Environment May Not Be An Important Factor In Size

Humans, specifically Homo sapiens, have entrenched themselves at the top of the food chain, something most people take for granted and ascribe to the powers of the human brain. But for all that, scientists don’t really understand why our brains evolved to be as large and powerful as they are.

A popular theory, which has been around for a long time, is called the cognitive buffer hypothesis, and it says large brains evolved to deal with fast or unexpected changes to the environment, thereby helping with survival. In other words, a variable environment would lead to larger brains among species that live there. But it is difficult to verify this theory using humans, since us modern humans are the only survivors of the Homo genus, and we have nothing to compare with.

On the other hand, birds — the only extant dinosaurs — have been around since long before the Homo genus itself came into being. And given how diverse and plentiful they are the world over, and with a wide range of brain sizes, they are also great candidates for testing the cognitive buffer hypothesis.

Carlos Botero, an assistant professor at Washington University in St. Louis, had done precisely that in an earlier study which seemed to support the hypothesis. In that study, Botero found mockingbirds who lived in variable habitats had more complex songs, which could be linked to learning ability and hence brain size. But his study showed no link between more elaborate birdsong and survival, leading him to conduct a new study.

Published Monday in the journal Nature Ecology and Evolution, the study — conducted by Botero, a postgraduate associate at the university Trevor Fristoe, and biologist Andrew Iwaniuk of University of Lethbridge, Canada — found large brains were not more likely to evolve in variable habitats, compared to stable habitats. But it did show that birds with larger brains could successfully inhabit a broader range of environments.

Professor Steve Gentleman poses with a human brain at the Multiple Sclerosis and Parkinson’s UK Tissue Bank at Imperial College London, June 3, 2016. Photo: Reuters/Neil Hall

“The findings were pretty surprising. In the first part of the study, we showed that a big brain really does give birds a survival advantage in variable environments. So the mechanism works. But that made it all the more puzzling when the second part of the study showed that big brains often evolved in stable — not in variable — habitats,” Fristoe said in a…

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