Humans a dominant force driving plant evolution, Canadian study finds

A global collaboration led by University of Toronto Mississauga evolutionary biologists examined more than 110,000 white clover samples from 160 locations across the world. (Photo courtesy Nick Iwanyshyn)

A new study conducted by biologists out of the University of Toronto Mississauga (UTM) suggests that urban environments are altering the way plant life evolves.

The study, published Thursday in peer-reviewed journal Science, reports that humans are constantly re-shaping the environment by building cities, which changes the way life evolves.

According to the study, the Global Urban Evolution Project analyzed white clover plant data collected by 287 scientists in 160 cities, and their surrounding rural area, across 26 countries, including in Toronto, Tokyo, Melbourne and Munich.

The scientists say they found the "clearest evidence yet" that humans in general, and more specifically the cities they build, are a "dominant force" driving the evolution of life across the world. Scientists say this because the data showed white clover frequently evolving in direct response to environmental changes taking place in urban settings.

"We've long known that we've changed cities in pretty profound ways and we've dramatically altered the environment and ecosystems," said UTM biology PhD student and study co-lead James Santangelo in a press release. "But we just showed this happens, often in similar ways, on a global scale."

According to the study, the environmental conditions in cities were found to be more similar to each other than to the nearby rural habitats. For example, scientists reported that downtown Toronto was found to be more comparable to downtown Tokyo, rather than the surrounding farmland and forests outside of the city.

In addition to observing global adaptation to cities, the scientists say they were able to identify the genetic basis of that adaptation, as well as the environmental drivers of evolution.

White clover, a low-growing perennial commonly found in lawns, produces hydrogen cyanide both as a defence mechanism against herbivores and to increase its tolerance to water stress. Scientists chose to examine this plant because it is one of the few organisms present in almost every city on Earth.

According to the study, white clover growing in cities typically produces less hydrogen cyanide than those in neighbouring rural areas due to "repeated adaptation to urban environments."

Scientists say the changes in the number of herbivores and presence of water stress in cities is pushing white clover to adapt differently than the plants in rural regions. The study states this finding held true for cities across a variety of climates, which they say could mean implications for other plants and even humans.

"This study is a model to understand how humans change the evolution of life around us," said UTM assistant biology professor Rob Ness in the release. "Cities are where people live and this is the most compelling evidence we have that we are altering the evolution of life in them."

"Beyond ecologists and evolutionary biologists, this is going to be important for society," he added.

With the study showing humans as the driving force of evolution in cities, scientists say the data can be used to develop strategies to better conserve rare species and help them adapt to urban environments.

Scientists note the findings can also aid in how to prevent unwanted pests and diseases from adapting to human environments.

However, the authors say this study is just the beginning.

By collecting more than 110,000 clover samples from cities and their nearby rural areas across the world, scientists have sequenced more than 2,500 clover genomes, creating a "massive dataset" that can be studied for years to come.