Note 815 — Chapter XIII · —Island Peoples

Despite this general poverty of species, island life is distinguished by a great proportion of peculiar or endemic forms, and a tendency toward divergence, which is the effect of isolation and which becomes marked in proportion to the duration and effectiveness of isolation. Isolation, by reducing or preventing the intercrossing which holds the individual true to the normal type of the species, tends to produce divergences.815 Hence island life is more or less differentiated from that of the nearest mainland, according to the degree of isolation. Continental islands, lying near the coast, possess generally a flora and fauna to a large extent identical with that of the mainland, and show few endemic species and genera; whereas remote oceanic islands, which isolation has claimed for its own, are marked by intense specialization and a high percentage of species and even genera found nowhere else.816 Even a narrow belt of dividing sea suffices to loosen the bonds of kinship. Recent as are the British Isles and near the Continent, they show some biological diversity from the mainland and from each other.817