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Evolution in Action
What is a species? Although gross morphological, physical, behavioral, and physical characters are most often used to describe and illustrate a species, it is reproduction that is the ultimate factor in defining a species.

A species is any genetically distinct group or population that shares a common gene pool and is reproductively isolated from other similar groups or populations.

Gene flow can take place only within a species, not across species boundaries. If no gene flow is possible between two groups, then they are different species, no matter how alike they look.

© 2001, Professor John Blamire