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.

[ffusco]

Perhaps it's happenning now....

[Springman]

Bump fo later.

[ffusco]

All Science can do is observe behavior. Electrons and neutrons are attracted to each other. It can not explain why they do this, only the conditions where this is likely to happen.

It is plausable to state that God makes electrons and neutrons attract, but that is not in the realm of what is provable scientifically. As for me I don't think God is a micromanager, his rules as observed by physics thus far are inviolate.The Newtonian God view seems to fit the available data.

[PatrickHenry]

Electrons and neutrons are attracted to each other.

I think you meant to say electrons and protons.

[blam]

"There's an alternate theory that allergies are the result of our environment being too clean. "

Yup. I've read some of those stories. Seems a child will aquire the majority of their immunity before they're six years old. It has even been suggested that kids that play in the dirt and are raised around a lot of animals are healthier, overall.(...and that must occur before the age of six)

[CobaltBlue]

I read about it in something like Time or Discover, but a quick google search using as search terms

overlapping photos faces attraction

turned up this link which has links to other studies.
http://jrscience.wcp.muohio.edu/nsfall02/labpacketArticles/draft2-whataretherulesofa.html

[Pharmboy]

Well, the Black Death wasn't exactly a walk in the park. Genetic bottlenecks were major drivers in evolution, for whatever reasons...

[CobaltBlue]

>>My first thought on reading this was that perhaps those 2,000 were that group.<<

Fascinating concept, which would make a great fantasy, folk tale, or maybe even science fiction story.

[CobaltBlue]

>>I believe God created evolution.<<

Me, too. I have no idea what the percentages are, but there are a lot of us.

[Skywalk]

Doesn't the multi-regional theory still have an "out of africa" element? That several races could develop nearly simultaneously and yet all be capable of producing fertile offspring is an impossibility.

However, native members of precursor humans could have mixed with homo sapiens to produce homo sapiens sapiens.

[CobaltBlue]

>>It all boils down to what one wishes to believe.<<

Ah, ah, ah! Cheating! You can't pick the part you like (small pool of original Homo Sapiens Sapiens) and ignore the rest (exactly WHY the genetic evidence points to a small pool of original Homo Sapiens Sapiens).

Tsk, tsk.

[blam]

"Well, the Black Death wasn't exactly a walk in the park. "

Yup. And that was not the only one either. Apparently they went on and on and...

In fact, here is one example in my hometown.

Church Street Graveyard

[wafflehouse]

see tagline:

[PatrickHenry]

PLACEMARKER

[CobaltBlue]

>>"It is thought that we split off from chimps 5-6- or eight hundred million years ago..." used to disguise a no-fact fact. It is thought-- By whom? Sez who?<<

I don't concede that your f'rinstance is a real example, but let's agree to discuss matters in a broad and general manner.

I don't agree - for a second - for a nanosecond - that a heavy-duty research study reported in a peer-reviewed journal has ANY hands waving. On the contrary, they are so dense with footnotes as to be almost indigestible.

Which leads me to suspect that everything you know about the subject you learned in a college survey lecture class, where it's sort of not expected for the professor to provide footnotes during his lecture, and, indeed, more likely than not that your lecturer was a grad student or associate prof who doesn't know very much, or maybe you learned it on TV.

I studied anthropology undergrad and worked as a research assistant to the head of the department, and, sister, if you tried that "hands wavink" bullony on my former boss, he'd blow you out of the water.

[blam]

"see tagline:"

It's true.

[CobaltBlue]

I became interested in graveyards myself recently due to my interest in native plants. They are storeyards of native plants, many of which are extinct or rare anymore.

There are a lot of reasons to be interested in graveyards - architecture, folklore, geneaology, you name it. Things go in and never come out.

[blam]

"I became interested in graveyards myself recently due to my interest in native plants. They are storeyards of native plants, many of which are extinct or rare anymore."

I've read that, specifically roses. There's a company, Heirloom Plants, I think, that sells seeds to old varieties of food plants. (I can't get a good tomato anymore)

[CobaltBlue]

>>I can't get a good tomato anymore<<

Dunno if you can grow them down in 'Bama, but Brandywines are superb. Red Brandywines, the pink ones and the black ones aren't as good. They do great in Northern Virginia.

In New Orleans, I used to grow Creoles.

[blam]

"Dunno if you can grow them down in 'Bama, but Brandywines are superb. Red Brandywines, the pink ones and the black ones aren't as good. "

Probably not. I never heard of them. I don't know what kind my mom used to grow, they were as big as Beefeaters but, they weren't Beefeaters.