But the method whereby this is achieved has remained a mystery.
Professor Punnett says with regard to the phenomenon:
"The mother transmits to her daughter the dominant faculty of femaleness, but to balance this, as it were, she transmits to her sons another quality which her daughters do not receive ... among human families, in respect to particular qualities, the sons tend to resemble their mothers more than their daughters do."
A striking illustration of such transmission by mother to son of a paternally-derived abnormal inherence which she herself does not develop, is found in so-called "bleeders"; persons who suffer from the disease, hæmophilia. The daughters of a "bleeder" father show no symptom at all of the affliction, but they, nevertheless, pass on to their sons this male heritage of the grandfather.
There are numerous other examples of traits and diseases thus "skipping a generation"—in other words, of lying dormant, or potential, merely; overshadowed in the constitution and psychology of the sex to which they do not rightly belong, but developing in a succeeding generation in offspring of that sex whereof they are a natural trait, or (so to speak) a natural defect.
Since the woman-half she contributes to their hybrid constitution engenders the potential of their living processes, the mother may be regarded as still mothering her children throughout development and maturity, and to the end of their natural term. Accounting for that mystical sympathy between mother and child which intuitively informs her of fatalities occurring to absent sons and daughters—but to sons pre-eminently. Marvellously, they remain one living flesh so long as life persists.
During the War, mothers at a distance have known by an intuitive flash, and have told of the death of sons cut down in battle. One mother described the sensation she experienced as being precisely as though one side of her body had been suddenly torn away. So too, mothers whose infants have died during childbirth or shortly after, describe as persisting for months subsequently a sense as though part of them were dead.
The father too must function in the hybrid living constitution. With the immense difference, however, that his part therein is a factor of the development of traits, not of the mystical functioning of Life. A notable feature of this paternal heritage is that in women at middle-age (when the wane of reproductive power releases vital potential from maternal investments) not only may masculine physical traits emerge, but there may develop in them notable brain-capacities inherited from the father. Capacities inherent in them previously, but long inhibited in action by the normal female brain-Recessiveness.
VII
Every higher evolutionary differentiation results inevitably not only in progressive mutations in the traits of species, but, as well, in variations of the reproductive processes of such. When defects, physical or mental, are not reproduced in later generations true to Mendelian law, however, this is not abnormal, but is beautifully normal. Normality requires that defect—which is a deviation from The Normal—shall not be transmitted in any ratio whatsoever, but shall be corrected in a succeeding generation.