New study reveals dominant force determining Evolution on Earth today

(ORDO NEWS) — A growing body of evidence suggests that humans are currently the main driving force behind evolution on Earth. From selective breeding to ecological modification, we are changing so much of our world that we now not only determine the climate, but the direction of life itself.

Now, in a massive project involving 287 scientists from 160 cities in 26 countries, researchers have studied how urbanization has affected evolution on a global scale. They used white clover (Trifolium repens) as a model, a plant native to Europe and Western Asia but found in cities around the world.

“There has never been a field study of evolution on this scale or a global study of how urbanization affects evolution,” said evolutionary biologist Mark Johnson of the University of Toronto Mississauga (UTM).

Collecting more than 110,000 samples along gradients that stretched from cities, through suburbs, to the countryside, they found that clover in cities now resembles clover in another city located in another world rather than clover in nearby farmlands or in forests, regardless of climate.

This is an example of parallel adaptive evolution – when separate populations are formed under the influence of the same selective pressure on certain traits in different places.

This shows that the ways in which humans modify the environment have a greater influence on the formation of these traits than natural phenomena such as the genetics of local populations and climate.

While urbanization apparently shares many common features around the world, it has not yet been established that they act together to push evolution in the same direction.

“We’ve just shown that this is happening, often in a similar way, on a global scale,” said UTM environmentalist James Santangelo.

“For urbanization to promote parallel evolution, urban areas must converge in ecological characteristics that affect the fitness of an organism,” the researchers explain in their paper.

Taking a closer look, the international team determined that one of the characteristics that varies from urban to rural areas is the plant’s production of hydrogen cyanide. White clover uses this chemical as a defense mechanism against its herbivorous predators. It also helps them resist drought.

Plants in the most remote rural communities were 44 percent more likely to produce hydrogen cyanide than plants in city centers. It appears that grazing contributes to the production of more hydrogen cyanide in rural areas than in cities where grazing pressure is not as strong; in the absence of this pressure, drought becomes a driving factor.

This happened despite strong gene flow between white clover populations along each gradient, which means levels of this chemical are strongly selected, over and over again.

We have already disrupted the natural size spectrum of animals in the ocean, partly through the selective removal of large fish by fishing, leaving more fish with small fish genes for generations to come. Many fish are now 20 percent smaller and their life cycles are 25 percent shorter on average.

The unforeseen consequences of our actions also change the shape of the birds. “The wingspan of shore swallows has evolved to be smaller near roads, and killed swallows have longer wings, consistent with selection for increased maneuverability in traffic,” explained zoologist Sarah Otto in 2018.

These latest results are another example of a clear urban signal in evolution. Research has already shown that the rate of evolutionary change is higher in urban landscapes compared to natural and non-urban human systems.

This is the strongest evidence we have that we are changing the evolution of life in [urban areas].” In addition to ecologists and evolutionary biologists, this will be important for society,” says UTM biologist Rob Ness. Especially when you consider that by 2030 the amount of urbanized land will triple compared to the year 2000.”

The researchers have amassed a large database that they can now continue to explore for human influence on clover evolution. By better understanding how we accidentally set such changes in motion, we are more likely to intentionally take the helm and direct evolution in a more conscious and safer way.

“This knowledge could help conserve some of Earth’s most endangered species, mitigate pest impacts, improve human well-being, and contribute to the understanding of fundamental ecoevolutionary processes,” the authors conclude.

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