In spite of the role played by stochastic events in
the phylogenetic history of birds, it would be mistaken to say
that wings are not teleological features. As pointed out earlier,
there are differences between the teleology of an organism's adaptations
and the nonteleological potential uses of natural inanimate objects.
A mountain may have features appropriate for skiing, but those
features did not come about so as to provide skiing slopes. On
the other hand, the wings of birds came about precisely because
they serve for flying. The explanatory reason for the existence
of wings and their configuration is the end they serveflyingwhich
in turn contributes to the reproductive success of birds. If wings
did not serve an adaptive function they would have never come
about, and would gradually disappear over the generations.
The indeterminate character of the outcome of natural selection
over time is due to a variety of nondeterministic factors. The
outcome of natural selection depends, first, on what alternative
genetic variants happen to be available at any one time. This
in turn depends on the stochastic processes of mutation and recombination,
and also on the past history of any given population. (What new
genes may arise by mutation and what new genetic constitutions
may arise by recombination depend on what genes happen to be presentwhich
depends on previous history.) The outcome of natural selection
depends also on the conditions of the physical and biotic environment.
Which alternatives among available genetic variants may be favored
by selection depends on the particular set of environmental conditions
to which a population is exposed.
It is important, for historical reasons, to reiterate that
the process of evolution by natural selection is not teleological
in the purposeful sense. The natural theologians of the nineteenth
century erroneously claimed that the directive organization of
living beings evinces the existence of a Designer. The adaptations
of organisms can be explained as the result of natural processes
without recourse to consciously intended end-products. There is
purposeful activity in the world, at least in man; but the existence
and particular structures of organisms, including humans, need
not be explained as the result of purposeful behavior.
Some scientists and philosophers who held that evolution is
a natural process erred, nevertheless, in seeing evolution as
a determinate, or bounded, process. Lamarck (1809) thought that
evolutionary change necessarily proceeded along determined paths
from simpler to more complex organisms. Similarly, the evolutionary
philosophies of Bergson (1907), Teilhard de Chardin (1959), and
the theories of nomogenesis (Berg 1926), aristogenesis
(Osborn 1934), orthogenesis, and the like are erroneous
because they all claim that evolutionary change necessarily proceeds
along determined paths.
These theories mistakenly take embryological development as
the model of evolutionary change, regarding the teleology of evolution
as determinate. Although there are teleologically determinate
processes in the living world, like embryological development
and physiological homeostasis, the evolutionary origin of living
beings is teleological only in the indeterminate sense. Natural
selection does not in any way direct evolution toward any particular
kind of organism or toward any particular properties.
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