CHILDREN resemble their parents, and the characters of the species are transmitted from generation to generation. Darwin in 1859 stated that heredity must be subject to natural laws at that time as yet unknown. He noted that if individuals, of different races be crossed, their descendants will exhibit combined and intermediate characters which in the course of succeeding generations tend to revert to their original forms, that is, revert to type.
It is common knowledge indeed that cross-breeding gives rise to offspring exhibiting characters from the male line in combination with others from the female. The distribution of these characters from different sources is not constant in all cases, though the offspring will always exhibit morphological and functional elements, which have descended to it from its two parent strains. Sometimes the influence of one parent will predominate greatly over the other, giving what we call alternating heredity, whilst in others and indeed the greater number of cases the form of the child is intermediate or halfway between that of the two parents, either in mosaic where the interpolation of the paternal and maternal characters is visible, or in blending or fusion. Naudin in 1863 crossed individuals of different races and even of different species and showed that offspring of the first generation were usually intermediate between their two progenitors, bearing greater resemblance to the male parent in some cases and to the female in others, though in general there seemed to be a balanced distribution of characters. Naudin also pointed out a reversion to original type of one of the parental lines releasing the offspring from the influence of the least dominant progenitor after a series of generations.
Francis Galton, who in fact was a cousin of Darwin, studied the phenomena of heredity from the statistical angle in accordance with methods which had been proposed by Quetelet in 1845. In 1889, Galton was in a position to formulate the quantitative laws of heredity,