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Aerial view of Newark, NJ.

Humanity has come to dominate and master much of the global ecosystem – especially in the spread of modern cities.

The cities of roads, buildings, rushing cars and teeming sidewalks have created whole new opportunities for evolution, creating niches exploited by bedbugs, pigeons, rats, and other adaptive species, says a new meta-analysis published in Science.

“We’ve created a novel ecosystem that no organism has ever seen before,” said Marc Johnson, a biologist at the University of Toronto Mississauga, one of the authors. “People who don’t believe in evolution need not go (farther) than their backyards to see evidence of it.”

The meta-analysis involved more than 150 studies, almost all of which were published over the last decade.

The impermeable pavement, increased temperatures, and abundance of human food – and human hosts – has led to the rise of diversity among species normally considered pests.

They are “urban exploiters,” and become at least partly “anthrodependent,” write Johnson and his colleague Jason Munshi-South, a biologist at Fordham University.

For instance, bedbugs have made a huge rebound in the years since DDT was banned, and are now spread on public places and on planes throughout the modern world, they write. Cockroaches of various species have also thrived in growing cities worldwide. Head lice have developed better immunity to insecticides, meaning they have refined survival techniques to continue thriving in cities. Mosquitoes in places like the London Underground have evolved to live year-round in the warm air of the subway, and to lay eggs faster without needing to constantly feed on human blood. Even viruses like dengue have refined their survival techniques to spread wider and faster – and survive better – than ever before.

But it also means other species benefit from the urban environment created by humans – and not directly off human bodies.

For instance, the white-footed mice of New York City became distinct from one another based on their isolation in the city’s parks over just a few generations. In Tucson, Arizona, house finches developed longer and wider beaks for stronger bites, since they had come to rely on the hard-shelled sunflower seeds found in local birdfeeders. The crested anoles of Puerto Rico, from a family of reptiles, adapted to have longer limbs and more toes in the cities of the island, for better movement across the hard surfaces of sidewalks and pavement. Killifish in many cities have been documented to evolve tolerance to polychlorinated biphenyls found in polluted city water, they add.

The natural selection of species in artificial environments need not be surprising, considering the growing literature on the subject, the two scientists write.

“It was long thought that evolution was too slow to study on time scales relevant to urbanization, but it is now recognized that evolution can be rapid, with observable evolutionary change in as little as two generations,” they conclude.

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