RAPID EVOLUTION IN ACTION

We think of evolution as a slow, gradual process, but that’s not always the case. Some species undergo a rapid transformation

- ALEX DALE

INSECT

MOTHS THAT GOT DARKER, THEN LIGHTER

The most famous example of ‘microevolution’ – evolution that occurs within 100 years and can be observed in a human lifetime – is a phenomenon we call ‘industrial melanism’. This most commonly occurs in butterflies and moths, and the most studied case is that of the peppered moth in Great Britain. Before the Industrial Revolution, the vast majority of peppered moths were white with a speckled pattern on their wings – only a small proportion of the species’ population boasted black bodies and wings. Natural selection favoured the white moths because their speckled colours allowed them to blend in with the lichen on tree bark, camouflaging them from predators.

However, in urban areas, smoke from factories changed the moths’ environment, both by killing off much of the lichen and darkening the tree bark itself. This increased the black moths’ chances of surviving to pass on their genes over the years, leading to an ever-darkening population of peppered moths. Now that the air is cleaner, the speckled form is more common once again.

PLANT

THE SEEDS THAT GOT HEAVIER