We often think of humans as having a solely negative impact on the natural world. But the development and spread of urban areas is having another impact on wildlife. We have effectively created a new ecosystem, with new niches and opportunities for organisms to exploit, and new pressures to influence them.

A new paper has found that urbanization is driving the rapid evolution of many species, changing their appearance, size, and migratory behavior. The study, published in the Proceedings of the National Academy of Science, looked at over 1,600 species of both plants and animals, and found a “clear sign” of this impact that cities and urban spaces are having on the wildlife that now calls them home.

“We found a clear urban signal of phenotypic change – and greater phenotypic change in urbanizing systems compared to natural and non-urban anthropogenic, or human-created systems,” explained the paper’s lead author, Marina Alberti, from the University of Washington. “By explicitly linking urban development to heritable traits that affect ecosystem function, we can begin to map the implications of human-induced trait changes for ecological and human well-being.”

The shifts in how organisms function in the increasingly urban environment could have profound impacts on the ecosystems developing in cities. For example, these changes could alter biodiversity, which in turn could change nutrient cycling, water purification, and even food production, or how diseases emerge and spread. Birds have already been found to be shifting their migratory patterns, and with recent outbreaks of the H5N1 virus across much of Europe, it could have important consequences on its dispersal.

But while we are clearly having an impact on the wildlife that manages to move into and survive in our cities and urban areas, it is not necessarily a bad thing. “Certainly many species have been, and will continue to be, extinguished by human action,” said co-author John Marzluff. “But we reveal how others are evolving the necessary strategies and physical characteristics to coexist with humanity.”

It used to be thought, and was even stated by the “father” of evolutionary theory himself, Charles Darwin, that evolution happened at such a glacial pace that we can only see it occurring over massive time scales, and preserved in the fossil record for us to decode. But we now know that is no longer the case.

“We have a completely different view,” write the authors in a separate review paper published in the Philosophical Transactions of the Royal Society B. “Rapid evolution is occurring all around us all the time. Many of the most extreme examples of rapid evolution are associated with human influences, leading to the oft-repeated assertion that humans are ‘the world’s greatest evolutionary force.’”