What makes a species
? Members of the same species have a similar
, at least when compared to members of a different species.
They presumably share a common ancestry, and are more closely related to conspecific
than to members of a different species. Biologist
s have used a variety of ways of
thinking about the concept of "species", including these criteria; the
conceptualization in the evolutionary biology
is called the Biological Species Concept.
One of the first to articulate the Biological Species Concept was Ernst Mayr in 1940, who
defined a species as
"groups of actually or potentially interbreeding natural populations which are
reproductively isolated from other such groups."
Here are the main points of the Biological Species Concept:
- Populations. A species is made up of populations, not of individuals.
- Interbreeding. Populations that are part of the same species interbreed, or at least
could if they were in spatial proximity. A species represents a single gene pool.
- Reproductive isolation. Mechanisms exist that prevent gene exchange between
populations of different species that coexist.
The Biological Species Concept overcomes problems that arise with a purely morphological
definition of species -- sexual dimorphism
, and simple variation within a
population can result in conspecifics with large differences in morphology. However,
with its emphasis on interbreeding
as a mechanism for gene
exchange, the Biological
Species Concept doesn't work well with types of organism
s that do not reproduce sexually