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Scientists have identified a huge driving force of evolution worldwide

By: April Carson

Scientists have long known that evolution is a powerful force, but a new study has identified just how large a role it plays across the globe.

Evidence suggests that humans are now a major force in the evolution of Earth's inhabitants. We're changing so much of our planet, from selective breeding to environmental modifications, that we're not only driving the climate but also directing evolution itself.

Researchers have used white clover (Trifolium repens) as a model – a plant native to Europe and west Asia, but found in cities all around the world - to study how urbanization has impacted evolution on a worldwide scale. They investigated how human settlement has affected evolution on a global scale using 287 scientists from 160 cities in 26 nations. The study, published in Science, looked at how human activity has impacted the evolution of white clover.

"All of these populations are under selection from the same suite of environmental pressures that we see in cities – things like pavement, pollution, and land-use development," said Andrew Whiteley, a researcher at the University of Sheffield.

They discovered that across gradients from cities to suburbs to rural areas, clover in cities is now more similar to clover in another city a world away than it is to the local variety.

The key point here is that the adaptations to these twin factors are occurring in parallel, thanks to parallel adaptive evolution – when separate populations are affected by the same selective pressure for distinct traits in varied areas. It demonstrates that human modification of the environment has a greater impact on these characteristics than natural occurrences such as local population genetics and climate.

The concept that our species originated in the sub-Saharan savannah and moved into cities to develop a rich culture is called civility.

"We just demonstrated that this happens all the time, and it's often in similar ways on a global scale," added Santangelo of UTM. For evolution to proceed in parallel, cities must converge on environmental factors that impact an organism's fitness, according to the researchers.

Taking a deeper look, the worldwide team discovered that one of the traits changing across city to rural boundaries was hydrogen cyanide production by the plant. This chemical is utilized by white clover as both an anti-predator strategy and as a drought resistance tool.

The villages with the furthest rural populations had 44 percent more chance of manufacturing hydrogen cyanide than those in the cities' center. It appears that grazing is encouraging the production of more hydrogen cyanide in rural areas than urban areas, where grazing pressure isn't as strong; drought becomes the driving force in its place.

Despite the fact that there was significant gene flow between white clover populations along each gradient, this chemical was highly selected for over time.

By expanding the size range of fish in a few years, as we've done with pandas and elephants, it's possible that humans will be able to survive on this planet indefinitely. Humans would have broken the natural size spectrum of animals in the water long ago if not for selective capture by fishermen, leaving more fish with small fish genes to create future generations.

The researchers found that the grazing pressure wasn't as strong in the dry areas, and that drought became the driving force in its place. They also identified a gene that appears to help white clover survive in these tough environments. Despite the fact that there was significant gene flow between white clover populations along each gradient, this chemical was found in higher concentrations in those that grew in dry conditions.

The consequences of our actions are also altering the form of birds. In the UK, the beak size of the common finch has increased by 2.4% over the last 40 years as a result of changes in diet brought about by human activity. These birds now have to work harder to find food, and their beaks have adapted to help them do so.

Zoologist Sarah Otto added, "Cliff swallows' wing spans have evolved to be shorter near roads, with road killed swallow wings lasting longer, suggesting that selection for improved maneuverability in the face of traffic has played a role."

The latest findings provide yet another illustration of a clear urban signal in progress. Evolutionary rates have previously been found to be higher in human communities that are changing versus those that are not.

"This is the most compelling evidence we have that we are influencing the course of life in cities," says UTM biologist Rob Ness. This will be relevant to society beyond ecologists and evolutionary biologists, as predicted human population growth must triple by 2030 in order for us to maintain a healthy environment.

The researchers now have a vast data set they may further examine for human influences on clover evolution. We have a better chance of being able to take the wheel and drive evolution in an informed and safer manner if we understand how we're inadvertently doing it.

As the global human population continues to grow, it is increasingly important for us to better understand how our activities are impacting the natural world.

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About the Blogger:

April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on

To read more of April's blogs, check out her website! She publishes new blogs on a daily basis, including the most helpful mommy advice and baby care tips! Follow on IG @bossbabymav



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