Dr. Snell-Rood proposes that the brains of all six species have gotten bigger because humans have radically changed Minnesota. Where there were once pristine forests and prairies, there are now cities and farms. In this disrupted environment, animals better at learning new things were more likely to survive and have offspring.

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Studies by other scientists have linked better learning in animals with bigger brains. In January, for example, researchers at Uppsala University in Sweden described an experiment in which they bred guppies for larger brain sizes. The big-brained fish scored better on learning tests than their small-brained cousins.

Animals colonising cities and towns have to learn how to find food in buildings and other places their ancestors hadn’t encountered.

“We’re changing rural populations, too,” Dr. Snell-Rood said. As forests get cut for timber or farming, for example, bats may have to travel farther to find food and still be able to navigate home to roost. Big brains may have benefited them as well.

Other scientists not involved in the research hailed it as the first report of significant changes in brain size in animals outside labs. “I think the results are exciting and deserving of much follow-up work,” said Jason Munshi-South, an evolutionary biologist at Fordham University.

Dr. Munshi-South and other researchers see a need to test Dr. Snell-Rood’s hypothesis in new ways, so as to rule out alternative explanations.

If she’s right, for example, then the same trend she observed in Minnesota should exist in museum collections of skulls from other heavily developed regions of the world.

It should also be possible to continue the research in labs, by breeding small-brained rural mammals with their big-brained cousins. By studying their offspring, scientists could study the genes involved in producing different brain sizes. They could even give the animals tests to see just how much life in a human-dominated world has changed how their brains work.

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But the ultimate breeding experiment to test Dr. Snell-Rood’s hypothesis may not be possible outside the movie set for “Jurassic Park.” “What would be really cool would be to raise populations from 1900,” said Dr. Snell-Rood with a laugh, “but we can’t really do that.”

This article originally appeared on New York Times.