20 CHAPTER 112]. This example illustrates how evolutionary hypotheses can be tested, and
it also shows how they can predict and reveal aspects of biology we would not
otherwise have expected.Philosophical Issues
Thousands of pages have been written about the philosophical and social implica-
tions of evolution. Darwin argued that every characteristic of a species can vary and
can be altered radically, given enough time. Thus he rejected the emphasis on dis-
tinct “types” that Western philosophy had inherited from Plato and Aristotle and put
variation in its place. Darwin also helped replace a static conception of the world—
one virtually identical to the Creator’s perfect creation—with a world of ceaseless
change. It was Darwin who extended to living things, including the human species,
the principle that change, not stasis, is the natural order. In contrast to traditional
views that elevated the human species to a special position, distinct from other liv-
ing things, Darwin began the trend to see humans as part of the natural world, a
species of animal (though a very remarkable species, to be sure!) subject to the same
processes as others, including natural selection.
Darwin has been credited with making biology a science, for he proposed
to replace supernatural explanations in biology with purely natural causes. His
theory of random, purposeless variation acted on by blind, purposeless natural
selection provided a revolutionary new kind of answer to almost all questions
that begin with “Why?” Before Darwin, both philosophers and people in general
answered questions such as “Why do plants have flowers?” or “Why are there
apple trees?”—or diseases, or sexual reproduction—by imagining the possible
purpose that God could have had in creating them. This kind of explanation was
made completely superfluous by Darwin’s theory of natural selection. The adap-
tations of organisms—long cited as the most conspicuous evidence of intelligent
design in the universe—could be explained by purely mechanistic causes. For
evolutionary biologists, the pink petals of a magnolia’s flower have a function
(attracting pollinating insects) but not a purpose. The flower was not designed in
order to propagate the species, much less to delight us with its beauty, but instead
came into existence because magnolias with brightly colored flowers reproduced
more prolifically than magnolias with duller flowers. The unsettling implication
of this purely material explanation is that, except in the case of human behavior,
we need not invoke, nor can we find any evidence for, any design, goal, or pur-
pose anywhere in the natural world.
All of modern science employs the way of thought that Darwin applied to biol-
ogy. Geologists do not seek the purpose of earthquakes or plate tectonics, nor
chemists the purpose of hydrogen bonds. The concept of purpose plays no part
in scientific explanation.01_EVOL4E_CH01.indd 20 3/23/17 8:43 AM