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Seeing evolution

It is possible to see evolution in action – often because of human interventions

Evolution is generally a slow process. Selective pressures are often subtle and most genetic mutations do not produce a survival advantage. But there are cases of multicellular organisms evolving rapidly.

Usually these changes are linked to some kind of human activity that has drastically altered selection pressures. Use of pesticides, for example, has led to the emergence of insecticide-resistant mosquitoes.

Deliberate or accidental introduction of new animals into an ecosystem has a big impact. Cane toads, introduced into Australia to control a beetle pest in the 1930s, have spread rapidly through the country. Toads at the front of the invasion, those travelling fastest, have evolved longer legs than those towards the rear. But they’re not the only ones changing.

Cane toads are poisonous, but toad-eating Australian red-bellied black snakes in toad-infested areas have evolved resistance to their toxins (and are also less likely to eat them).

On the US Atlantic coast in the 1800s, mussels faced an influx of European shore crabs brought across by traders. Over time mussels appeared that could detect a chemical released by the crabs and, in response, reinforce their shells.

Then, in 1988, a new invader appeared: an Asian crab, which produces different chemical signals. Mussels from places still free of Asian crabs respond only to signals from the Europeans. But where there are both European and Asian crabs, the mussels reinforce their shells in response to either species – they have undergone a significant evolutionary change in less than 20 years.

More generally, climate change is already having a significant impact on the habitats (and, hence, survival) of organisms and could profoundly shape the evolution of life on Earth. Some organisms may naturally be flexible enough to cope with a changed environment, although signs of adaptation and genetic change have also been identified – the European blackcap, for example, has begun overwintering in the UK rather than Spain.

There are likely to be winners and losers, but – with the rapid pace of change – potentially more losers than winners.

Lead image:

Demietrich Baker/Flickr CC BY


Questions for discussion

  • Does it matter if species go extinct because of human activities?

About this resource

This resource was first published in ‘Evolution’ in January 2007 and reviewed and updated in November 2014.

Cell biology, Ecology and environment, Health, infection and disease
Education levels:
16–19, Continuing professional development