Evolutionary pressure is the force with which
evolution directs the development of
species. In this case, ‘directs’ is a deceiving word, since the process is
blind.
While
evolution is
blind, it is not
random.
Evolution favors
organisms that survive and replicate themselves. Obviously, this creates an evolutionary pressure towards creatures that can sustain life and replicate it. Consequently, all
plants and
animals spend a great deal of their time maintaining their lives and producing new ones. Evolution does not ‘prefer’ organisms who reproduce, but organisms who reproduce will become more common, through their reproduction.
In giving
evolution a name, many people have taken on the confused belief that it is a
directed force. In actuality, it is the simple tendency of
stable molecules to remain longer than unstable ones. We see very few isotopes of
hydrogen with ten-thousand
neutrons, while most of the
universe is composed of
hydrogen lacking any
neutrons.
Any molecule that can produce copies of itself has an incredible advantage, in terms of the size of its
population. While most complex molecules form
randomly, and thus rarely, if a molecule can actively assemble a copy of itself it will be far more common. It does not, as a molecule, ‘want’ to replicate itself anymore than evolution as a force ‘wants’ to produce life. These things merely happen as a consequence of the physical properties of the universe.
Thus, stable molecules will eventually and randomly become prevalent and one of those random alterations will produce a molecule that can replicate itself: basically a
crystal. Then, given the fundamental principle that stable, reproducing molecules become more common, life as we understand it has developed. To go into the specifics of how this occurs is far beyond the reasonable content of this entry, but expressed with remarkable clarity and reason in
Richard Dawkin’s book:
The Selfish Gene.