Biology Reference
In-Depth Information
natural selection is a highly dynamic process, but it is always at least one generation
behind changes in the environment.
Adaptation by natural selection often involves an increase in complexity because
in many environments, complexity increases fitness. In Victorian times many peo-
ple thought that evolution is
always
progressive - after all, it had produced human
beings such as themselves who are clearly superior to all other forms of life! But
this is another misunderstanding of how evolution works.
Complexity evolves only because it improves the fitness of the next generation in
the current environment. But if the environment changes, complexity may become
a disadvantage, and so natural selection can lead to a reduction in complexity. For
example, many parasites adapt to their environment by losing systems they no longer
need because their host can replace them. The tapeworm has no gut because it no
longer needs one in its present environment, living inside the digestive systems of its
host, but it evolved from a free-living worm that did have a gut. Some fish that live
inside caves have eyes that cannot see, because they have evolved from fish that had
functional eyes. Snakes have no functional legs but evolved from animals that did, as
shown by the presence of tiny hind limbs in some species. Many people, including
some biologists, find it difficult to abandon a progressive view of evolution, and
persist in using terms like “higher” and “lower”. Thus a moss is said to be a “lower
plant” and a daisy a “higher plant”. But every organism alive today is as much
evolved as any other organism. It is just that some are more complex than others.
Many people find this directionless aspect of the evolutionary process disagree-
able, because it offends our innate sense that human beings like us are so wonderful
that the process that produced us must be purposeful. This is really an example of
human arrogance and intentionality - we are conceited enough to feel we must be
special. Evolutionary theory, in contrast, says that we are just another animal, pro-
duced by the same process that has produced all the other animals, as well as the
plants, fungi and micro-organisms.
Another aspect of evolutionary theory that disturbs many people is the sheer
amount of pain and suffering that the mechanism of natural selection has produced
in the animal kingdom over hundreds of millions of years. Natural selection works
by eliminating the less fit, and the agents for this include disease, starvation and pre-
dation. It is for this reason that some biologists, such as David Attenborough, have
stated that they are not able to accept the idea that the living world was created by
an omnipotent, beneficient creator. Scientists who do accept this idea often respond
to this problem by saying that the actions of their creator cannot be understood by
mere humans.
Genetic Drift
Darwin thought that natural selection was the main cause of evolution but since his
time another mechanism has been discovered, called genetic drift. This process is
defined as the change in gene frequency between generations caused by random
sampling effects. The word “drift” is unfortunate because it could be interpreted to
