Chapter IV Evolution as the Key to Distribution
Importance of the Doctrine of Evolution—The Origin of New Species—Variation in Animals—The amount of Variation in North American Birds—How New Species Arise from a Variable Species—Definition and Origin of Genera—Cause of the Extinction of Species—The Rise and Decay of Species and Genera—Discontinuous Specific Areas, why Rare—Discontinuity of the Area of Parus Palustris—Discontinuity of Emberiza Schœniclus—The European and Japanese Jays—Supposed examples of Discontinuity among North American Birds—Distribution and Antiquity of Families—Discontinuity a Proof of Antiquity—Concluding remarks
Pages 55-71