SELECTION 205

here another example of his biological insight* That
Spencer was not far from the idea of a struggle between
hereditary units, we see from the following passage: " In
the fertilised germ we have two groups of physiological units,
slightly different in their structures. These slightly different
units severally multiply at the expense of the nutriment
supplied to the unfolding germ—each kind moulding this
nutriment into units of its own type. Throughout the
process of development the two kinds of units, mainly
agreeing in their proclivities and in the form which they tend
to build themselves into, but having minor differences, work
in unison to produce an organism of the species from which
they were derived, but work in antagonism to produce copies
of their respective parent-organisms. And hence ultimately
results an organism in which traits of the one are mixed with
traits of the other; and in which, according to the pre-
dominance of one or other group of units, one or other sex
with all its concomitants is produced " (Principles of Biology 9
vol. L, revised ed., p. 315).

While Spencer had this wide appreciation of the
scope of selection, he firmly held that biologists
burdened it unjustifiably by disbelieving in the trans-
mission of acquired characters, and, as we have seen,
he gave a number of examples of phenomena which he
believed the Darwinian theory minus the Lamarckian
factor was quite inadequate to interpret. He went
the length of saying: " Either there has been inherit-
ance of acquired characters or there has been no evolu-
tion." Spencer indicated three general difficulties or
limitations besetting the theory of Natural Selection.

(l) "The general argument proceeds upon the
analogy between natural selection and artificial selec-
tion. Yet all know that the first cannot do what the
last does. Natural Selection can do nothing more
than preserve those of which the aggregate characters
are most favourable to life. It cannot pick out thoserganismus" .