The  Minimum  Genetic  Divergence  Required  for  Speciation  How much
   genetic  separation  is  required  between two populations before they
   become  different species? We shall consider two examples, one from an
   insect  and  the  other  from  a plant, which demonstrate that in some
   cases the answer is "not very much."

   [Page  650]  Researchers  estimate  that Drosophila heteroneura and D.
   silvestris, found only on the island of Hawaii, diverged from a common
   ancestral  species  only  about 300,000 years ago. The two species are
   thought  to  be  descended from D. planitibia colonists from the older
   island  of  Maui (Figure 26-10). The two species are clearly separated
   from  each  other  by  different and incompatible courtship and mating
   behaviors  (a  prezygotic  isolating mechanism), by morphology, and by
   body and wing pigmentation (Figure 26-11).

   Figure 26-10. Proposed pathway for Hawaii's colonization by members of
   the  D.  planitibia species. The purple circle represents a population
   ancestral to the three present-day species.