What constitutes a species?

Identifying different species has become increasing complicated.

9th April 2010
What constitutes a species? (iStock)

Asked by: Anonymous

Species are a naming convenience applied by biologists as they try to group similar animals together. Ernst Mayer defined a species as a group of actually or potentially interbreeding natural populations and this is a working definition that many biologists use.

But there are at least a dozen other ways to categorise species, involving evolutionary history, morphology or DNA analysis. The problem is that evolution doesn’t act on species directly. Natural selection applies at the level of the gene, the individual or the breeding population. Species are just a pattern that appears as a result.

We can easily identify species from a distance, but examine them closely, and the edges blur. The standard definitions of species really break down when you consider single-celled, asexual organisms.


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