Cities drive natural selection

The same evolutionary mechanisms identified 150 years ago by Charles Darwin are active within the world’s great cities and should no longer be ignored, say the guest editors of an influential science journal.

Marc Johnson, James Santangelo and Ruth Rivkin from the University of Toronto Mississauga in Canada, at the helm of the Proceedings of the Royal Society B, present 15 papers that together demonstrate that cities constitute “agents of change”, significantly influencing natural selection across a wide range of species, from owls to Daphnia water fleas.

“It’s pretty remarkable,” says Johnson. “For years, biologists ignored cities, seeing them as ‘anti-life’, and only recently biologists began to realise that cities are agents of change, driving evolution of organisms living around us and even some living on us.”

The picture to emerge from the research included in the special edition of the journal finds three powerful trends at work in cities: big urban centres frequently alter evolution by natural selection; species across the biological spectrum are adapting to city environments; and many of those species are evolving to live alongside humans.

One paper included in the collection outlines adaptive differences that have arisen between rural and urban populations of Daphnia water fleas – a common zooplankton found in abundance in lakes, rivers and ponds.

Kristien Brans and colleagues from Leuven University in The Netherlands took populations of the organism from rural and urban areas and tested their resilience to water temperature. They found that urban Daphnia were much better able to handle higher temperatures – typical of cities – than their country-living cousins.

At the other end of the biological complexity scale, burrowing owls (Athene cunicularia) in South America have also been evolving to better withstand the pressures of city life. German researchers led by Jakob Mueller from the Max Planck Institute of Ornithology discovered that populations of the owl living in different cities had developed similar genetic responses to environmental stimuli – even though there was no cross-breeding between them.

“Understanding how cities shape the evolution of urban populations can facilitate designing management strategies for urban pests and help minimize the impact of humans on the spread of invasive species,” says Johnson.

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