SCIENCE, NATURAL AND SOCIAL
provides light, but the light may be a will-of-the-wisp. However
pretty, however seductive, analogy remains analogy and never con-
stitutes proof. It throws out suggestions, which must be tested before
we can speak of demonstration.
But if non-scientists often overrate the importance of analogy,
scientists themselves tend to be over-cautious and to underrate its
potential value. Its value is especially great when the analogy is one
between closely related subjects. The analogy between the evolution
of different groups of animals is often surprisingly close, for the simple
reason that both the material and the conditions are essentially similar
throughout. None the less, unpredictable results are not infrequent.
The adaptive radiation of the marsupials in Australia was in its broad
lines similar to that of the placentals in the rest of the world; but the
placentals never developed large junipers like the kangaroo, and,
conversely, the marsupials produced no quick runners like horse or
antelope, and no freshwater fish-eaters like the otter. Again, the
parallelism in the social evolution of the quite unrelated ants and
termites is truly astonishing; yet the termites have never produced
grain-storers or slave-makers, while the ants have no system of second-
grade queens in reserve.
One further caveat before we pursue the biological analysis of man's
social existence. Human societies, though indubitably organic, are
unlike any animal organism in the mode of their reproduction.
Strictly speaking, they do not usually reproduce at all, but merely
perpetuate themselves. They exhibit no process of fertilization be-
tween living gametes, no distinction between mortal body and im-
mortal germ-plasm. They continue indefinitely by the aggregate
reproduction of their component individuals. In their development,
change of structural and functional pattern can be dissociated from
growth in a way impossible to a developing animal, and social
heredity operates via cultural transmission, not by the physical trans-
mission of material potencies of development. On the other hand,
the separation of phylogeny and ontogeny, the development of race
and the development of the individual, which is so evident in higher
animals, is blurred in social development to such an extent that the
two often coincide.
All analogies between the birth, development and death of civiliza-
tions or nations and of animal organisms must be very heavily dis-
counted because of this fundamental difference in the mode of their
reproduction and inheritance.
Now, with these facts in mind, let us look at some of the biological
analogies that lie near to hand. In the first place, there is the analogy