"A group of interbreeding natural populations that are reproductively isolated from other such groups."By "reproductively isolated," we mean that individuals in two different species do not generally produce viable offspring. Coyne points out that there's no obvious reason that life should be divided into discrete species—instead it could have all blurred together, so that every point between, say, "cat" and "dog" was equally represented. While "God did it" would be equally compatible with these or any set of circumstances, evolution explains our specific observations perfectly.
"After all, there's no obvious reason why a creator would produce similar species of birds or lizards on continents but not on isolated islands."Third, we should be able to observe reproductive barriers forming and speciation occurring in the wild, albeit very slowly. The example Coyne gives is the orchid Satyrium hallackii, which for now is classified as one species. In northern South Africa they have long nectar tubes that allow only hawkmoths and long-tongued flies to pollinate them, while they have short nectar tubes on the coast, where bees are the only available pollinators. The two groups are genetically isolated, and would probably remain so even if they lived in the same area.
Satyrium carneum, a close relative of the orchid Coyne mentions |
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