Evolution and Extinction

Throughout these pages we look at changes in plants and animals. These changes produced the many and varied species that are alive today, and thousands that are now extinct.

All the changes took millions of years. No animal or plant can deliberately alter its body to enable it to survive in new conditions. The changes took place as a result of what is called evolution, a process that is still going on today.

The human race, like every other species on earth,
underwent a process of evolution.

The 'struggle for existence'

Life is always changing because the world around us is altering too. There is the additional fact that many more plants and animals are born than there is food or room for. A single cod may lay 4 million eggs in a year. If every egg hatched, then the oceans would quickly be a seething mass of cod, assuming they could find enough food to eat and room to grow. So there is all the time what the famous nineteenth-century scientist Charles Darwin called a 'struggle for existence' between living things, and many of them die.

Natural selection

Even within the same species there are differences between individuals. Some of these different forms do better in the struggle for existence than others. The unfit are killed off and the fittest survive. This means that in the next generation there will be more offspring of the fittest than of the unfit. This 'weeding out' of the unfit, leaving the fittest, is called 'natural selection'. Since young animals and plants, on the whole, resemble their parents, the population becomes a little more like the fittest animals or plants with each generation that passes. And in the course of perhaps millions of years, the original species may change to a quite different one.

Different kinds of 'fitness'

There are many different forms of 'fitness'. Fleetness of foot, ability to swim, strength of muscles, sharpness of teeth, warmth of fur, resistance to disease, camouflage-colouring or some other protection from enemies, ability to win a mate - any of these and many more may help an animal to survive. It must also be remembered that what is an advantage in some conditions may be a disadvantage in others. For example, in most places insects with wings are the fittest, for they can fly about and readily seek new sources of food. But on a small windy island, winged insects would get blown out to sea, so there the wingless insects are more fit to survive.

As well as changes in the climate or the form of the Earth's surface, there are other changes that can affect animals. If the plants gradually change, for example by developing thorns or chemical substances to protect them, then the animals that eat those plants must also change their way of feeding. Changes in food animals will affect their predators. Species that cannot change to meet the new conditions become extinct.

The elephant's trunk is an elongated nose. It is used
for smelling, gathering food, drinking and fighting.
The tusks are modified teeth.