Biological species concepts

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Species

Smallest independently evolving unit

Independent evolution occurs when mutation, selection, gene flow, and drift operate independently in different populations

Therefore, these species will follow independent evolutionary trajectories

Potentially 23 different species concepts

Biological Species Concept (BSC)

"Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups."

The Biological Species Concept is the first modern attempt to define species, but numerous problems with this concept, on both theoretical and practical grounds

Prezygotic Isolating Mechanisms

Prezygotic Isolating Mechanisms prevent the formation of zygotes.
Ecological Isolation

Even if two species occur in the same area, they may utilize different portions of the environment and thus do not hybridize because they do not encounter each other.
Lions and Tigers in India