Adaptation: how populations change

An adaptation is a feature that helps a living thing survive and reproduce where it lives. The kiwi's long bill, with nostrils at the tip, sniffs out worms underground. The tūī's brush-tipped tongue mops up nectar. But where do adaptations come from?

Three ingredients

Put the three together and the individuals with helpful features leave more offspring. Their features become more common in the next generation, and the next. Over many generations the population changes. That is evolution by natural selection, the idea worked out by Charles Darwin and Alfred Wallace.

A tree that remembers the moa

Young horoeka (lancewood) have long, stiff, narrow leaves with sharp teeth, pointing down like a bundle of spears. Once the tree grows taller than about 3 metres, it grows short, soft, ordinary leaves. One strong idea is that the spiky young form protected horoeka from browsing moa, which could reach about that high. Moa died out centuries ago, but the trees still carry the feature, because evolution is slow.

When the pressure changes fast

In England, a dark form of the peppered moth became common when soot blackened the trees, then rare again when the air was cleaned. In Aotearoa, birds evolved for millions of years without ground predators, so flightlessness and nesting on the ground were safe. When people brought rats, stoats and cats, those features became deadly almost overnight. The change came far faster than a population can adapt.

One animal can't adapt

A single animal can't grow a new feature because it needs one. Populations change, and only over generations. When you ask which species at your site are winning or losing, ask which features help them now, and whether the change is happening too fast for them.