Urban creatures found to have bigger brains than their country cousins.

A U.S biologist has found human behaviour could be driving the evolution of animals’ brains by changing the habitats in which they live.

The research suggests the brains of some animals have got bigger in tandem with the industrialisation of their habitat – making some city animals smarter than their rural peers.

Evolutionary biologist Emilie Snell-Rood discovered white-footed mouse and meadow voles living in cities, had on average brains that were six per cent larger than the brains of animals collected from farms in the countryside.

Associate Professor Snell-Rood, of the University of Minnesota’s College of Biological Sciences, believes animals are showing ‘complex cognitive responses to both urban and rural areas with cranial capacity tracking human-induced change in some cases’.

She is interested in whether small animals will be able to cope with the conversion of prairies to agriculture or forests being replaced by cities to ultimately cope with human-induced change.

Previous research found a link between brain size and the ability to adapt to urban environments in birds, but did not investigate whether the change of environment caused the evolution.

Together with undergraduate student Naomi Wick, Professor Snell-Rood set out to find ‘if dealing with a new environment is just a matter of species sorting – in which a particular species is “pre-adapted” for success in a particular environment – or actually changes going on within species in addition to that species-level variation’.

The researchers examined specimens from the Bell Museum of Natural History collections dating back to the early 20th Century, focusing on the cranial capacity of 10 species, including varieties of shrews, voles, bats, and squirrels, along with a mouse and gopher, from locations in and around the Twin Cities metro.

They found the urban populations of two of the species did, in fact, possess significantly greater cranial capacity and predicted that if cleverer animals thrived in urban environments, cranial capacity should also increase over time.

The white-footed mouse and meadow voles living in cities, had on average brains that were 6 per cent larger than the brains of their peers collected from rural habitats.

While the researchers can’t say for certain whether the changes are evolutionary or developmental, evidence suggests the former.

‘We tended to not see changes in body size which suggests it’s not just nutritional, but rather an evolutionary response,’ said Professor Snell-Rood. 

She said the study ‘reminds us of the fact that populations adapt, and that at least some species are tracking human-induced environmental change.

However, some of the specimens examined contradicted her theory.

‘We didn’t see cranial capacity increases over time in the urban specimens…and actually, for two species we see a decline over time, while the bats and shrews show an increase in cranial capacity in rural populations.’

Professor Snell-Rood said: ‘Neural tissue is incredibly expensive metabolically. There are trade-offs in investing in brains and investing in reproduction, which may be why we see a reduction in cranial capacity over time in two of the species – larger brains may be favored just during the initial colonisation of the city.’

She thinks humans are changing rural environments in ways that could be just as challenging as cities, resulting in the changes in cranial capacity over time seen in bats and shrews.

Daily Mail Science