getable
cell are derived from a common stock, and that the first living
organisms oscillated between the vegetable and animal form,
participating in both at once. Indeed, we have just seen that the
characteristic tendencies of the evolution of the two kingdoms, although
divergent, coexist even now, both in the plant and in the animal. The
proportion alone differs. Ordinarily, one of the two tendencies covers
or crushes down the other, but in exceptional circumstances the
suppressed one starts up and regains the place it had lost. The
mobility and consciousness of the vegetable cell are not so sound asleep
that they cannot rouse themselves when circumstances permit or demand
it; and, on the other hand, the evolution of the animal kingdom has
always been retarded, or stopped, or dragged back, by the tendency it
has kept toward the vegetative life. However full, however overflowing
the activity of an animal species may appear, torpor and unconsciousness
are always lying in wait for it. It keeps up its role only by effort, at
the price of fatigue. Along the route on which the animal has evolved,
there have been numberless shortcomings and cases of decay, generally
associated with parasitic habits; they are so many shuntings on to the
vegetative life. Thus, everything bears out the belief that vegetable
and animal are descended from a common ancestor which united the
tendencies of both in a rudimentary state.

But the two tendencies mutually implied in this rudimentary form became
dissociated as they grew. Hence the world of plants with its fixity and
insensibility, hence the animals with their mobility and consciousness.
There is no need, in order to explain this dividing into two, to bring
in any mysterious force. It is enough to point out that the living being
leans naturally toward what is most convenient to it, and that
vegetables and animals have chosen two different kinds of convenience in
the way of procuring the carbon and nitrogen they need. Vegetables
continually and mechanically draw these elements from an environment
that continually provides it. Animals, by action that is discontinuous,
concentrated in certain moments, and conscious, go to find these bodies
in organisms that have already fixed them. They are two different ways
of being industrious, or perhaps we may prefer to say, of being idle.
For this very reason we doubt whether nervous elements, however
rudimentary, will ever be found in the plant. What co