e 341,
1908.) Lastly, it may be recalled that in sterility we are almost
certainly considering a meristic phenomenon. FAILURE TO DIVIDE is,
we may feel fairly sure, the immediate "cause" of the sterility. Now,
though we know very little about the heredity of meristic differences,
all that we do know points to the conclusion that the less-divided is
dominant to the more-divided, and we are thus justified in supposing
that there are factors which can arrest or prevent cell-division. My
conjecture therefore is that in the case of sterility of cross-breds we
see the effect produced by a complementary pair of such factors. This
and many similar problems are now open to our analysis.

The question is sometimes asked, Do the new lights on Variation and
Heredity make the process of Evolution easier to understand? On the
whole the answer may be given that they do. There is some appearance of
loss of simplicity, but the gain is real. As was said above, the time
is not ripe for the discussion of the origin of species. With faith in
Evolution unshaken--if indeed the word faith can be used in application
to that which is certain--we look on the manner and causation of adapted
differentiation as still wholly mysterious. As Samuel Butler so truly
said: "To me it seems that the 'Origin of Variation,' whatever it is, is
the only true 'Origin of Species'" ("Life and Habit", London, page
263, 1878.), and of that Origin not one of us knows anything. But given
Variation--and it is given: assuming further that the variations are not
guided into paths of adaptation--and both to the Darwinian and to
the modern school this hypothesis appears to be sound if unproven--an
evolution of species proceeding by definite steps is more, rather than
less, easy to imagine than an evolution proceeding by the accumulation
of indefinite and insensible steps. Those who have lost themselves in
contemplating the miracles of Adaptation (whether real or spurious) have
not unnaturally fixed their hopes rather on the indefinite than on the
definite changes. The reasons are obvious. By suggesting that the
steps through which an adaptative mechanism arose were indefinite and
insensible, all further trouble is spared. While it could be said that
species arise by an insensible and imperceptible process of variation,
there was clearly no use in tiring ourselves by trying to perceive that
process. This labour-saving counsel found great favour. All that had
to be done to d