and it becomes possible to imagine how the
social cattle-- with their united front against an enemy, fierce
onslaught, and their general adaptation to prairie life-- have
differentiated from the ancestors of the slight and timid deer; how the
patient camel, with his storage hump, water storage, and feet padded
against hot sand, has been moulded by the necessity of desert life
from the same ancestral form. And so we may work back, and link
these forms, and other purely vegetarian feeders, with remoter
cousins, the ancestral hogs. Working in this way, we presently get a
glimpse of a possible yet remoter connection of all these hoofed and
mainly vegetarian animals, with certain "central types" that carry us
across to the omnivorous, and, in some cases, almost entirely
vegetarian bears, and to the great and prosperous family of clawed,
meat-eaters. And thus we elucidate, at last, a thread of blood
relationship between the, at present, strongly contrasted and
antagonistic deer and tiger, and passing thence into still wider
generalizations, it would be possible to connect the rabbit playing in
the sunshine, with the frog in the ditch, the dog-fish in the sea-waters
and the lancelet in the sand. For the transition from dog-fish to rabbit
differs from the transition from one species of deer to another only in
magnitude: it is an affair of vast epochs instead merely of thousands
of years.

Section 53. It would, however, be beyond the design of this book to
carry our demonstration of the credibility of a common ancestry of
animals still further back. But we may point out here that it is not a
theory, based merely upon one set of facts, but one singularly rich in
confirmation. We can construct, on purely anatomical grounds, a
theoretical pedigree. Now the independent study of embryology
suggests exactly the same pedigree, and the entirely independent
testimony of palaeontology is precisely in harmony with the already
confirmed theory arrived at in this way.

Section 54. It is in the demonstration of this wonderful unity in life,
only the more confirmed the more exhaustive our analysis becomes,
that the educational value and human interest of biology chiefly lies. In
the place of disconnected species of animals, arbitrarily created, and
a belief in the settled inexplicable, the student finds an enlightening
realization of uniform and active causes beneath an apparent diversity.
And the world is not made and dead like a cardb