GAE and Africans

As I understand it, GAE could have lived in any place and at any time prior to the existence of the MRCA of everyone alive at the time of the birth of Jesus. How could that be ruled?

No, it assumes that some of them were successful. And it assumes that within a village there is no barrier to interbreeding. What’s the problem with that?

It merely assumes that there is some level of migration between neighboring villages. What’s the problem with that?

It’s not necessary for everyone to move, just a few. Again, all you have to suppose is that there is free intermarriage within villages and some intermarriage between neighboring villages, with no complete breaks. Is that really a problem?

Not clear on the question. The GAE hypothesis that @swamidass advances could be falsified (by which I mean rendered statistically unlikely) if a simulation of migration showed that there was a low probability of the descendants of a single couple encompassing the entire human population within 4000 years. It could of course be saved by adding auxiliary hypotheses, for example that God pushes the migration by direct intervention; but that’s true for any falsified hypothesis.

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I don’t think that is the case. AFAIK, there is no stipulation that Adam and Eve lived within the past 4000 years. I don’t think it is even necessary that they have been modern H. sapiens. Again, by my understanding, the only stipulation is that they be ancestors of every human who was alive when Jesus was born. And there are literally countless organisms that could fit the bill, though I do think there is an assumption that they at least be primates that have a reasonable resemblance to us.

But @swamidass can confirm.

Yeah. I see no reason why that assumption is true.

No issue with that, but I see no reason why the descendants were always part of the migrants.

What if at some point none moved, but some other person’s descendants did?

No, but, again, why must the descendants of A&E be the one’s intermarrying within and between villages? And why must the descendants of A&E predominate in a village following initial intermarriages?

That’s right. The scenario is that they lived 6000 years ago and achieved universal ancestry 2000 years ago.

You could have all sorts of scenarios, but that isn’t the one @swamidass is proposing.

What’s wrong with it?

Not always, just sometimes. Remember, there’s 4000 years of available time. And remember that eventually the descendants consist of everyone in the donor population.

How does GAE make it to the Americas?

There is nothing wrong with the assumption, but I don’t see how it always held true for the descendants of A&E.

This makes no sense. A&E cannot become the genealogical ancestors if their descendants did not migrate to every village in Africa and intermarry with members of those villages.

True, but its also likely they weren’t successful in some African tribes and the modern descendants of those tribes aren’t genealogical descendants of A&E.

Explained many times. Through Siberia; there has always been communication across the Bering Straits.

Why not?

True. So why wouldn’t they? Remember that ancestry spreads within a village. As long as there’s some rate of migration, eventually one of the people moving from village A to village B will be a descendant. And the process repeats.

Why is that likely? It’s possible if the migration rate is low enough. But is a low enough rate credible? You need to look at the assumptions of the references.

I don’t understand that to be an essential aspect of the model, though it might be the scenario that @swamidass believes to be most likely. But I could well be wrong.

Cultural barriers like that detailed in the BBC report can hinder intermarriage; in this case, “freeborns” and “slaves”. Interestingly, the article is about one Igbo tribe, Anambra. It also mentions the “osu”: if a descendant of A&E became one, they would be shunned for life within their community. I am not saying these things existed 4000 years ago, but something similar and that could hinder intermarriage between the descendants of A&E or any other person at the time.

Cultural barriers come to mind. Africa is a place where cultural factors weigh heavily on decisions involving intermarriage.

The same reasons why not everyone who existed in the past is our genealogical ancestor today.

Remember that it could also not spread for different reasons.

An what if the descendants of A&E aren’t the ones who made the trips?

Cultural barriers, fertility issues, etcetera. The same factors that excluded certain individuals in the past from being my genealogical ancestors.

Yes, but only if it is the sole or dominant factor. In Africa, I don’t see that being the case. I think cultural factors would have heavily influenced this.

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In order to work they would have to entirely prevent interbreeding (which is not quite the same as intermarriage, incidentally). So we’re back to complete isolation.

The major reason for that is that some people didn’t have children. But most people did.

Remember that it doesn’t take much leakage around these social barriers to spread genealogical ancestry.

How likely is that, considering that everyone in the source village is eventually one of those descendants?

Those cultural factors would need to produce 100% isolated populations. Would they?

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Not complete isolation but lineage extinction.

And that could have befallen some descendants of A&E in some parts of Africa.

True, but those social barriers could have been really efficient in some cases.

Entire villages can get wiped out during wars or disease outbreaks.

No, they would need to extinguish lineages.

I don’t think we should keep up with this discussion because its pointless. Its likely all modern Africans are genealogical descendants of A&E. Its also likely they are not. I guess we can pick whatever option appeals to us. Thanks for the spirited discussion John, even though I wished it was @swamidass I had this dialogue.

Those can’t both be likely, under my understanding of the term. Again, I suggest you consult the references to the simulations that @swamidass is using as support for his hypothesis. See if you have reason to doubt the various migration paremeters used. You might also investigate the effects of changing those parameters.

He would probably just say “read the book”. It’s a common response.

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Over the long term, that’s complete isolation. You seem to be saying that the offspring of intermarriage never integrate into the population. That’s reproductive isolation by strong selection against hybrids.

As long as it’s only some, not all, what’s the problem? Again, you need effective reproductive isolation of populations.

Is there evidence of any such completely isolated populations?

Could happen, but how does this cause complete reproductuve isolation of any population?

…so as to result in complete reproductive isolation of some neighboring population. That’s your scenario. I don’t see it as plausible, and the paper you referenced doesn’t support any such thing.

That’s a strange reply considering that not all Africans who lived 4000 years ago have genealogical descendants today.

Link? @swamidass

I am saying some wouldn’t. For the ones that do, they could be someone else’s descendants besides A&E and vice versa.

That could end the presence of A&E descendants in that tribe. Its also possible there were no migration of other A&E descendants to that tribe, right?

Yes, but only for one or a few lineages.

I don’t know of any and I am not arguing for complete isolation but isolation from some lineages. We know some lineages of certain individuals went extinct in the past preventing them from having descendants today. Is it impossible for a person to have genealogical descendants in one part of modern Africa but not another?

The descendants of A&E that first come to Africa are wiped out by war or disease and there isn’t any subsequent inflow of other A&E descendants into Africa. This sounds implausible but its an answer to your question.

So you are saying genealogical lineages have gone extinct in the last 4000 years?

Can two mutually exclusive events both be likely? That seems unlikely.

Not parsing that one.

How can there be effective reproductive isolation for some lineage but not others in the same population? Remember that A&E’s descendants eventually become every member of the source population, as do the descendants of Fred & Wilma, the builders of Stonehenge, Nick & Nora, two folks in ancient Patagonia, and Franklin & Eleanor, a couple of peasants in Shang China.

In what way is there a mutual exclusion here?


25654-28254-1-PB.pdf (230.1 KB)

Yeah, if we assume A&E are among the “most” who have descendants today.