f 'accidental variations' to those peculiarities with which an animal
is born, Darwin does not for a moment mean to suggest that they are not
the fixed outcome of natural law. If the total system of the universe
be taken into account, the causes of these variations and the visible
environment which preserves or destroys them, undoubtedly do, in some
remote and roundabout way, hang together. What Darwin means is, that,
since that environment is a perfectly known thing, and its relations to
the organism in the way of destruction or preservation are tangible and
distinct, it would utterly confuse our finite understandings and
frustrate our hopes of science to mix in with it facts from such a
disparate and incommensurable cycle as that in which the variations are
produced. This last cycle is that of occurrences before the animal is
born. It is the cycle of influences upon ova and embryos; {224} in
which lie the causes that tip them and tilt them towards masculinity or
femininity, towards strength or weakness, towards health or disease,
and towards divergence from the parent type. What are the causes there?

In the first place, they are molecular and invisible,--inaccessible,
therefore, to direct observation of any kind. Secondly, their
operations are compatible with any social, political, and physical
conditions of environment. The same parents, living in the same
environing conditions, may at one birth produce a genius, at the next
an idiot or a monster. The visible external conditions are therefore
not direct determinants of this cycle; and the more we consider the
matter, the more we are forced to believe that two children of the same
parents are made to differ from each other by causes as
disproportionate to their ultimate effects as is the famous pebble on
the Rocky Mountain crest, which separates two rain-drops, to the Gulf
of St. Lawrence and the Pacific Ocean toward which it makes them
severally flow.

The great mechanical distinction between transitive forces and
discharging forces is nowhere illustrated on such a scale as in
physiology. Almost all causes there are forces of _detent_, which
operate by simply unlocking energy already stored up. They are
upsetters of unstable equilibria, and the resultant effect depends
infinitely more on the nature of the materials upset than on that of
the particular stimulus which joggles them down. Galvanic work, equal
to unity, done on a frog's nerve will discharge