Are Big Brains a Big Burden for Mammals?

May 13, 2016 | Erica Tennenhouse

Beluga whale (Delphiapterus leucas)
Photo credit: Steve Snodgrass/Wikipedia (CC BY 2.0)

Brain size may set some species on a path to extinction.

Brain size is a bit of a balancing act. Big brains offer species the ability to cope with challenges through behavioral flexibility and innovation, but those with large, calorie-hungry brains must pay a high energetic cost. The benefits have always seemed well worth the price — over the past millions of years, mammal brains have been getting bigger and bigger.

But researchers have found that many species can no longer afford their big brains. Their study, which will soon appear in the journal Evolution, revealed that as brain size increases, so does a species’ risk of going extinct.

The link between extinction risk and brain size was not direct. Rather, the study indicated that the vast amount of energy consumed by the brain makes it challenging for females to produce big-brained offspring.

SEE ALSO: Fast Metabolism Gave Humans Bigger Brains

As study lead author Alejandro Gonzalez-Voyer, an assistant professor at the National Autonomous University of Mexico, explained in an email to The Science Explorer, “females of larger-brained species invest in fewer offspring per reproductive period, and offspring take longer to develop, both within the womb and after birth.” These effects of brain size remain even after accounting for the effects of body size.

Many mammals today are constantly encountering new threats — such as changing climate and habitat loss — to which they need to be able to adapt quickly. Because adaptation is something that occurs over generations, being slow to reproduce “does not enable [species] to bounce back after disturbance, or limits their resilience,” said Gonzalez-Voyer.

As the authors conclude, “In today’s world the once beneficial large brain has apparently become a burden for many mammals”

But this does not appear to be the case for the largest-brained mammal of all — humans, whose populations are soaring higher than ever. “It is possible that the relationships between brain size and “success” is non-linear,” suggests study co-author Manuela Gonzalez-Suarez from the University of Reading. “This means that the costs of a big brain can outweigh the benefits up to one point at which the social complexity and innovation capacity becomes so great that again the scale is tilted towards the benefits (like in humans).”

For those falling below the threshold, the study suggests that big brains are an excessive weight on the shoulders of many species. And this insight may actually offer some relief. As Gonzalez-Suarez explains, “Conservation funds are limited and managers and policy makers need to make decisions constantly about where to invest.” With the knowledge that species with larger brains are at greater risk of extinction, the authors can now recommend that greater resources be invested in the protection of those species.

She adds: “This is of course a simplification but the idea is that we can start creating ways to categorize risk and prioritize conservation investment.”

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