Extreme evolution: The animals evolving at super speed to survive

Humans have become one of the world's greatest evolutionary forces. To survive our cities, animals from urban foxes to glass-climbing lizards are responding with extreme adaptation.

In Puerto Rico, the anole lizards living in cities look rather different to their forest-dwelling counterparts. In order to scale buildings and sprint across hot surfaces, these urban reptiles appear to have evolved longer limbs and more toe lamellae – the fine scales on the bottom of their feet. These traits are believed to help them better cling to smooth human-made surfaces like glass and metal. And the change seems to have happened in a matter of years. 

Cities have become the planet's newest ecosystem, and many of the animals residing in them have been forced to adapt to survive.

At the extremes, these changes – either behavioural or genetic – happen over very short timeframes, sometimes just a few generations. These speedy changes are happening either to cope with climate change, or direct human activity. Human choices and behaviour, from the use of antibiotics to the transfer of invasive species, have become one of the world's greatest evolutionary forces, driving wildlife species to dramatically accelerate their pace of change. It's known as "contemporary evolution".

"Some animals in cities are responding well," says Andrew Sih, who studies the evolution of animal behaviour at University of California at Davis. 

That response can encompass a range of profound changes – from recognising novel predators, finding new ways to get food or shelter, adjusting to the noise and excess light, and avoiding toxins and pathogens.

One study found that animals able to adapt to urban settings sometimes benefit from an more food availability and fewer predators – which can lead to more offspring. This means cities – at first glance an unfriendly environment for wildlife – can actually lead some species to flourish.

British red foxes are a well-documented example of how urban populations often have higher reproductive rates than their rural counterparts due to food availability in the cities. In the US, city-dwelling raccoons – fondly nicknamed "trash pandas" – are physically changing. A recent study found urban raccoons are showing early signs of domestication, developing snorter snouts and becoming less aggressive around humans.

Meanwhile in Denmark, the urban hare has been seen making tentative forays into city life. The animal has adapted to human presence by increasing its tolerance towards human disturbance. This could either be due to a change in how it expresses its genes, or a Darwinian selection process of more tolerant individuals.

Research published in 2025 found animals from urban areas, exposed to higher temperatures and greater pollution, demonstrated "significantly higher" resilience to stressful........

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