The higher
types of both animals and plants appear plainly in response to a
lowering of temperature. This is the chief advantage of studying
the story of evolution in strict connection with the geological
record. We shall find that the record will continue to throw
light on our path to the end, but, as we are now about to
approach the most important era of evolution, and as we have now
seen so much of the concrete story of evolution, it will be
interesting to examine briefly some other ways of conceiving that
story.
We need not return to the consideration of the leading schools of
evolution, as described in a former chapter. Nothing that we have
seen will enable us to choose between the Lamarckian and the
Weismannist hypothesis; and I doubt if anything we are yet to see
will prove more decisive. The dispute is somewhat academic, and
not vital to a conception of evolution. We shall, for instance,
presently follow the evolution of the horse, and see four of its
toes shrink and disappear, while the fifth toe is enormously
strengthened. In the facts themselves there is nothing whatever
to decide whether this evolution took place on the lines
suggested by Weismann, or on the lines suggested by Lamarck and
accepted by Darwin.
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