The biological species concept

The biological species concept is the most widely accepted species concept. It defines species in terms of interbreeding. For instance, Ernst Mayr (opposite, on the right) defined a species as follows:

"species are groups of interbreeding natural populations that are reproductively isolated from other such groups."

The biological species concept explains why the members of a species resemble one another, i.e. form phenetic clusters, and differ from other species.

When two organisms breed within a species, their genes pass into their combined offspring. As this process is repeated, the genes of different organisms are constantly shuffled around the species gene pool. The shared gene pool gives the species its identity. By contrast, genes are not (by definition) transferred to other species, and different species therefore take on a different appearance.

For many biologists, the biological species concept is the most appropriate definition of a species. Richard Dawkins gives his opinion on this issue.