Tool Module: What
Is Evolution? People have always
been trying to explain the origin and profusion of the forms of life on Earth.
Over the centuries, many explanations have been offered. One was fixism: the doctrine
that the species living on Earth have always been the same and have not evolved
since their creation. Another was Lamarck's theory of the transmission of acquired
characteristics, based on the idea that populations are gradually transformed
as the direct result of the environmental constraints they face. But
the theory that has ultimately been confirmed by the facts is Darwin's, that species
evolve through mutations, followed by natural selection. For nearly two centuries now, so many confirming observations have
been accumulating that we can now state that evolution is a phenomenon that has
in fact occurred and continues to occur today. All the evidence, from disciplines
as diverse as paleontology, genetics, anatomy, chemistry, and geography, converges
to confirm the existence of evolution. Scientists have now discovered that natural selection was not the only
mechanism of this evolution. But they can state that all living species are the
product of evolution and are derived from common distant ancestors. Ironically,
it is often the great diversity and complexity of the forms of life that makes
the idea of evolution so difficult for so many people to accept. They find it
hard to imagine that random genetic mutations, combined with a natural selection
mechanism, could be solely responsible for such complex beings as humans, and
such complex organs as their brains. They find it more logical to believe that
the human brain was “designed” by some divine engineer — hence
the persistent attraction of creationism. But the human brain was not
designed by any engineer. It is a product of evolution, a series of small changes
that have accumulated gradually over very long periods. And that is the real reason
that people have so much trouble with the idea of evolution: the geologic time
scale on which it takes place. On the time scale of a human life, to design a complex machine, someone
must first decide on its function, then draw up plans for a mechanism that can
perform that function, and then manufacture that mechanism. But that is not how
the process of evolution produced the human brain. Evolution built on top of what
it already had to work with, rather than starting from zero. On the scale of a
human life, this approach is totally inefficient; it would be like trying to build
a car by modifying a wheelbarrow. But on the geologic time scales on which life
evolves, it works just fine. Here it is important to stress that evolution
does not have a plan. Human beings are an accident of evolution, just like carnivorous
plants or the duck-billed platypus. The larger brains that appeared late in the
course of evolution are not “better” than the smaller ones that came
before them. Evolution is an ongoing exploration of the variability created by
chance mutations in existing forms of life. When a trait appears later in evolution,
it just means that evolution is trying something new, not that it has necessarily
found a better alternative. In fact, when you consider how the activities of some groups of humans
are threatening the planet Earth today, you may well wonder whether the advent
of our species was really such a great idea on evolution's part. |