Urbanization May Be Pushing Evolution to a Tipping Point

That humans and the cities we build affect the ecosystem and even drive some evolutionary change in species’ traits is already known.

Spiders in cities are getting bigger and salmon in rivers are getting smaller; birds in urban areas are growing tamer and bolder, outcompeting their country cousins.

What’s new is that these evolutionary changes are happening much more quickly than previously thought, and have potential impacts on ecosystem function on a contemporary scale. Not in the distant future, that is — but now.

A new paper by Marina Alberti of the Univ. of Washington College of Built Environments’ Urban Ecology Research Lab published this month in the journal Trends in Ecology & Evolution suggests that if human-driven evolutionary change affects the functioning of ecosystems — as evidence is showing — it “may have significant implications for ecological and human well-being.”

Alberti, a professor of urban design and planning, said that until recently it was assumed that evolutionary change would take too long to affect ecological processes quite so immediately. Such thinking has prevented evidence from coming together “in a way that can only emerge through a cross-disciplinary lens,” she said, observing the interactions between humans and natural processes.

“We now have evidence that there is rapid evolution. These changes may affect the state of the environment now. This is what’s called eco-evolutionary feedback.

“Cities are not simply affecting biodiversity by reducing the number and variety of species that live in urban habitats,” Alberti said. Humans in cities are causing organisms to undergo accelerated evolutionary changes “that have effects on ecosystem functions such as biodiversity, nutrient cycling, seed dispersal, detoxification, food production and ultimately on human health and well-being.”

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