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A tree frog's eyes are adapted for night vision. |
One
improvement at a time |
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| The pathway
by which evolution can produce complex structures has
been brilliantly explained in The Blind Watchmaker
by Richard Dawkins, a biologist at Oxford University.
The essence of Dawkins’s explanation is simple. Given
enough time (thousands of years) and material (millions
of individuals in a species), many genetic changes will
occur that result in slight improvements in a system or
structure such as the eye. However slight that improvement,
as long as it is genuine, natural selection will favor
its spread throughout the species over several generations. |
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Birds have highly
developed eyes, in
some ways even
more so than
humans. |
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Little by little, one improvement at a time, the system
becomes more and more complex, eventually resulting in
the fully functioning, well-adapted organ that we call
the eye. The retina and the lens did not have to evolve
separately because they evolved together. |
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Evolution
can be used as an explanation for complex structures if
we can imagine a series of small, intermediate steps leading
from the simple to the complex. Further, because natural
selection will act on every one of those intermediate
steps, no single one can be justified on the basis
of the final structure toward which it may be leading.
Each step must stand on its own as an improvement that
confers an advantage on the organism that possesses it. |
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