Now, could we blame the "child" bottle for having red and blue beads
in it; or could we blame the "child" bottle for having no yellow and no
green beads in it?
But that is an example of a simple mixture of two ancestral strains. We
have to do with mixtures of millions of strains.
Let us carry our illustration forward another generation.
Take our blue and red "child" and marry him to the child of a black
bottle and a yellow bottle.
This gives us a marriage between Red-Blue and Black-Yellow.
The "child" bottle mixed from these two bottles of double colours will
contain four colours.
He will "inherit" from grandfather Red and grandmother Blue, from
grandfather Black and grandmother Yellow, and from father Red-Blue and
mother Black-Yellow.
He will be like the six fore-parents, but different from each of them.
Can we blame this "child" bottle for being made up of red, blue, black,
and yellow? Can we blame it for having no purple nor white beads in its
composition? No. These colours were mixed _for_ the child, and not _by_
it.
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.