When Humans Faced Extinction

BBC ^ | 6-10-2003 | Dr David Whitehouse

[blam]

When humans faced extinction

By Dr David Whitehouse
BBC News Online science editor

Humans may have come close to extinction about 70,000 years ago, according to the latest genetic research.

From just a few, six billion sprang

The study suggests that at one point there may have been only 2,000 individuals alive as our species teetered on the brink.

This means that, for a while, humanity was in a perilous state, vulnerable to disease, environmental disasters and conflict. If any of these factors had turned against us, we would not be here.

The research also suggests that humans (Homo sapiens sapiens) made their first journey out of Africa as recently as 70,000 years ago.

Little diversity

Unlike our close genetic relatives - chimps - all humans have virtually identical DNA. In fact, one group of chimps can have more genetic diversity than all of the six billion humans alive today.

It is thought we spilt from a common ancestor with chimps 5-6 million years ago, more than enough time for substantial genetic differences to develop.

The absence of those differences suggests to some researchers that the human gene pool was reduced to a small size in the recent past, thereby wiping out genetic variation between current populations.

Evidence for that view is published in the American Journal of Human Genetics.

Oldest members

Because all humans have virtually identical DNA, geneticists look for subtle differences between populations.

One method involves looking at so-called microsatellites - short, repetitive segments of DNA that differ between populations.

These microsatellites have a high mutation, or error, rate as they are passed from generation to generation, making them a useful tool to study when two populations diverged.

Researchers from Stanford University, US, and the Russian Academy of Sciences compared 377 microsatellite markers in DNA collected from 52 regions around the world.

Analysis revealed a close genetic kinship between two hunter-gatherer populations in sub-Saharan Africa - the Mbuti pygmies of the Congo Basin and the Khosian bushmen of Botswana.

First migration

The researchers believe that they are "the oldest branch of modern humans studied here".

The data also reveals that the separation between the hunter-gatherer populations and farmers in Africa occurred between 70,000 and 140,000 years ago. Modern man's migration out of Africa would have occurred after this.

An earlier genetic study - involving the Y chromosomes of more than 1,000 men from 21 populations - concluded that the first human migration from Africa may have occurred about 66,000 years ago.

The small genetic diversity of modern humans indicates that at some stage during the last 100,000 years, the human population dwindled to a very low level.

It was out of this small population, with its consequent limited genetic diversity, that today's humans descended.

Small pool

Estimates of how small the human population became vary but 2,000 is the figure suggested in the latest research.

"This estimate does not preclude the presence of other populations of Homo sapiens sapiens (modern man) in Africa, although it suggests that they were probably isolated from each other genetically," they say.

The authors of the study believe that contemporary worldwide populations descended from one or very few of these populations.

If this is the case, humanity came very close to extinction.

[MattinNJ]

I don't believe the 'Out-Of-Africa' BS. I'm a 'multi-regionalist.

Ditto. I thought I was the only one.

[Ahban]

I thought Toba might be responsible too, but the more I think about it the less sense it makes. How come Toba did not restrict the genes of Chimps or anything else, just humans?

It is clear that Man is a very recent arrival, how recent is up for debate. They gave a 70-140K window, but that is based on a lot of assumptions about population size. It is also based on the idea that mutation rates have remained constant.

That is not a reliable assumption when you consider that the Vela Supernova bathed Earth in radiation at several times its current rate for thousands of years. That would mean the mutation rate in the past was higher than the current rate they are using to make those calculations. That might move the DNA appearance of man to the cultural appearance of man (40K).

[alloysteel]

And you have been comfortable all this time, in the belief that the rise of Homo sapiens sapiens was an inevitability of history. Still don't believe in Divine intervention?

Just wait until the next time human populations get culled back.

[ClearCase_guy]

I'm really not trying to turn this into a Creationist thread. Really.

But my view is that whenever some surprising dinosaur find is announced, one that stands evolution on it's head a little bit, the scientists say "Evolution is still valid. We have new evidence, and science knows how to deal with new evidence. We will tweak our theory of evolution and accomodate this new evidence." To me, they seem to jump through a lot of hoops in order to hold on to their precious theory of Evolution.

We recently had a thread (from a science journal) that cast some doubt on carbon dating. Maybe the world isn't as old as we thought. Now, this thread indicates that all humanity comes from a small group that lived some thousands of years ago.

Some people might be persuaded that the Creationist view, in which God had a hand in Man's existence, is being justified by recent findings.

Your mileage may vary. But I don't think standard Evolutionary Theory is being boosted by the stuff I see lately.

[Psalm 73]

"I second the earlier poster..."

I, too, "walk by faith and not by sight", but I'm afraid you're about to get flammed unmercifully for it.
(But be of good cheer, He has overcome the world !)

[Burkeman1]

Skin color and hair texture is largely a reflectin of climate. Caucasions and Asians have lighter skin due to UV radiation and the need to absorb more of it in Northern climes while Africans have dark skin in order to deflect excess UV radiation. Estimats range- but those who specialize in this area believe it took only about 20,000 years for dark skinned Africans who migrated to Europe to become "white". That is at least what I have read.

[MalcolmS]

In just a few hundred years, likely no more than a thousand, you can breed every variety of dog, from Chihuahua to Irish Wolf Hound, starting with some common mutts.

I would guess it would take about 16X longer for humans, given the likely age at onset of sexual maturity.

That would be if someone were directing the breeding program. A bit longer if left to themselves with geographic isolation, etc. as the diversity drivers.

[blam]

"I'm really not trying to turn this into a Creationist thread. Really."

Thank You. Please don't.

[dsc]

"Some people might be persuaded that the Creationist view, in which God had a hand in Man's existence, is being justified by recent findings."

Well, I happen to believe that God is entirely responsible for man's existence, but since I also believe that the Genesis creation story is allegorical, I don't know exactly how He went about it.

I've been thinking that God breathing life into Adam might be an allegory for God bestowing souls on vessels that he had created through a process that would leave the fossil record we find. My first thought on reading this was that perhaps those 2,000 were that group.

[Aric2000]

OK, so what you are saying is that it is hard to believe that it only took 70,000 years and a population of 2000 to get the diversity of the population we now have, but it's not hard to believe that it only took 6000 years and 8 people?

Does anyone else see something wrong with that logic?

Oh, that's right, goddidit, that explains EVERYTHING.

[AdmSmith]

Yes, and if you check the DNA of people from Eritrea/Ethiopia you can probably see that they went back to Africa after some time in "ME"/"Europe".

[I got the rope]

That is not a reliable assumption when you consider that the Vela Supernova bathed Earth in radiation at several times its current rate for thousands of years.

Bathed the earth with X-rays? Interesting. How much? Is there data or a educated guess on how much would have arrived here?

[blam]

"Estimates range- but those who specialize in this area believe it took only about 20,000 years for dark skinned Africans who migrated to Europe to become "white". That is at least what I have read."

Yup. Anthropologist Marvin Harris (RIP), thinks it could have been as recent as 10k years ago.

[CobaltBlue]

Remember, human beings self-select based on individual preferences.

Researchers testing preferences have overlapped multiple faces of many different races to come up with a "generic" human face, and then tested to see whether this face is more or less attractive than any given human face. Surprisingly, this "average" face is considered quite attractive.

Women are more attracted to "masculine" faces when ovulating.

Human beings are very interesting creatures.

[Tallguy]

Evolution can perform such wonders in such a short time-frame?

Some say yes. Evolutionary "bursts" can be followed by long periods when change is not noticeable. Frankly, it's all pretty tough to understand.

[Mamzelle]

re: It is thought we spilt from a common ancestor with chimps 5-6 million years ago)))

Where would junk science be without the passive voice to hide behind...

[blam]

"Women are more attracted to "masculine" faces when ovulating."

Yes, I read that...and attracted to less masculine at all other times.

[Aric2000]

Are you talking about ID, astrology, what Junk science do you mean?

[stuartcr]

I believe God created evolution.

[stuartcr]

And He did it in 70000 yrs, which biblically translates to 7 days and nites.....