Almost every side of zoology has contributed to the theory of evolution, but of special importance are the facts and theories associated with the names of Gregor Mendel, A. Weismann and Hugo de Vries. These are discussed under the headings HEREDITY; MENDELISM; and VARIATION AND SELECTION. It has been a feature of great promise in recent contributions to the theory of evolution, that such contributions have received attention almost directly in proportion to the new methods of observation and the new series of facts with which they have come. Those have found little favour who brought to the debate only formal criticisms or amplifications of the Darwinian arguments, or re-marshallings of the Darwinian facts, however ably conducted. The time has not yet come for the attempt to synthesize the results of the many different and often apparently antagonistic groups of workers. The great work that is going on is the simplification of the facts to be explained by grouping them under empirical laws; and the most general statement relating to these that can yet be made is that no single one of these laws has as yet shown signs of taking rank as a _vera causa_ comparable with the Darwinian principle of natural selection.
For evolution in relation to society see SOCIOLOGY.
REFERENCES.--Practically, every botanical and zoological publication of recent date has its bearing on evolution. The following are a few of the more general works: Bateson, _Materials for the Study of Variation_; Bunge, _Vitalismus und Mechanismus_; Cope, _Origin of the Fittest_, _Primary Factors of Organic Evolution_, _Darwin's Life and Letters_; H. de Vries, _Species and Varieties and their Origin by Mutation_; Eimer, _Organic Evolution_; Gulick, "Divergent Evolution through Cumulative Segregation," _Jour. Linn. Soc._ xx.; Haacke, _Schöpfung des Menschen_; Mitchell, "Valuation of Zoological Characters," _Trans. Linn. Soc._ viii. pt. 7; Pearson, _Grammar of Science_; Romanes, _Darwin and after Darwin_; Sedgwick, Presidential Address to Section Zoology, _Brit. Ass. Rep. 1899_; Wallace, _Darwinism_; Weismann, _The Germ-Plasm_. Further references of great value will be found in the works of Bateson and Pearson referred to above, and in the annual volumes of the _Zoological Record_, particularly under the head "General Subject." (P. C. M.)