As I understand, our species originated in Africa and migrated out. Do we know for sure if present day Adricans evolve from the folks who stayed behind or if some of the original migrants went back ?
Apparently there is now DNA evidence to support the theory that humanity migrated out of Africa rather than in, but I don’t have sufficient knowledge and comprehension to explain it really well.
The DNA evidence is that there is more diversity amongst Africans. That indicates that non-Africans descended from smaller populations presumably smaller populations that migrated out of African. I don’t see how that would indicate that there was not migration back in. Almost certainly there was at least some.
Just a few days ago, a Doper linked to a study deducing migrations into North Africa.
The distribution of R1b Y-chromosome, which originated in Central Asia, shows a high concentration in Northern Cameroon. (Why did this haplogroup not spread during the Bantu expansion? Just the separation between northern and southern Cameroon? I don’t know if researchers have put a date on the arrival of R1b in Cameroon.)
Well, it’s not like Cro-Magnon (or earlier) said “hey, I outta here and heading for Thailand beaches for a vacation!” People obviously milled around, each year exploring a little further and finding more relatively untouched happy hunting grounds a few miles further on. Some settled, some kept moving.
From the distribution of DNA of established ancient populations, you can get a rough idea when two groups separated. The different populations of Africa have very much more differentiated DNA than the rest of the world’s populations, indicating they have been split up from each other longer (I.e. earlier common ancestors). North American Indians, for example, appear to have migrated from western Siberia eastward starting 20,000 or more years ago - based on DNA.
There is no evidence hat a group of African population is more closely related to, say, India subcontinent than to others around them in Africa. If a group got to Iran, let’s say, and some turned around and went back, then you’d expect them to be more related to Iranians than to neighboring tribes. There isn’t this sort of finding.
Plus, consider that the original hunter-gatherer expansion was to find easy food. Many of the ideal sites are nice river valleys, separated by mountains, deserts, and other rough terrain. On the way out, they passed this as untouched wilderness, probably with a passable food supply. By turning around and going back, they’d have to fight past or defeat other tribes that had already scoured the wilderness and eaten all the easy pickings.
Typically, groups that overrun others have an advantage - bigger brain, the bow, the metal sword, the iron sword, horses, fast large ships… Most of these came much later in the stage of civilization.
Based on DNA, the first wave was about 70,000 years ago; at that time, most modern humans are descended from a very small population - maybe a few hundred individuals.
The genetic makeup of most sub-saharan africans is from “folks who stayed behind” with major exceptions in the Sahel and east africa where there has been more mixing in modern times–and of course isolated exceptions elsewhere.
The migration wasn’t “one way.” There was some back diffusion of genes as the geographic gates opened and as mankind became more mobile.
There was one main migration out of africa about 80kya, though. (There may have been an earlier one that didn’t end up populating the non-african world).
Generally speaking, ancestral populations are tracked paternally through Y chromosome analysis and maternally through mitochondrial DNA, which is mostly passed through the mother for obvious reasons.
Y Chromosome analysis and mtDNA analysis gives us a broad idea of gene spread, and this in turn gives us a general idea of how anatomically modern humans spread out of africa. Because DNA changes over time, and because those changes can be presumed to be reasonably regular, we can track different Y and mtDNA haplogroups.
Here’s a pretty cool graphic showing one construct. Notice at the end as the Sahara gate opens there is some back diffusion into the Sahel from northern africa, for example.
And of course in the last few thousand years, quite a bit more gene flow here and there once humankind gets more mobile.
Unrepresented in this graphic ( as far as I know) is the putative introgression of both neandertal and denisovan genes into some of the eurasian lines from more ancient hominid lineages who had made it to eurasia (presumably) hundreds of thousands of years earlier.
Consider reading Oppenheimer’s Out of Eden if you want a nice lay book on the topic.
Of course, the link is by no means settled and agreed-upon data. The DNA evidence there suggests humans settled Australia by 65,000 years ago, and North America by 20,000 or so years ago. Most modern archeology suggests 45,000 and 14,000 roughly for the dates. There is not a lot of physical evidence either way. The questionable thing, for example, is that humans would make it to Chicago or New York by 19,000BC then in the face of advancing glaciers, they would remain a tiny isolated group. They would not move south into warmer climates and expand to fill the continent(s) for 5,000 years, then suddenly go forth and multiply. That seems very odd given the rate of expansion before and after.
It’s not just North Africa - it’s figured that there was prehistoric bidirectional migration in the Horn of Africa as well.
Post-agricultural, there’s stuff like the Jew-descended Lemba in Southern Africa, or the presence of Eurasian markers even in the Khoi-San - clearly, there was always two-way flow, but the reverse direction just was never as strong as the OoA flow, until stability was achieved sometime around 1000 BCE to make it stand out more.
Point is, there’s been just as much Völkerwanderung in Africa as anywhere else, it’s just not as well-attested - not as much archaeology done, less preservation in tropical climes, most of it pre-literate.
Even if the contact points between Africa and Eurasia are few, any admixture there is going to disperse over the rest of the continent in a few centuries.
Africa was never genetically isolated. I think there just hasn’t been enough actual genetic sampling done in Africa to even begin to get the full picture, but that’ll come.
Groups always move around. The Horn of Africa being one of the obvious migration points, no surprise there’s mixing there. Yes, there’s some mixing everywhere. If you allow a few miles a year migration, it takes less than 1,000 years for humans to spread across the world, so it’s not as if any group headed out (or back) at a break-neck pace.
Generally, though, one group of humans do not push another off their home turf without some advantage. If it’s nomads arriving into a settled valley from a more sparse wilderness, that won’t likely be numbers. Generally it’s a technological edge (fire, animal domestication, boats, bow and arrow, etc.) or an edge in weapons, although it could be a social one - like more cooperation between villages (a proto-empire?). Natural barriers made migrations more difficult, i.e. the Sahara effectively isolating southern Africa from the outside except for the route along the coast and Nile.
So assimilative flow is not unusual - many cultures traded women, adopted orphans from outside the group, etc. Another reason for a large influx of invaders might be food disappearing from their original habitat - volcanos, climate change, etc. Then a massive number of invaders might overwhelm an otherwise prepared defender population - but again, physical barriers would reduce the flow of invaders. 10,000 hunter-gatherers paddling along the Red Sea coast would likely be decimated by starvation before they reached Somalia.
I’ve heard of this too, and it’s quite interesting. The R1b Y-chromosome haplogroup is strongly associated with Romance and Celtic language speakers, and, to a lesser extent, with Germanic (e.g. English, German, Swedish, etc.) language speakers. R1b is extremely common in France, Spain, and Ireland, in some parts over 90% of men have this.
So what happened? Did the R1b population of Cameroon come from disgruntled Highlanders who got sick of the dreary Scottish weather and decided to GTFO of Europe, or do they descend from an ancient population of R1b that had not yet left Africa? I don’t think it’s clear, but its possible that it could have happened.
R1b originated (separated from R1a) about 26000 years ago in West or Central Asia. The split into R1b1a and R1b1c occurred a few thousand years later. R1b1c is the clade associated with Chadic languages and Cameroon. Essentially all West European R1b is in one specific subclade of R1b1a, i.e. R-L11 = R1b1a2a1a.
The Northern cameroun is very ethnically different than the southern Cameroun and is also different climate and ecology. It is not the zone of the bantu origin.
Of course, some of the migrants went back. I met many people in Africa who were born in Europe or America, and many more born in Asia. The entire population of Liberia is comprised of people who returned from America, many of them of partly European ancestry…
And this even happens completely outside of Africa. Many Americans who are descended from British colonists who settled in America in the 1600’s move to the UK today. It’s probably even more common for people whose ancestors moved to America more recently and have an immediate claim to citizenship, as opposed to needing to go though the visa application process.
Thank you. So it was coincidence that the source of the Bantu expansion, and the genetic Chadic-speaking center of some ancient conquerors from Asia, are both located in what is arbitrarily the “Cameroun” state today.
I only know about the R1b1c Chadic-speakers becuase I read about R1b (my own haplogroup). Is there any archaeological understanding of these Chadic/R1b1c people?
Fascinating. Northern Cameroonian ethnic groups assign themselves all kinds of fantastic origin stories- Egypt being the big one. I do recall some claiming to have origins from the Mediterranean coast.
Cameroon is a stunningly diverse place.
Not the entire population, no. Mainly the Americo-Liberians.
There has been a major divide and a great deal of hostility over the years between the Americos and the other Liberians.