Neutral theory: the relative importance of drift and selection
It might seem like everywhere we look, we see evidence of natural
selection: organisms seem to be pretty well adapted to their
environments. But the neutral theory of molecular evolution suggests that most of the genetic variation in populations is the result of mutation and genetic drift and not selection.
Basically, the theory suggests that if a population carries several
different versions of a gene, odds are that each of those versions is
equally good at performing its job in other words, that variation
is neutral: whether you carry gene version A or gene version B does not
affect your fitness.
The neutral theory is easily misinterpreted. It does NOT suggest:
- That organisms are not adapted to their environments
- That all morphological variation is neutral
- That ALL genetic variation is neutral
- That natural selection is unimportant in shaping genomes
The main point of the neutral theory is simply that when we see
several versions of a gene in a population, it is likely that their
frequencies are simply drifting around. The
data supporting and refuting the neutral theory are complicated.
Figuring out how widely the neutral theory applies is still the topic
of much research.