There are millions of kinds, or species, of living thing. Each species is unique. For example the European hedgehog's back is covered with a thick coat of brown spines with pale yellow tips. It also has short ears. There are several other species of hedgehogs around the world, but none of them has exactly the same features as the European hedgehog. For example the desert hedgehog has spines which are banded with dark brown and it has long ears. Differences like these allow you to tell one species from another.

The males and females in the same species are capable of breeding together and producing offspring which can also breed. The males and females of different species do not produce breeding young. For example if a male donkey and a female horse are allowed to breed they produce a mule. However, the mule is not capable of breeding. The mule is not a species - it is called a hybrid. There are many hybrid plants in garden centres today. These are crosses between different species, too.