Charles Darwin 11THE “ORIGIN OF SPECIES.”Darwin referred to theOrigin as “one long argument,” and this is the way to
read it. For all that it is written in a friendly, almost folksy style, it is a very
sophisticated piece of reasoning that reflects the influences that Darwin felt when
he was learning to be a scientist in the 1830s. Mention has already been made
of Newton. The shadow lay over everything. Darwin set out to find a force, the
equivalent in biology of gravitational attraction in physics, and in natural selection
he thought he had found it. But one could not, as it were, just plonk the force
into the discussion without preparation or argument. The authorities on scientific
methodology, primarily Herschel and Whewell, agreed that really one ought to be
building a connected system of laws — what in the twentieth century we learned
to call hypothetico deductive systems — and that cause must be located within
these.
But what kinds of causes? Only the best, what Newton somewhat mysteriously
labeled “true causes” orverae causae. Now came the question of what constitutes
avera causa— what is the mark that one has one? Here Herschel and Whewell
parted company. Herschel [1830] took a more empiricist approach, arguing that
one must have experience of such causes or analogous phenomena like them. That
was a major reason why he liked Lyell’s theory of climate. We may not have
experienced the past, but we have experienced the Gulf Stream. Whewell [1840]
took a more rationalist position. Rather than arguing from experience, he wanted
to argue to experience. We may never have encountered a catastrophe or anything
like it, but if today’s aftereffects point to one, then so be it. He argued that
true causes are located at the heart of what he called “consilience of inductions.”
Unification. Many areas point to a hypothesis; the hypothesis explains many areas.
The debate over geology on one side, this was no mere academic exercise. The
wave theory of light was now succeeding beyond all dreams and the methodologists
were trying to explain the success. No one could see waves, so why should anyone
think them true causes? Herschel [1827] virtually bent himself in half trying to
think up analogies — literally, pieces of string and sealing wax — to show how
interference patterns could take place. Whewell [1840], rather smugly, sat back
and argued that the effects are what counts. Who cares if anyone has seen a light
wave or not?
The young Darwin took all of this in, and decided that he had to show his force
of natural selection to be avera causa. But empiricist or rationalist? Darwin
covered himself in theOriginby going both routes! First he introduced the topic
of artificial selection, showing just how powerful it could be and how far it is
possible to change organisms to one’s will.
The great power of this principle of selection is not hypothetical. It is
certain that several of our eminent breeders have, even within a single
lifetime, modified to a large extent their breeds of cattle and sheep....
Breeders habitually speak of an animal’s organization as something
quite plastic, which they can model almost as they please. If I had