger brains, requiring earlier birth—and that produced offspring who were more helpless, requiring even higher parental intelligence, a circle that led to “runaway selection” and superintelligent modern humans. “We were playing with my niece, thinking, ‘It takes a lot of human abilities to take care of this kid,’” Piantadosi says. “You have to figure out what they need, and when.” You also have to understand goals, Kidd adds: “If the goal is to grab at something in a dangerous location, being able to read that quickly is very useful.” Humans are particularly good at this kind of social reasoning and various theories have been suggested to explain this, usually involving living in social groups. “Our theory is an alternative, which says that social reasoning evolved to take care of kids.” Piantadosi says.