The differences between living things of the same species are called variation. Variation between species is always greater than variation within a species. Within any population of living organisms there will be inherited variations. Within each species the individuals with the variation best suited to the environment will survive better than the others; these survivors have a higher chance of reproducing. When they do reproduce, they pass on the genetic information for their variations to their offspring. Over time this is how species evolve. This process is what is known as natural selection. Over time a population can change so much it may even become a different species, unable to reproduce sexually with individuals of the original species.
By the end of this topic, children will be able to recognise that living things have changed over time and that fossils provide information about living things that inhabited the Earth millions of years ago. They will also be able to recognise that living things produce offspring of the same kind, but normally offspring vary and are not identical to their parents. They will identify how animals and plants are adapted to suit their environment in different ways and that adaptation may lead to evolution.