When next you meet a rat or raccoon on the streets of your city, or see a starling or sparrow on a suburban lawn, take a moment to ask: Where did they come from, so to speak? And where are they going?

In evolutionary terms, the urban environments we take for granted represent radical ecological upheavals, the sort of massive changes that for most of Earth’s history have played out over geological time, not a few hundred years.

Houses, roads, landscaping, and the vast, dense populations of hairless bipedal apes responsible for it: All this is new, and animals are adapting, fast, all around us. A growing body of scientific evidence suggests that the brains and behaviors of urban animals are changing rapidly in response.

“A lot of biologists are really interested in how animals are going to deal with changes in their environments,” said biologist Emilie Snell-Rood of the University of Minnesota. “Humans are creating all these totally new environments compared to what they’ve seen in evolutionary history.”

Snell-Rood is one of many researchers who have updated the conventional narrative of urban animals, in which city life favors a few tough, adaptable jack-of-all-trades — hello, crows! — and those species fortunate enough to have found a built environment similar to their native niches, such as the formerly cliff-dwelling rock doves we now call pigeons and find perched on building ledges everywhere.

The long view, though, is rather more multidimensional. Cities are just one more setting for evolution, a new set of selection pressures. Those adaptable early immigrants, and other species that once avoided cities but are slowly moving in, are changing fast.

As Snell-Rood and colleagues describe in an August 21 Proceedings of the Royal Society B article, museum specimens gathered across the 20th century show that Minnesota’s urbanized small mammals — shrews and voles, bats and squirrels, mice and gophers — experienced a jump in brain size compared to rural mammals.

Read more at Wired.

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