Survival adaptations: how living things fit their environment

What an adaptation is

• An adaptation is a feature of a living thing that helps it survive and reproduce in its environment.
• Every organism needs to get resources (food, water, light, shelter), avoid hazards (predators, cold, drought) and reproduce.
• Adaptations are inherited: they are passed from parents to young, not learned or grown during one lifetime.
• An organism's adaptations suit the place it lives. A feature that is useful in one habitat may be useless, or even a problem, in another.

Three kinds of adaptation

• Structural adaptations are physical features of the body: its shape, size, colour or covering.
• Behavioural adaptations are things an organism does: the way it acts.
• Physiological adaptations are processes inside the body: chemistry you cannot see from the outside.

Try it: what kind of adaptation?

Getting resources, avoiding danger, reproducing

• Getting resources: plant roots spread wide or deep to reach water, and leaves turn towards light.
• Avoiding hazards: stick insects look like twigs (camouflage), ongaonga (tree nettle) is covered in stinging hairs, and many animals freeze or flee when a predator is near.
• Reproducing: male kākāpō make deep booming calls to attract females, kererū swallow large fruit and spread the seeds of trees such as taraire and tawa, and a kiwi father sits on the egg until it hatches.

Suited to a place

• Ducks such as pāteke (brown teal) have webbed feet that push against water like paddles, so they swim well. On land they waddle.
• Kiwi lost the ability to fly while living in forests with no ground-hunting mammals. Running, burrowing and a strong sense of smell suited that world.
• When people brought stoats, cats and dogs to New Zealand, that same ground-living life became a weakness, and kiwi numbers fell sharply.
• So an adaptation is only good or bad compared with a particular environment.

No two individuals are the same

• Members of the same species are not identical. They differ in size, colour, speed, thickness of fur and many other traits. This is called variation.
• Much of this variation is inherited from parents.
• In a particular environment, some variations work better than others. A slightly darker snail may be harder for a bird to spot on dark soil.
• Individuals with better-suited traits tend to survive longer and have more young, and those young can inherit the useful trait.

Camouflage depends on the background

• Peppered moths in England come in pale and dark forms. They rest on tree trunks by day, where birds hunt them.
• On pale, lichen-covered bark the pale moths were hard to see, and the dark moths were eaten more often.
• In the 1800s, factory soot blackened the trees around industrial cities. There, the dark moths were hidden and became common, while the pale ones were picked off.
• When the air was cleaned up, the bark lightened again and the pale form became common once more. The same colour helped in one place and harmed in another.

Try it: toothpicks left on the lawn

Better odds, not a guarantee

• An adaptation raises the chance that an individual survives and reproduces. It cannot make survival certain.
• Even well-camouflaged moths were sometimes eaten, and some badly hidden ones lived; the difference showed up across many moths.
• A storm, a disease or a new predator can kill well-adapted individuals too.
• What matters over generations is that, on average, better-suited individuals leave more young.

Lamarck's idea, and why it failed

• In the early 1800s the French naturalist Jean-Baptiste Lamarck suggested that features an animal gains during its life are passed to its young.
• His famous example: giraffes stretched their necks to reach high leaves, their necks grew a little longer, and their calves were born with longer necks.
• Evidence did not support this. A weightlifter's big muscles are not passed to their children, and in the 1880s August Weismann cut the tails off mice for several generations, yet every new generation was born with normal tails.
• Scientists now explain adaptation by variation and inheritance instead: giraffes that happened to be born with longer necks reached more food, survived better and passed on that trait.