De Vries’ experiments showed that a moderately simple fact practically makes all these complicated theories unnecessary.  No two living things are exactly alike—­that is, all living matter is more or less variable.  Some variations are more fortunate than others, and these variants are the ones which survive—­the ones best adapted to their environment.  Given this fact of the constant variation of living matter, natural selection (i.e., survival of the fittest and elimination of the unfit) is the mechanism of evolution or progress which best accounts for the observed facts.  Such variation is called “chance variation,” not because it takes place by “chance” in the properly accepted sense of the term, but because it is so tremendously varied—­is evidently due to such complicated and little-understood circumstances—­that it can best be studied mathematically, using statistical applications of the “theory of probabilities.”

The fine-spun, elaborate theories about sex, so current twenty years ago, have fallen into almost complete desuetude among scientists.  With the discovery of the place of the chromosomes in inheritance, biologists began to give their almost undivided attention to a rigid laboratory examination of the cell.  This has included sex phenomena since McClung and Sutton pointed out the function of the sex chromosome in 1902 and 1903.  Present-day “theories” are little more than working hypotheses, developed, not in a library or study, but with one eye glued to a high-power microscope.

Besides its faulty foundation as to facts, the old gynaecocentric theory involved a method of treatment by historical analogy which biologists have almost entirely discarded.  Anyone interested in the relative value of different kinds of biological data for social problems would do well to read the opening chapter of Prof.  Morgan’s “Critique of the Theory of Evolution"[9], for even a summary of which space is lacking here.  College reference shelves are still stocked with books on sex sociology which are totally oblivious of present-day biology.  For example, Mrs Gilman (Man-Made World), Mrs Hartley (Truth About Woman) and the Nearings (Woman and Social Progress) adhere to Ward’s theory in substantially its primitive form, and not even sociologists like Professor Thomas (Sex and Society) have been able to entirely break away from it.

The old question of male and female predominance in inheritance has been to a considerable extent cleared up, to the discomfiture of both sides to the controversy.  Most exhaustive experiments failed to trace any characters to any other part of either sperm or egg than the nucleus.  Transmission of characteristics seemed to be absolutely equal by the two parents.  The male nucleus enters the egg practically naked.  Hence if the characters are transmitted equally, there is certainly ground for supposing that only the nucleus of the egg has such functions, and that the remainder merely provides material for early development.  Yet this does not seem to be strictly true.