Urbanization has long driven change in human societies, but it also has an impact on plants and animals too, and not just in taking away land for their use. Other organisms that live in cities have been evolving way to cope with the concrete jungle just as they would the regular jungle. While it’s obvious that birds and rats have adapted to city life, there are much more subtle changes too.
The common white clover grows all over the place, and it has an interesting defense against herbivores: it releases poison when crushed to keep herbivores from eating it. But when the plants freeze, this same poison can harm them, so plants in colder climates make less of it. Because we know that cities are warmer than surrounding areas, scientists figured that urban white clovers would have less poison, but they found the opposite to be true.
What happens is that snow, which generally falls more and sticks around longer in rural environments, insulates the ground, so that plants under snow are actually warmer than those exposed to air. So while air temperatures in cities are warmer than those of rural areas, the ground is actually much colder. Scientists have begun referring to this as the “urban cold island effect.” That cold means the clovers are more prone to freezing and they have less poison as a result.
While this is a pretty amazing discovery and certainly interesting, it’s not going to “change the world” all that much. But science isn’t all Earth-shaking discovery, a lot of it is building upon other information to gradually discover something huge. What the white clover is telling us, though, is that there is a lot we don’t know about urban ecosystems and climates that can impact the evolution of organisms in urban environments. And it tells us that there are probably better ways to manage climates and ecosystems in urban environments to improve the lives of all organisms there, human or otherwise.