"A new species develops if a population which has become geographically isolated from its parental species acquires during this period of isolation characters which promote or guarantee reproductive isolation when the external barriers break down."

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Species do not grow more perfect: the weaker dominate the strong, again and again- the reason being that they are the great majority, and they are also cleverer. Darwin forgot the mind (-that is English!): the weak possess more mind. ... To acquire mind, one must need mind-one loses it when one no longer needs it.

— Friedrich Nietzsche