Why domestic cats may have small brains

Domestic cats have smaller brains than their wild ancestors. Smaller brains need less energy. Cats might thus be able to spend more energy on other energetically costly organs. In the scientific journal Integrative Biology, a group of international researchers suggest that domestic cats have used this energy to enlarge their gut length to adapt their digestive system to the human environment.

That domesticated wild animals such as pigs, cats and dogs have relatively smaller brains than their wild ancestors is well documented. This is part of ’the domestic syndrome’, along with floppy ears or shorter snouts. Scientists around the world are still puzzled by what causes the reduction in a cat’s brain size during domestication.

Cats changed their diet

In the scientific journal Integrative Biology, an international group of researchers elaborate on the possibility that domestic cats have changed their diet from strictly rodents and birds into a more starch-rich diet, leftovers of bread, for instance. ’To digest this kind of food, cats simply need more time and therefore a longer gut’, says Associate Professor Alexander Kotrschal of Wageningen University & Research, the study’s senior author.

Kotrschal and his colleagues establish two processes, which may or may not be linked. First, to better digest their changed diet domestic cats might have increased their gut length. This investment could have made it necessary to divert energy from the brain to the digestion system, thus explaining the relatively smaller brain of domestic cats compared to wild cats.

Second: the human environment with readily available food causes a relaxed selection pressure on brain size. Domestic cats likely need not be as clever as their wild ancestors to survive. This allows domestic cats to invest the surplus of energy somewhere they need it more: in the gut.

Gut-size versus brain-size

The relationship between the gut and the brain has long been hypothesized and experimentally shown. In 2013, Kotrschal and colleagues used artificial selection on large and small brain sizes over several generations of guppies. Indeed they found that evolving a larger brain meant decreasing gut size and vice versa. This was the first evidence of a gut-size versus brain-size trade-off. Similar processes may be at work during domestication.

Kotrschal: ’Domestic cats do not need their brain that much anymore, simply because they do not need to search for food. This might have relaxed the selection pressure on brain size’.

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