How does one species become two species? Species appear to be stable, adapted entities reproductively isolated from related species, but how did this isolation appear? We can view species in terms of populations in an adaptive landscape—a topographical plot of fitness as a function of combinations of characteristics, Each species then sits on its own high ground, sporting adaptive characteristics (collectively, their phenotypes), while they tower over valleys of maladaptive phenotypes. Does this high ground represent isolated peaks, each species inhabiting one of them, or are the areas of high ground connected by an equally high ridge, long and circuitous though it may be?
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