… and, to my embarrassment, I must admit that I had never heard of the Hardy-Weinberg equilibrium.
It was alleged in a recent PS discussion that Doug Axe had suggested that human evolution had stopped. I don’t know enough about Doug Axe to address that issue but it prompted me to review my very outdated understanding of evolutionary mechanisms and to consider what it would take for a population to reach some sort of evolutionary stasis. Then I stumbled upon this:
The Hardy-Weinberg equilibrium is a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors. When mating is random in a large population with no disruptive circumstances, the law predicts that both genotype and allele frequencies will remain constant because they are in equilibrium.
The Hardy-Weinberg equilibrium can be disturbed by a number of forces, including mutations, natural selection, nonrandom mating, genetic drift, and gene flow. For instance, mutations disrupt the equilibrium of allele frequencies by introducing new alleles into a population. Similarly, natural selection and nonrandom mating disrupt the Hardy-Weinberg equilibrium because they result in changes in gene frequencies. This occurs because certain alleles help or harm the reproductive success of the organisms that carry them. Another factor that can upset this equilibrium is genetic drift, which occurs when allele frequencies grow higher or lower by chance and typically takes place in small populations. Gene flow, which occurs when breeding between two populations transfers new alleles into a population, can also alter the Hardy-Weinberg equilibrium.
Because all of these disruptive forces commonly occur in nature, the Hardy-Weinberg equilibrium rarely applies in reality. Therefore, the Hardy-Weinberg equilibrium describes an idealized state, and genetic variations in nature can be measured as changes from this equilibrium state.
— from Hardy-Weinberg equilibrium | Learn Science at Scitable
It struck me that explaining the Hardy-Weinberg Equilibrium could be a very interesting way (and perhaps more memorable way) to explain the basic mechanisms of evolution to the novice. For me it seems to nicely pull together the bits and pieces of what I did already know. And for those evolution denialists who keep claiming that evolution “just can’t happen”, the Hardy-Weinberg Equilibrium nicely describes a context where there is a kind of stasis and “evolution doesn’t happen.”