Evolution__3rd_Edition

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14Speciation
S peciation means the evolution of reproductive isolation
between two populations. Two main processes have been
suggested by which reproductive isolation can evolve.
Reproductive isolation may evolve as a by-product of
evolutionary divergence between two populations. Or it
may be directly favored, in a process called reinforcement.
This chapter begins by showing that we have extensive
evidence for, and a good theoretical understanding of, the
“by-product” theory of speciation. The evidence comes from
laboratory experiments and biogeographic observation. The
chapter then goes on to look at the theory of reinforcement.
This theory is controversial: the evidence is inconclusive and
we cannot show either that it is important or that it is trivial.
The chapter also looks at the special case of hybrid speciation
in plants, at the possibility of speciation between populations
that are not geographically separated, and at two current
research trends a the influence of sexual selection on
speciation, and the use of modern genomic techniques
to identify genes that cause reproductive isolation.