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