Why are our brains so big, anyway – dead things dead things gas 78 industries


For years, researchers have puzzled over why our noggin-embiggening occurred: Big brains are, after all, costly to feed. One leading theory held that our brains increased in size to manage the cognitive demands of ever-more complex communications and other social processes. New research suggests, however, that interactions with each other played only a small role compared with the big driver of bigger brains.

It’s a strange supersizing, evolutionarily speaking: Brains require a lot of energy, which means a lot of resources, and the expanse of the stuff between our ears likely stunted our body size. Our brains also grow at a rate faster than our bodies — the human brain typically reaches maximum size around the age of ten years, long before the body attains its full height or reaches sexual maturity.

As anthropologist and evolutionary ecologist Richard McElreath, commenting today in Nature on the new study, puts it: “Brain growth is not given priority in this way in other apes, and the human pattern is puzzling because it keeps our bodies smaller, more vulnerable and less productive for longer. The answer to this riddle must lie in how the human brain helped our ancestors survive and reproduce.”

For many, the leading candidate was the social-intelligence model: Our complex social interactions of competition and collaboration require a tremendous amount of brain power. The ecological-intelligence model, however, held that our most basic needs, such as finding food while not becoming food in the process, drove us to have ever bigger brains.

The authors behind the new study set up a computational model that takes into account when, in the typical life, key parts of a human — specifically the brain, reproductive tissue and body size — require increased resources to develop. For example: An increase in brain size leads to an increase in skill, but an increase in body size makes it easier for the individual to use that skill to acquire more energy.

It’s a trade-off, in other words, and the complex model designed by the researchers generated different scenarios that could explain different brain-to-body-size ratios and, at last, reveal the most plausible reason we’re running around with such big brains.

The study considered four different kinds of challenges: between-individual competitive (me against you), between-group competitive (us against them), ecological (me against nature) and cooperative ecological (us against nature). In the scenarios run through the model, the challenges were weighted in different combinations until one emerged as the most likely to explain our big brains.

Probably surprising to anyone who’s ever rooted against the home team or waded into a political discussion on Facebook, the researchers found that the most likely model driving big brain evolution was only ten percent between-group competition. Cooperation appears to account for an additional 30 percent of the push for brain-embiggening.

The main driver of increased brain size, accounting for 60 percent of the demand, seems to be meeting the ecological challenges our species faced — though this is perhaps less of a surprise to fans of “Running Wild with Bear Grylls,” the old “Survivorman” and similar shows.

Today’s study appears in Nature. In his accompanying News & Views commentary, McElreath notes the research is neither perfect nor complete. It did not consider, for example, the cultural intelligence hypothesis, nor can the findings be applied to the evolution of intelligence outside of our own species. It’s a start, however, and it creates a new methodology for approaching this complex question.