3.1.6—Speciation

Speciation becomes possible when isolation reduces gene flow and divergence eventually prevents production of fertile offspring.

Geographic, ecological or behavioural separation lets mutation, selection and chance accumulate differences. Under the biological species model, reproductive isolation is the decisive test.

A river separates populations; if they later meet but cannot produce fertile offspring, the sequence supports completed speciation.

No. It reduces gene flow, but reproductive isolation must be demonstrated or inferred carefully.

Divergence and speciation are not identical; ask whether gene flow and fertile reproduction remain.