In 1903, Weismann’s theory of the continuity of the germplasm was ten years old.  De Vries’ experiments in variation and Mendel’s rediscovered work on plant hybridization had hopelessly undermined the older notion that the evolution or progress of species has taken place through the inheritance of acquired characters—­that is, that the individuals developed or adapted themselves to suit their surroundings and that these body-modifications were inherited by their offspring.  As pointed out in Chapter I, biologists have accepted Weismann’s theory of a continuous germplasm, and that this germplasm, not the body, is the carrier of inheritance.  Nobody has so far produced evidence of any trace of any biological mechanism whereby development of part of the body—­say the biceps of the brain—­of the individual could possibly produce such a specific modification of the germplasm he carries as to result in the inheritance of a similar development by his offspring.

Mendel’s experiments had shown that the characters we inherit are units or combinations of units, very difficult to permanently change or modify.  They combine with each other in all sorts of complicated ways.  Sometimes one will “dominate” another, causing it to disappear for a generation or more; but it is not broken up.  These characters have a remarkable way of becoming “segregated” once more—­that is, of appearing intact later on.

While it follows from Weismann’s theory that an adaptation acquired by an individual during his lifetime cannot be transmitted to his offspring, it remained for De Vries to show authoritatively that evolution can, and does, take place without this.  Once this was established, biologists cheerfully abandoned the earlier notion.  Lester Ward and the biologists of his day in general not only believed in the transmission of acquired characters, but they filled the obvious gaps which occurred in trying to apply this theory to the observed facts by placing a fantastic emphasis upon sexual selection.  That is, much progress was accounted for through the selection by the females of the superior males.  This, as a prime factor in evolution, has since been almost “wholly discredited” (Kellogg’s phrase) by the careful experiments of Mayer, Soule, Douglass, Duerigen, Morgan and others.  The belief in sexual selection involved a long string of corollaries, of which biology has about purged itself, but they hang on tenaciously in sociological and popular literature.  For instance, Ward believed in the tendency of opposites to mate (tall men with short women, blonds with brunettes, etc.), although Karl Pearson had published a statistical refutation in his Grammar of Science, which had run through two editions when the Pure Sociology appeared.  The greater variability of males than females, another gynaecocentric dogma had also been attacked by Pearson on statistical evidence in 1897 (in the well-known essay on Variation in Man and Woman, in Chances of Death) and has become increasingly unacceptable through the researches of Mrs. Hollingworth[6,7,8].  The idea of a vanished age of mother-rule in human society, so essential to the complete theory, has long since been modified by anthropologists.