CHAPTER II.

SPECIAL PROOFS OF EVOLUTION.

_Introductory._

_Special proofs necessary_--Evolution, though certain, is not yet accepted by the popular mind--Different departments from which proofs are drawn 67

_Origin of new organic forms; the old view briefly stated_-- Necessary to give a brief statement of theories--Old view-- Permanency of specific types--Supernatural origin of species --Centers of creation--Explanation of facts of geographical distribution--Of geological distribution--Modification of extreme view--Variability, but within limits--Illustrated 68

_The new view briefly stated_--Indefinite variability of organic forms--Effect of environment on rigid forms--On plastic forms--Taxonomic groups represent degrees of kinship 72

_Factors of evolution_--(1) Physical environment--(2) Use and disuse of organs--(3) Natural selection--(4) Sexual selection--(5) Physiological selection--Its necessity shown --Its operation explained--Compared with natural selection --Cause of variation unknown--Explanation of this is the next great step in the theory of evolution 73