Sorry for the clickbait title. But seriously, do populations closer to the equator undergo more frequent genetic mutations?
If evolution is partially driven by random mutations, and if sunlight is one source of mutations, do populations of people and other species subjected to more sunlight over time undergo quicker or more substantial mutations?
Could it be said that darker-skinned equatorial populations have evolved more than people in northerly latitudes, based on genetic diverge from the last common set of ancestors?
You need to distinguish somatic mutations from germline mutations. UV causes somatic mutations in surface cells that are exposed to sunlight. But somatic mutations are not passed on to the next generation, so they are irrelevant to evolution (except perhaps indirectly, to the extent that they might impose selection pressure for improved DNA damage repair mechanisms). So far as I’m aware, UV is not a significant cause of mutagenesis in the germline.
Also, people with darker skin are less likely to get skin cancer with a given amount of sun exposure, (presumably) because the melanin in their skin protects them from it. So, while darker-skinned peoples are more likely to live near the equator and (presumably) more likely to get more exposure to the sun, it is also (presumably) less likely for an equal amount of sun exposure to affect them. I presume that this means that a darker-skinned person living near the equator is no more likely to get skin cancer than a lighter-skinned person living far from the equator. And as Riemann pointed out, there’s no reason to think that the sun’s rays cause germline mutations.
And just to state this more precisely, all mutations are random, and random mutations are the only source material for evolutionary change. Mutations arise randomly in individual organisms within a population.
Evolution occurs at the population level. What subsequently happens to those randomly-arising mutations may be driven by either random or non-random processes in the population.
Most mutations are neutral, having no effect on the phenotype. Neutral mutations may either be lost from the population or become fixed in the population by chance, a process called genetic drift.
Only the minority of non-neutral mutations (mutations with a phenotype) are influenced by natural selection, a non-random process.
While it is true that the vast majority of human genetic variation exists in sub-Saharan African populations, this is due to the bottleneck effect of various groups leaving Africa rather than increased mutation rates in Africa.
This is not really correct, because it’s important to remember that evolutionary change and evolutionary adaptation are not synonymous.
Most DNA mutations are neutral (no phenotype), so at the molecular level there is a baseline rate of evolution that is proportional to the mutation rate.
Among the minority of mutations that are non-neutral (with a phenotype), most are deleterious, and tend to be removed by purifying selection. So the predominant effect of selection pressure (when it has any effect) is actually to slow evolutionary change.
Only for the tiny minority of mutations that are beneficial does natural selection work to favor the change in the population, leading to adaptive evolution.
So it’s true that the biggest spur to interesting evolutionary change, i.e. adaptation, is selection pressure. But (at the molecular level, at least) only a tiny proportion of the evolutionary change is adaptive change.
It’s a very common misconception that evolution only means adaptation. The fact that this is not so is of fundamental importance, it is not splitting hairs.
Without understanding evolution through genetic drift, we cannot possibly make sense of most speciation or the bottleneck effect.
The Neutral Theory was, at the time, a radical idea. It underpins the entire field of molecular phylogenetics.
I assume what you mean by this is that the populations that left Africa contained only a portion of the genetic diversity present there when they left. To say this another way, Africa has higher genetic diversity in part because it retains some very old lineages that were not involved in the colonization of the rest of the world. Lineages outside of Africa have had less time to accumulate genetic diversity.
As has been said, what we are interested in here is mutations to germ line cells, not somatic cells. Since germ line cells are contained in the gonads and protected by opaque tissue, one would not expect UV to cause significant mutations in them. UV mostly causes mutations in somatic skin cells.
Also, any UV would mutate only the surface layer, it does not penetrate very deep - obviously most ovaries are well shielded and probably most testicles (plus in shade/dark) .
Along with altitude, would being nearer the north magnetic pole (or south) as well as with altitude expose someone to stronger cosmic radiation and the risk of deep tissue/germ line mutations. (Or is the difference with particles that reach the round depending on the magnetic field not that significant?)
My understanding is that Caucasian and Asian populations actually have higher levels of genetic load than Africans due to the Out-of-Africa population “bottleneck” that occurred.