How could there be white or purple beads in this bottle, when there were no white nor purple beads in the bottles from which it was filled?
But what of the variation amongst brothers and sisters?
That is easily understood. If the four colours in the ancestral bottles are evenly mixed, the grandchildren bottles will vary from their ancestors, but not from each other.
As we know that brothers and sisters do vary from each other, we must conclude that the hereditary qualities are not evenly mixed.
WHERE DO OUR NATURES COME FROM?
For the scientific explanation of this fact I must refer you to The Germ Plasm, by Weissmann.
For our purposes it is enough to know that brothers and sisters do vary from each other, and that they so vary because the ancestral qualities are not evenly distributed amongst the "sperms" and the "ova." On this head our own knowledge and observation do not leave any room for doubt.
It is as if in the case of our marriage of Red-Blue and Black-Yellow there were three child-bottles, of which one got more red and yellow, one more blue and red, and one more yellow and blue than the others. So that the three brother-bottles would differ from their fore-parents and from each other.
And as it would be foolish to blame the second bottle for having less red in it than the first, so it is foolish to blame a human child for having less intellect or less industry than his brothers.
If you refer to the masterly description of the impregnation of the ova given in Haeckel's great work, The Evolution of Man, you will find that the heredity of brothers is largely a matter of accident. See the plate and explanation on page 130 in the first volume.