How large was the group of humans that we've descended from?

[BlackDog]

We had a "chokepoint", with the humans down to maybe 5,000. One of the lines in that population was very success, and this is where "Mitochondrial Eve" comes from, everybody seems to gotten some of her genes. However, I'm betting there are still some isolated populations out there that are untested and may not be related to her at all.

From several recent sources I've seen: population <10 000, or something like a couple of thousand women of reproducing age. The BBC doc linked to in this thread is excellent. The clickable educational thing at Bradshaw Foundation is also very good:
http://www.bradshawfoundation.com/journey/

Population that size, trading people among various groups to keep the breed healthy (although they probably had their own reasons for doing it), and it's not surprising one woman shows up in the modern gene pool. 20 generations would do it, I think. Me no do maffs.

Where is your avatar from?

[Fact-Man]

There would have been a fair sized population of hominids with varying traits. At some point, geographical isolation would have meant that one sub-group would have evolved into the ancestors of modern-day Homo sapiens.

Identifying the point at which a new species arises is impossible. There is a continuous gradation from the ancestor species to the descendant. It is the breeding isolation (usually geographical) of one group from other similar groups that causes speciation.

Indeed and we've already identified several different species that emerged in Africa in what were undoubtedly regionally isolated groupings of hominids that existed over long periods of time, and it seems we keep finding new ones (many paleo hominid fossils are difficult to identify with one species or another).

So it seems we'll never know what a "starting population" was because the beginning occurred over time and happened in a variety of different regions, a situation of high but very slow flux. There may have been as many as 50 precursor species. The situation doesn't gain much clarity until homo erectus made his way out of Africa through the Middle East and into Europe and Asia and beyond. Even as late as about 20,000 years ago there were still two species living on the planet, Neandertal and Homo Sapiens.

It is a fascinating question but the history spans several million years and is marked by differentiated speciation in widely disparate regions ... until it becomes impossble to have the kind of clarity we'd like. Obviously, the picture will gain more focus as time passes and new finds are made, but to hope for ultimate clarity is probably not reasonable because we won't find enough to complete the picture in any comprehensive way.

Given the time and geography involved we're probably fortunate to know what we do know about it, which is as far from zero as it is far from complete. We can hope that more finds will occur to help fill in the picture and surely they will be made, but I don't think we'll ever have a fully developed notion of our origins. We will have some good general ideas, but a definitive map seems out of the question.

[Gawdzilla Sama]

We had a "chokepoint", with the humans down to maybe 5,000. One of the lines in that population was very success, and this is where "Mitochondrial Eve" comes from, everybody seems to gotten some of her genes. However, I'm betting there are still some isolated populations out there that are untested and may not be related to her at all.

From several recent sources I've seen: population <10 000, or something like a couple of thousand women of reproducing age. The BBC doc linked to in this thread is excellent. The clickable educational thing at Bradshaw Foundation is also very good:
http://www.bradshawfoundation.com/journey/

Population that size, trading people among various groups to keep the breed healthy (although they probably had their own reasons for doing it), and it's not surprising one woman shows up in the modern gene pool. 20 generations would do it, I think. Me no do maffs.

Where is your avatar from?

Arte Johnson, "Laugh In".

"Verrry interesting!"

[GenesForLife]

Hey Susu, good to see you here

[llanitedave]

AFAIK tens of thousands.

We have probably at times gone down to very low numbers indeed.

We are all seriously incestuous.

http://en.wikipedia.org/wiki/Toba_catastrophe_theory

There are some major problems with the Toba hypothesis, IMO.

The idea that the eruption would have caused a catastrophic global population collapse except for some relict population in Africa is contradicted by the evidence mentioned in the article linked to, including the survival of Homo floresiensis on Flores, and indications of survival on the Indian subcontinent. Thee's more, though that the article doesn't mention. If humans in Africa were decimated in population, then the animals they shared there environment with would have been expected to have undergone a similar genetic bottleneck. Yet there is no such bottleneck recorded for zebras, lions, gorillas, chimpanzees, antelope, elephants, or any African species with the exception of the cheetah. And the cheetah's bottleneck was far more severe and more recent than what might be attributed to Toba.

There are other ways for a population bottleneck to be recorded by the genes, one is a rapid expansion of one small subgroup that outcompetes and outbreeds all others while migrating outward. That has problems because it requires a lack of interbreeding between the expanding population and extent populations in new areas, but there may be other explanations as well. The Toba bottleneck, however, just seems to leave too many gaping gaps in its explanations.

[Woodbutcher]

In my case it was just Mommy and Daddy.....

[Theophilus]

A population bottleneck of two is certainly a possibility. Many genetic studies are done that way, so that F1, F2, F3....etc can be examined. Significant phenotypic variation is usually seen even by F2.

But on the other hand, the population bottleneck group could be larger. We don't fully understand how speciation occurs, but it is unlikely to develop unless there is near complete isolation of a smallish population group.

[Gawdzilla Sama]

In my case it was just Mommy and Daddy.....

William Tenn's "The Seven Sexes" comes to mind for some damn reason.