CHAPTER XI

AS REGARDS HEREDITY

Problems of Heredity—Physiological Units—A Digression
— The Germ-Cells — Transmission of Acquired
Characters—Inconceivability—A Priori Argument—
Practical Conclusion

HEREDITY is the relation of genetic continuity which
links generation to generation. An inheritance is all
that the organism is or has to start with on its life-
journey in virtue of the hereditary relation to parents
and ancestors. In all ordinary cases, the inheritance
has its initial material basis in the egg-cell and the
sperm-cell which unite in fertilisation at the beginning
of a new life, and these two kinds of germ-cells,
which bear the maternal and the paternal contributions,
have their peculiar virtue of reproducing like from
like, just because they are the unchanged or very
slightly changed cell-descendants of the fertilised ova
from which the parents arose. A bud or a cutting
separated off from a living creature—tiger-lily or
potato, polyp or worm—reproduces an entire organism
like the parent, if the appropriate nurture-conditions
are available 5 and it can do so because it is a fair
sample of the parental organisation. Similarly a germ-
cell or two germ-cells in conjunction can develop into
a creature like the parent or parents, in virtue of being
the condensed essence of the parental organisation.
And the germ-cell is this because of its direct continuity
154habiting another medium, are at the same