Species

Members of a species are not all identical. They may inherit different versions of genes, called alleles, and so have different characteristics, or phenotypes. Mutations produce new genetic variants, although most mutations have no effect on phenotype.

Individuals belonging to the same species are not usually genetically identical. A population therefore normally contains extensive genetic variation: there are many differences in DNA among its members.

The rabbit belongs to a species. All the rabbits living in that meadow at the same time form a population. A population contains members of just one species; the foxes in the meadow form a separate population.

An individual belongs to a species. Members of the same species can reproduce with one another to produce fertile offspring. Naming the species matters when moving to the next level because a population includes only one species.