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 Schoeniclus--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

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