Why dogs have bigger brains than cats

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Being sociable has its advantages, including giving you - or at least your species - a bigger brain. Across more than 500 mammal species, animals that lived in social groups had bigger brains than those that lived by themselves.

Evolutionary biologists had long assumed brain size increased in mammals in a more or less consistent fashion, with each species gaining roughly the same boost relative to body size over time. However, Oxford researchers Dr. Susanne Shultz and Professor Robin Dunbar have revealed in their new study that the truth is a bit more complicated, and it's actually the sociability of a given species that determines brain size.

Unsurprisingly, primate brains grew the most over time, followed by horses, dolphins, camels, and dogs. All these creatures tend to live in stable social groups. Solitary mammals, including everything from cats to rhinos, showed much slower brain size growth over the same evolutionary period. The researchers believe this means being sociable requires an increase in brainpower to deal with all the new challenges that brings.

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Dr. Shultz explains:

"This study overturns the long-held belief that brain size has increased across all mammals. Instead, groups of highly social species have undergone much more rapid increases than more solitary species. This suggests that the cooperation and coordination needed for group living can be challenging and over time some mammals have evolved larger brains to be able to cope with the demands of socialising."

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Her fellow researcher Professor Dunbar says it's particularly interesting that cats still have relatively small brains, despite the stimulating company they keep:

"For the first time, it has been possible to provide a genuine evolutionary time depth to the study of brain evolution. It is interesting to see that even animals that have contact with humans, like cats, have much smaller brains than dogs and horses because of their lack of sociality."

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[PNAS]