Very layman question incoming… (for entertainment purposes only, I probably won’t reply since I lack the academic knowledge and if I do it’ll probably be a question)
The scholars say that we all originated from Africa, before we migrated out all over the world. Doesn’t that mean we ended up with a smaller genetic variety in those localized areas? Does that translate into inferior quality of humans (analogous to interbreeding)? Does that mean our entire human species is actually “inferior” until our children’s children’s (etc.) become more mixed and mixed?
No. We still get the benefit of beneficial mutations popping about. Also, very few human populations are truly that isolated. Native Americans might come closest, and even they showed a fair variety of genetic diversity (and it’s not even true for them anymore with the influx of people from around the world).
No matter how “localized” a population is, you get an influx of genes from everywhere after a while. Looking at the locals from one end of the old silk road to the other should be proof of that.
Also, we can’t get “back” to our ancestors via mass breeding of people from geographical diverse areas. That assumes we somehow “average” to the same people we were tens of thousands of years ago, which is not even true. I brought this up in another thread a while ago, but we’re measurably physically different than our ancestors in a few ways. Evolution is still ongoing, even in humans.
Yes. There is more genetic diversity in Africa than all the rest of the world. But, keep in mind that we were still evolving after we left Africa, so we non-Africans have much more genetic diversity than our 60k years ago ancestors who left there.
Less diverse genetically is generally worse than more divers, but you can’t put an “inferior” or “superior” label on it unless you define the environment you’re talking about. Light skinned people are “superior” when it comes to living in far northern climes, but darker skinned people are “superior” in more southerly climes.
The big question, though, is what happens when there’s a significant environmental change, and that all depends on the details of the change.
No. See above.
As for looking like our ancestors, we don’t even know what they looked like, so it’s hard to say what we’d be shooting for. However, there have been many mutations added to our genome in the last 60k years or so, and we don’t lose those by interbreeding. So, no, we can’t breed ourselves back to looking like we did 60k years ago, although it’s possible that a totally mixed population would look closer to what our ancestors did than most of us do today. Or not, depending on how things turned out. We just don’t know.
One thing we do know, is that San bushmen seem to be one of the oldest populations on Earth, and they have an intriguing phenotype where you see elements of differing populations around the world-- medium dark skin, high cheekbones, and epicanthic folds. They look quite distinct from other African populations.
According to geneticist Spencer Wells, we have living descendants with genetic markers of the most recent common ancestor for just about all non-Africans. See here:
You seem to be imagining that as people spread out from Africa, different groups took different portions of the original human genetic diversity in different directions, to different places. There is no reason to think that it was like that to any significant degree. More likely, it would be closer to the truth to say that all the groups of people who spread out from Africa had fairly similar genetic endowments, and differences arose later due to natural selection (and genetic drift) within in the groups in their various newly found environments.
Most likely homo sapiens is more genetically diverse now then when we first left Africa. A thorough mixing of current races would in no way get us back to how our ancient ancestors were.
Not on a genetic level, but humans could be back bred to resemble early humans. People have attempted to back breed aurochs. It’s not perfect, and its DNA is not that of an auroch, but we can get into the ball park in the looks department.
Maybe so, but my impression was that the OP thought we could get there simply by thoroughly intermixing all current human populations. What you are talking about would be more like a very deliberate program of selective breeding aiming at a predetermined goal.
By comparison: All dogs descend from wolves. Some dogs look very, very different from wolves, in a wide variety of ways. If you take a bunch of random dogs of all different breeds and mix them all back together, you get something like a Carolina yellow dog, or a dingo. A dingo isn’t nearly as divergent from a wolf as a Chihuahua is, but it’s still pretty different.
Chronos, you bring up an interesting example.
Dogs were bred based upon characteristics chosen by humans.
(In some ways, the same can be said of humans, by I digress.)
It has been posited that the time of divergence from the original trait mix in dogs was something on the order of 12,000 years. Somebody please correct me as I am probably wrong. Is it possible to recreate the ‘ur-dog’ through breeding?
I dare say not. And our species diversity appears to be greater than that of canines. Different cohorts lived in geographically isolated regions for thousands of years. We, as a species, developed quite a number of divergent traits. I genuinely doubt that we could return to the phenotype of our ancient common ancestors even through a horrible eugenics type of experiment.
But, I can say that in my lifetime, I have seen multi-generational multi-racial families form and grow and the results have been rather remarkable. We may not return to the past, but the future appears to be a brighter place because of such unions.
One thing to consider is white people. While there isn’t just one gene that makes a person white, there is one particular gene that all white people of European descent have. It’s a gene that is supposed to regulate the production of melanin in the skin. All European whites have a defective copy of this gene, so they are supposed to produce melanin and have darker skin but it doesn’t work properly (so in a way, all European white people are just defective black people). The best explanation I have heard for why this particular defect became so popular very quickly is that basically the climate of northern Europe sucks. People with this defective gene don’t have as much protection from sunlight, so in an area where sunlight is scarce, these people absorb sunlight and make vitamin D better, giving them an advantage.
This genetic “defect” works against people who live in an area like the African plains where our ancestors are from, since being overly sensitive to sunlight actually works against you in an area that has so much sun.
If you mix the genetic material from white people into your mix, then some portion of the population will get this defective copy of it, giving them lighter skin, which our ancestors did not have. In other words you will be diverging your “mix” away from our ancestors rather than getting closer to them, which seems to be the exact opposite of what the OP is trying to accomplish.
Incidentally, lighter skinned Asians do not have the defective European gene, which indicates that lighter skin actually evolved at least twice completely separately from each other, though probably for the same reason (better survival in areas of less sunlight).
This of course is just one example, but it’s a very common and easily recognizable example of how our genetic populations diverged once we left Africa.
Why do some people with one European white parent and one dark black African parent end up sort of in-between brownish? Do they have the gene you describe or not?
They have that gene from their European parent and the functioning gene from their African parent. But in this case having just one functioning gene and not two means getting just half the melanin production.
engineer and naita’s answers are essentially correct, but to clarify and expand a bit–
There is not a single gene for skin color. Everyone has several genes that regulate melanogenesis, each of which come in several alleles, and each of which operates with incomplete dominance between the versions of each gene that a child receives from each parent. It’s not a simple on/off switch.
However, the most notable European mutation in the equation is the threonine allele of the SLC24A5 gene. Having two, or one, or no copies of this allele (versus the ancestral alanine version) is a major factor in determining skin tone, but the effects of the other genes still combine to produce a range of results for each of the three sets.
Huh. I had understood that that was the origin of Carolina dogs and dingos, but based on some reading just now, it looks like those two breeds actually represent relatively early divergences from the rest of the domestic dog lineages. Which does not necessarily imply that what I said was wrong, but it certainly removes the reason why I thought it was right.
As in, it is still possible, perhaps even plausible, that an omnimongrel might end up looking something like a dingo. But there’s no compelling reason to think that must be the case.
Yes, you are correct about that. BUT… that is an anomaly. Generally, when you let you domestic animals run wild and reproduce, they do revert to the ancestral form. Except for dogs. And that is not well understood. Some scientists hypothesize that the ancestor of all domestic dogs did indeed look like what is generally called pariah dog.
I’ll have to take that last sentence to the woodshed for a while and see what it means.