n
said that father and son ought to be thought of as half-brothers by two
different mothers, each being the product of the same strain of paternal
germ-plasm, but not of the same strain of maternal germ-plasm.
Biologically, the father or mother should not be thought of as the
_producer_ of a child, but as the trustee of a stream of germ-plasm
which produces a child whenever the proper conditions arise. Or as Sir
Michael Foster put it, "The animal body is in reality a vehicle for ova
or sperm; and after the life of the parent has become potentially
renewed in the offspring, the body remains as a cast-off envelope whose
future is but to die." Finally to quote the metaphor of J. Arthur
Thomson, one may "think for a moment of a baker who has a very precious
kind of leaven; he uses much of this in baking a large loaf; but he so
arranges matters by a clever contrivance that part of the original
leaven is always carried on unaltered, carefully preserved for the next
baking. Nature is the baker, the loaf is the body, the leaven is the
germ-plasm, and each baking is a generation."

When the respective functions and relative importance, from a genetic
point of view, of germ-plasm and body-plasm are understood, it must be
fairly evident that the natural point of attack for any attempt at race
betterment which aims to be fundamental rather than wholly superficial,
must be the germ-plasm rather than the body-plasm. The failure to hold
this point of view has been responsible for the disappointing results of
much of the sociological theory of the last century, and for the fact
that some of the work now carried on under the name of race betterment
is producing results that are of little or no significance to true race
betterment.

On the other hand, it must be fairly evident, from the pains which
Nature has taken to arrange for the transmission of the germ-plasm from
generation to generation, that she would also protect it from injury
with meticulous care. It seems hardly reasonable to suppose that a
material of this sort should be exposed, in the higher animals at least,
to all the vicissitudes of the environment, and to injury or change from
the chance of outward circumstances.

In spite of these presumptions which the biologist would, to say the
least, consider worthy of careful investigation, the world is full of
well-intentioned people who are anxious to improve the race, and who in
their attempts to do so, wholly ignore the ge