Post-Darwinian books on evolution fall naturally into four classes. I. Those which preach Wallaceism, as, for example, Wallace’s Darwinism , Poulton’s Essays on Evolution , and the voluminous works of Weismann. II. Those advocating Lamarckism. Cope’s Factors of Evolution and the writings of Haeckel belong to this class. III. The writings of De Vries, forming a group by themselves. They advocate the theory that species spring suddenly into being; that new species arise by mutations from pre-exist

Pre-Darwinian Evolutionists—​Causes which led to the speedy triumph of the theory of Natural Selection—​Nature of the opposition which Darwin had to overcome—​Post-Darwinian biology—​Usually accepted classification of present-day biologists as Neo-Lamarckians and Neo-Darwinians is faulty—​Biologists fall into three classes rather than two—​Neo-Lamarckism: its defects—​Wallaceism: its defects—​Neo-Darwinism distinguished from Neo-Lamarckism and Wallaceism—​Neo-Darwinism realises the strength and

Brief statement of Theory—​Objections to the Theory fall into two classes—​Those which strike at the root of the Theory—​Those which deny the all-sufficiency of Natural Selection—​Objections which strike at root of Theory are based on misconception—​Objections to Wallaceism—​The Theory fails to explain the origin of Variations—​Natural Selection called on to explain too much—​Unable to explain beginnings of new organs—​The Theory of change of function—​The co-ordination of variations—​The fertil

The assumption of Darwin and Wallace that variations are haphazard in origin and indefinite in direction—​If these assumptions be not correct Natural Selection ceases to be the fundamental factor in evolution—​Darwin’s views regarding variation underwent modification—​He eventually recognised the distinction between definite and indefinite variations, and between continuous and discontinuous variations—​Darwin attached but little importance to either definite or discontinuous variations—​Darwin’

The alleged sterility of hybrids a stumbling-block to evolutionists—​Huxley’s views—​Wallace on the sterility of hybrids—​Darwin on the same—​Wallace’s theory that the infertility of hybrids has been caused by Natural Selection so as to prevent the evils of intercrossing—​Crosses between distinct species not necessarily infertile—​Fertile crosses between species of plants—​Sterile plant hybrids—​Fertile mammalian hybrids—​Fertile bird hybrids—​Fertile hybrids among amphibia—​Limits of hybridisat

Phenomena which a complete theory of inheritance must explain—​In the present state of our knowledge it is not possible to formulate a complete theory of inheritance—​Different kinds of inheritance—​Mendel’s experiments and theory—​The value and importance of Mendelism has been exaggerated—​Dominance sometimes imperfect—​Behaviour of the nucleus of the sexual cell—​Chromosomes—​Experiments of Delage and Loeb—​Those of Cuénot on mice and Castle on guinea pigs—​Suggested modification of the genera

The theory of protective colouration has been carried to absurd lengths—​It will not bear close scrutiny—​Cryptic colouring—​Sematic colours—​Pseudo-sematic colours—​Batesian and Müllerian mimicry—​Conditions necessary for mimicry—​Examples—​Recognition markings—​The theory of obliterative colouration—​Criticism of the theory—​Objections to the theory of cryptic colouring—​Whiteness of the Arctic fauna is exaggerated—​Illustrative tables—​Pelagic organisms—​Objectors to the Neo-Darwinian theorie

Meaning of the term—​Fatal to Wallaceism—​Sexual Selection—​The law of battle—​Female preference—​Mutual Selection—​Finn’s experiments—​Objections to the theory of Sexual Selection—​Wallace’s explanation of sexual dimorphism stated and shown to be unsatisfactory—​The explanation of Thomson and Geddes shown to be inadequate—​Stolzmann’s theory stated and criticised—​Neo-Lamarckian explanation of sexual dimorphism stated and criticised—​Some features of sexual dimorphism—​Dissimilarity of the sexe

Variation along definite lines and Natural Selection are undoubtedly important factors of evolution—​Whether or not sexual selection is a factor we are not yet in a position to decide—​ Modus operandi of Natural Selection—​Correlation an important factor—​Examples of correlation—​Correlation is a subject that requires close study—​Isolation a factor in evolution—​Discriminate isolation—​Indiscriminate isolation—​Is the latter a factor?—​Romanes’ views—​Criticism of these—​Indiscriminate isolatio