It’s easy to overlook the fact that we’re conducting a massive planetary experiment. No species before ours has ever been able to claim such disproportionate shares of the resources that make Earth a living planet, from biomass to fertile land, from the flow of carbon and nitrogen to fresh water.
We are ecosystem engineers on a megalomaniac scale, which means that an essential element of the environment of other species, to which they have scrambled to adapt, is the human presence itself, especially in the very weird clusters of concrete, asphalt and people we call cities. And the rule is clear: in circumstances like these, Darwin enters the field and natural selection goes to work.
Consider, for example, the simple white clover (trifolium repens), a herbaceous plant, native to Eurasia and a member of the family of beans, broad beans and peas. As with so many other Old World plants, white clover hitchhiked on caravels and steamships and colonized the rest of the world, including Brazil. This smaller-scale unconscious experiment, which is part of our immense planetary experiment, allowed scientists to analyze how life in urban environments is able to shape the evolution of a plant species.
The results were recently published in the specialized journal Science, one of the most important in the world. Researchers from 26 countries, including professors from three Brazilian universities, mapped the differences between city and rural clovers and discovered that, around the world, an intriguing parallel evolutionary process is affecting many of the plants that ended up becoming urbanoids. .
It turns out that, like many other vegetables, clovers often produce toxic substances, a method created to prevent herbivorous animals from continuing to chew them. In this species, two separate stretches of DNA serve as a recipe for the production of HCN (hydrogen cyanide), a poison that is also manufactured by humans.
“The ability to produce HCN also increases the tolerance of plants to water stress [falta d’água]”, says Fabio Angeoletto, professor at UFMT (Federal University of Mato Grosso) and co-author of the research.
Angeoletto participated in the study alongside colleagues from Unesp and the Federal University of Santa Maria (RS) — the city of Rio Grande do Sul, by the way, was one of the places where plants were collected in Brazil, along with Curitiba. In nearly half of the places around the world, however, researchers have found that urban white clovers carry mutations that turn off genes linked to HCN production. In rural areas, on the other hand, the presence of plants in which these genes are still functional is much more common.
The explanation is that, with little vegetation, cities have far fewer herbivores. With this, the clover organism does not need to spend energy producing the venom — except in very dry places, where the other function of HCN continues to justify the investment.
The most interesting thing is that all this seems to have happened in parallel, in the most different places. “The center of Tokyo, in this aspect, is more similar to the center of Toronto, Canada, than to the Japanese countryside next door”, says the Brazilian researcher.
Note that this is just a biochemical aspect of a single species. Thousands of other similar phenomena must be happening right now in cities all over the world, in the Darwin gardens that surround us.
