How (and how fast) do new species form?

Why Evolution Is True

Most evolutionists think that speciation, which we see as the origin of a new group whose members are unable to produce fertile hybrids with other such groups (but whose members are interfertile with each other) occurs in the following way. Populations of a single species become geographically isolated by the interposition of geographic barriers like mountains, deserts, water, continental drift, etc. These barriers can either arise de novo, like the Andes, thus isolating populations on either side of them, or result from a rare migration event that is a one-off, like the invasion of the Galápagos by ancestral iguanas, tortoises, or finches. By preventing the mixing of genes among populations of what was initially a single species, the populations can then diverge genetically, often by natural or sexual selection, but also by processes like genetic drift. Different environments, different selective pressures and different mutations will then assure that the geographically isolated populations will…

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