six sets of chromosomes, two sets from each of three different specices
a region in which members of different species meet and mate, producing at least some offspring of mixed ancestry
a process in which natural selection strengthens prezygotic barriers to reproduction, thus reducing chances of hyrbid formation. Such a process is likely to occur only if hybrid offspring are less fit than members of the parent species
In a __, new species change most as they branch from a parent species and then change little for the rest of their existence.
In the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change.