There is a type of mosquito that lives in the London Underground. This particular breed of mozzie has evolved to survive its subterranean habitat. Unlike its above-ground relatives, it doesn't hibernate in winter or require blood to make eggs. In fact, the two mosquitoes are so genetically different that they can no longer interbreed.
Meanwhile, in Tucson, Arizona, house finches have adapted to have longer, wider beaks because it makes it easier for them to munch on all the delicious treats in people's backyard birdfeeders.
In both cases, evolution has been driven by human activity and, more specifically, urbanization.
"Traditionally, we've thought about evolution as a long-term process driven by environmental pressures and the interactions between species. But now there is a new driver that is rapidly changing many other species, which is how they interact with humans and our built environment", Jason Munshi-South, associate professor of biological sciences at Fordham University, explained in a statement.
"Humans and our cities are one of the most dominant forces of contemporary evolution now."
In a paper published in Science this week, Munshi-South and Marc Johnson, an associate professor of biology at the University of Toronto Mississauga, analyzed existing research on urbanization's effect on evolution to synthesize their results. They found that cities are causing evolution to accelerate.
Animals are, through natural selection and random mutations, adapting to pesticide use, pollution, local climate, and the structure of cities. And it's all happening at a much faster rate than you would normally expect.
"We've created a novel ecosystem that no organism has ever seen before," Johnson said.
"It's good news that some organisms are able to adapt, such as native species that have important ecological functions in the environment. But it can also be bad news that the ability of some of these organisms to adapt to our cities might increase the transmission of disease.”
“Bedbugs, for example, were scarce two decades ago, but they've adapted to the insecticides used to keep them at bay and have exploded in abundance worldwide," he added.
The pair also discovered that animals in cities show less genetic diversity than ones in less urban areas. Take, for example, the red foxes that have recently migrated to Zurich in Switzerland. They show less genetic diversity than those in nearby rural regions, which, the researchers say, could put them at greater risk from disease and climate change.
The pair hope that by drawing attention to urbanization's effect on evolution, city planners can be "kinder to ourselves and the environment" and find ways to protect native species while limiting the spread of disease-carrying pests.