Urbanisation’s Impact On Evolution: Can Smart Planning Lead To Its Reversal?


It all started with a moth

Anyone who remembers the case of the peppered moth from high school biology probably won’t be surprised to hear that human activity can impact a species’ evolution. For those who missed it or are otherwise in need of a refresher, the story harkens back to the early days of the industrial revolution. From Manchester to London, soot from coal-burning was wreaking havoc on air quality. As the dust settled on every surface imaginable, things started to get… well, dirty. Even tree trunks darkened. And tragically for the usually light-colored peppered moth, this meant it suddenly became a lot easier to spot. Much to the delight of hungry birds.

And that’s when evolution stepped in. Through a previously rare genetic mutation, moths that sported dark, soot-colored wings were better able to avoid being gobbled up and soon they began to outbreed their “normal” light-colored brethren. Biologists started tracking the phenomenon, studies were written, and before you knew it, our friends the moths were famous. Decades later, as coal passed out of vogue and the air got cleaner, darker moths found themselves sticking out against surfaces that were no longer covered in soot. And then it was time for the fairer moths to have a biological party.

A similar evolutionary event was noted in 2008, when it was discovered by researchers in France that a plant called hawksbeard (Crepis sancta) had adapted to an urban environment by changing the size of its seeds. Of course the plant didn’t do this consciously. (It’s a plant, after all.) But plants that produced smaller, lighter seeds saw them swept away by the wind, only to land on impenetrable concrete. Whereas heavier, less aerodynamic seeds just plopped down right next to their parent plant – i.e. in the soil – and were able to germinate and grow. Thus the trait of producing heavy seeds was passed on to the next generation of city-dwelling hawksbeard plants.

We stand at the dawn of the Anthropocene era

While these seemingly harmless examples of human impact on individual species’ traits may be interesting and even amusing, they reflect a growing trend that is altogether more ominous. The latest study in this vein, a global analysis of more than 1,600 recorded trait adaptations, shows that rates of evolutionary change are greater in urban environments than in natural or non-urban environments.

It’s not only flora and fauna who will suffer the ultimate effects. Rather, as we enter a new Anthropocene era, every living creature on the planet will be affected – we urban-dwelling Homo sapiens will be no exception. Ecosystem change will impact critical survival factors such as food production and the spread of infectious disease. According to the study’s co-author, Marina Alberti, a professor at the University of Washington’s Department of Urban Design and Planning, urbanization has been a catalyst for species change. “We are changing the evolution of Earth,” she told the BBC.

City planners to the rescue

What, if anything, can city planners do to mitigate the disruption of urbanization on ecosystems? Organizations like Urban Hub – an interactive online platform – are tackling exactly those questions. Exploring solutions such as green walls and rooftop gardens, improving public transport, and switching to “lean” manufacturing is proving to be important areas of enquiry.

In addition to being generally inhospitable to some animals and plant life, cities that are primarily covered in concrete suffer from numerous environmental consequences. Concrete absorbs heat during the day and releases it at night. Heat also becomes trapped between the densely packed buildings of city centers. Further, many cities have too few mature trees to absorb carbon dioxide, produce oxygen, and provide shade. All of these are contributing factors to the well-known “urban heat island” effect. This means that city temperatures can be anywhere from 1 to 5°F warmer than surrounding rural areas during the day, and as much as 22°F warmer at night. These warmer temperatures in the summer lead to increased demand for energy, further exacerbating the accumulation of greenhouse gases.

That’s why solutions like the aforementioned green walls play such an important role in helping to improve city ecology. Incorporating plants into building exteriors not only adds aesthetic value, it also has a cooling effect that lowers energy demands. Of even further benefit are city parks, providing not only tree cover and shade, but also recreational opportunities. The more city ground covered by grass rather than pavement, the better for groundwater systems and air quality.

Pollution from traffic gridlock is also a problem for many cities, notoriously so in cases such as Los Angeles, where public transportation is almost non-existent. Even cities with well-developed public transportation struggle with heavy traffic. London incorporated a congestion charge to address the problem and other cities have followed suit. Major car manufacturers such as Toyota and Volvo are taking measures to phase out gas engines in favor of electric and both France and the UK have said they will place a ban on new gas or diesel cars after 2040.

So, what could all of these innovations mean for city wildlife? As we’ve seen with the peppered moth, when environmental conditions improve, evolutionary changes can indeed reverse course. So here’s to the return of smaller, lighter hawksbeard seeds… may our future city greenspaces be hospitable landing spots for them.

About the Author Staff Writer

Our writers come from all over the world, but one thing unites them - their passion for sustainability.

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