Is Human Evolution Over?

Abstract

Humans have always been interested in predicting the future and one of the best ways of doing that is to examine the past. In order to predict the future of human evolution, I shall therefore examine what we know of what has shaped it in the past and identify the trends that illuminate what is to come. According to evolutionary theory there are three elements to be considered: mutation, natural selection and random variation. Interestingly, studies of the incidence of mutation among the offspring of survivors of the atomic bomb dropped on Nagasaki showed no increase in the mutation rate, despite exposure to high levels of mutagenic radiation. They did confirm that the male germ-line has a higher mutation rate than the female and it is also known that older men have more mutations in their sperm than young men. However, there is no evidence that, globally, the mean age of fathers is increasing, indeed it should fall as countries become more developed. Natural selection can be shown to have acted on humans to produce the phenotypic diversity evident today. But natural selection requires competition between genotypes and since, in developed countries, families are roughly the same size and survival rates through childhood are extremely high, natural selection is no longer acting. Lastly, the biggest influence on random variation is population size. This was a major factor in human history when we lived in much smaller groups and random variants could spread rapidly. In a globalising world, the opportunity for this is greatly reduced. Hence, although human evolution has not yet ceased, it will proceed extremely slowly.