Whales evolved large brains in the same way that we did – New Scientist News

By Colin Barras

Tony Wu / Nature Picture Library / Science Photo Library

The largest brains ever to have evolved belong to whales. Now we have discovered that the marine mammals gained their big brains size in the same way we did through massive expansion of two particular brain regions, fuelled perhaps through changes in diet.

Amandine Muller at the University of Cambridge and Stephen Montgomery at the University of Bristol, UK, looked at brain size data from 18 species of whale and dolphin, as well as from 124 different land animals including 43 species of primate. With few exceptions, the whales, dolphins and primates all seem to have gained large brains through dramatic growth of the same two brain regions: the cerebellum and neocortex.Both regions are important for cognitive functions such as attention, and for controlling the movement of the body.

It makes sense that the cerebellum and neocortex evolve in unison, says Montgomery, because they are physically connected by many brain pathways. Its possible one can only change so much without being constrained by the performance of its partner, and needing the other structure to catch up, he says.

But what drove these two brain regions to expand so dramatically in whales and dolphins? Muller and Montgomery first explored whether the trigger was a change in social behaviour. In common with some primates including our species whales and dolphins can form complex social groups. However, the two researchers found no strong correlation between the whale and dolphin species with the most advanced social behaviour and those with a particularly large cerebellum and neocortex.

But they did discover that the whale and dolphin species with a larger cerebellum and neocortex typically enjoy an unusually broad diet, in terms of the variety of foodstuffs they consume. This might suggest that broadening the diet encouraged the evolution of larger brains.

It is unclear why diet and brain size are linked. Montgomery speculates that a broad diet is more likely to provide the energetic resources needed to fuel brain expansion. Alternatively, it might be that marine mammals with a broader diet need to learn and use a wider range of foraging behaviours to exploit different food resources. This could require a larger brain.

Unravelling how and why brain evolution and diet are linked in whales and dolphins could be important because it might help us understand why primates evolved large brains too.

Many researchers argue that primates gained large brains as their social worlds became more complex. But in the last few years, some have given up on this social brain hypothesis because of evidence that primate brain expansion is actually better explained by changes to diet. The data from whales and dolphins provides new evidence to bolster this idea.

Journal reference: Journal of Evolutionary Biology , DOI: 10.1111/jeb.13539