This stems from the assertion that “Human evolution has stopped.” I particularly take interest in this for a number of falsehoods build into the statement. Many people take offense at the fact that it is blatantly incorrect (lactase persistence? No, what about sickle trait? No, how about human diversification and radiation is actually happening FASTER?) while I take offense at the notion that evolution, in living, reproducing, and dying organisms can stop at all. The principle is simple: every single human has numerous mutations not present in either parent. In turn, each parent has numerous novel mutations as well which are passed along to the offspring. Evolution is not dependent upon selection of traits, completely silent genes will have mutations which will drift in frequency among a given population. Different parts of the DNA structure are more likely to undergo mutation than others, resulting in even more variation. In regards to actively transcribed genes, this too can be subject to selection even if not obviously apparent.
Fun tangent. If women had narrower hips, prior to the introduction of medically safe c-sections, they would often experience more complications during childbirth and frequently died as a result either of the childbirth or the unsafe c-section. It would be interesting (and has possibly already been studied) whether or not female hip morphology is changing due to the rise in prevalence and survival rate from this procedure as compared to archaeological specimens.
Anyway, back to the falsehood. The appearance of novel new traits is a function of population size. The larger the population size, the more likely a given randomly appearing mutation will occur. This where evolution would actually SPEED UP in humans. The falsehood arises from the notion that in large populations, the novel mutations are “outvoted” by the more prevalent alleles. This, however, assumes no selection, and even so, it is still possible (but unlikely) that an allele will become more prevalent in the population. It is made more likely if the mutation arises on multiple occasions or has a selective pressure in favor of it, even if only for a brief duration.
I have yet to hear anyone state other species have “stopped evolving” other than the “living fossils.” This would be to ignore the mountains of evidence that blatantly demonstrates evolution is, in fact, still occurring in these lineages. The only way for evolution to stop for a species is when that species has become extinct. Even in the obligate parthenogenetic lizards, they do still evolve. They raise interesting questions for how we define a “species,” but the allelic frequency within a population changes.
Evolution happens, like it or not. Even if we were to ACTIVELY try to prevent allelic shift within a human population, the ONLY way to do so would be to completely synthesize clones (not just through stem cells as these have replication fidelity issues). Even then, we are limited by the fidelity of the synthesis equipment we would use and these will, undoubtedly, have mutations of some kind. Before we can do that, we must understand many more aspects of genetics and development.
My next post will be a few days away as it is a book review and I must finish the book first.
I hope you’ve enjoyed my falsehoods, a new page will be located at the top linking to all of my falsehoods.