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.

[js1138]

That's before they learn to drink like a Gator.

[blam]

"An interesting counter to this can be found in the special edition of Scientific American on human evolution -- Alan G. Thome and Milford H. Wolpoff "The Multiregional Evolution of Humans". "

Yup. Wolpoff is my guy. He resembles a Neanderthal. lol.

[js1138]

Another way you can tell real science from junk is the way the scientist qualifies his assertions.

Real scientists qualify their assertions. Science writers for Time Magazine and PBS might not.

We just had one of these threads pulled because one poster insisted on posting quote fragments expressing qualification, truncated in a way that implied the opposite of what the scientist believed. So if a scientist expresses himself carefully, his words are shredded and reprocessed to use against him. Just an observation, but I found about a dozen web sites devoted entirely to this process, usually having such headlines as "Scientists speak out against evolution."

[blam]

"This is the first time I have seen the mention that the human race was so close to extinction aside from your own posts. "

It's important to pay attention. Actually it's been around for a while. ...and, I wouldn't count the Chinese out yet, we may in fact be 'Out Of China.'

[Burkeman1]

So...we're having births of stronger humans daily

I don't think so. You are forgetting modern medical science. The infant mortality rate in the 1st world is a fraction of what it used to be only 100 years ago. I have an older brother who is afflicted with allergies of all types and was a sickly baby. We joke with him that if he had been born in 1900 he would never have lived past 5 years old and that is probably the truth. In any case we have far more humans that would have died in childhood but who are alive and passing on their genes to other generations. I think the result is that we have "less strong" genes overall than we did just 100 years ago.

[PatrickHenry]

But if it can't be reproduced, it's not science. If there's no doubleblind, it's not science.

Astronomy therefore is not science, by your personal definition. Nor is geology. Nor climatology. I believe your definition is limited only to the so-called "experimental sciences," which are not the only sciences.

[js1138]

I have an older brother who is afflicted with allergies of all types and was a sickly baby.

There's an alternate theory that allergies are the result of our environment being too clean. The trick that wisdom teaches us is to take all new pronouncements with a few grains of salt. Be particularly wary of the way statistical studies are presented. If, for example, a condition affects one person in a thousand, then a hundred percent increase will mean that two people in a thousand are affected. Most medical studies are more exaggerated than this example.

[Mamzelle]

But you *can* reproduce a study in astronomy, geo, climatology...and you can speak confidently about the results of those studies. But the conclusions that are drawn bear little relationship to what the studies can demonstrate. There are only murky clues and plausible theories, to be shot down by the next murky clue or slightly more plausible theory. All you're left with, really, is the faith these scientists have in themselves--and knowing the egos and corruptibility of scientists, I'll pick a better faith. These erstwhile scientists write as if working with far better evidence than they actually have--as if from the kind of experimental data that a pharmacologist works from.

[Centurion2000]

bump

[Ahban]

Would it be enough time? Sure. Let's say man appears 40K ago. Mutation rates from 40-11K ago are about the same as today. From 11-7K ago they average 10 times the current rate due to the Vela Supernova(see below). So for more than 1/10th of our existence cosic radiation was ten times its current rate. If this caused mutations in a linear fashion, as the mouse study you linked to suggested, then this implies that the "apparent DNA" age of man is about twice his actual age. Not 80K, but 40K, same time as the artifacts show up.

I found this from the reasons.org site...
paper entitled "Terrestrial Paleoenvironmental Effects of a Late Quaternary-Age Supernova" was published by geophysicist G. Robert Brakenridge in the journal Icarus (v. 46, pp. 81-93). Dr. Brakenridge describes measurements that date the Vela supernova as having occurred sometime between 9300 and 6400 B. C. (A supernova is the cataclysmic explosion of a massive star; this one is called the irela supernova because it occurred in the Vela constellation.) These dates fit well with the Biblical date for the Genesis Flood.

Dr. Brakenridge also points out that this supernova occurred about three times closer to Earth than any other supernova event in human history. Thus, it is probably responsible for most of the cosmic rays that now come our way, cosmic rays which break down protein. Further, the Vela supernova would have affected the upper atmosphere in such a way as to bring about a global cooling and would have damaged the ozone layer so t:, as to increase ultraviolet by two to ten times. Dr. Brakenridge documents geological evidence for both effects in the era between 8,000 and 9,000 B. C., also the time of the disappearance of some diatom and plankton species.

[Aric2000]

What they are doing here is putting out a scientific hypothesis, their study has drawn them to this possible conclusion.

They have put their hypothesis out into the public light in order to be peer reviewed.

This hypothesis is NOT set in stone, but they will catch the interest of other scientists who will try to falsify it, or the other scientists will come to the same conclusion, and verify the findings.

It is fun to discuss these different hypothesis, but do not mistake those of us who discuss it as adherents to this particular hypothesis, it is fascinating to discuss the implications and what they might mean.

I think that you are making the mistake of assuming that since it is out there for public consumption that these scientists are somehow claiming that it is fact, when in fact, they are not.

[Dementon]

Researchers testing preferences have overlapped multiple faces of many different races to come up with a "generic" human face...

I was actually looking for some information on that study just last week.

Would you happen to have a link?

[LittleJoe]

Just wait until the next time human populations get culled back

Interesting thought. These time frames do suggest that mankind suffers cataclysmic reductions periodically.

I wonder when the next one will happen...

[Mamzelle]

re: I think that you are making the mistake of assuming that since it is out there for public consumption that these scientists are somehow claiming that it is fact, when in fact, they are not. )))

Could be. Not that the assertion does not intrigue--it does. But you don't have to read very far to encounter that old passive voice sentence structure--"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?

So what you have is an entertaining theory--but there ought to be more skepticism written in to be called science.

[LittleJoe]

To me, they seem to jump through a lot of hoops in order to hold on to their precious theory of Evolution

Both sides seem to be guilty of this. I, on the other hand, see no conflict between evolution and creation.

[Aric2000]

This is a BBC article, not a science journal.

But the fact is that it is indeed thought that we split off from our common ancestor about 5-6 million years ago. The chimps went one way and we went another.

There is evidence to support this assertion, fossils, DNA etc, but you will notice again, that is says, "it is thought" again, an assertion, but NOT stated as fact.

You seem to think that science states facts, or PROVES something. It does not, science gives evidence and explanations or theories to explain that evidence.

They are just stating their hypothesis, nothing more, it is up to other scientists to have the built in skepticism to weed out what may be true or what may be false within the hypothesis.

It is not up to the scientists that created the hypothesis to write in the skepticism, It is for other scientists to peer review it and be skeptical.

Be as skeptical as you want, but to say that "it is thought" somehow states a fact, well, that's pretty misleading as well.

[ClearCase_guy]

I can embrace both evolution and creationism. But to do so I say "There is a God who performs actions on Earth. And there is Science which performs actions on Earth." I don't really have to jump through too many hoops -- because I believe that God can do anything.

Many scientists are only willing to say, "It is Science which performs actions on Earth." They jump through hoops because they do not, under any circumstances, want to acknowledge that God can perform actions on Earth.

Seems to me that whenever these scientists come up against something that they cannot explain, or which flies in the face of what they have postulated, their starting position is: "Okay, the one thing we know for sure is that God had nothing to do with this. Now, how are we going to come up with a theory that proves that?"

They've got an agenda. I also have agenda. But I admit mine. They'll tell you that they are objective.

[Mamzelle]

The passive voice performs well for those who seek to gloss over a rough patch in the exposition. "It is thought", read quickly, works like "It is established." The 5-6 million (why not ten, fifteen, twenty? One number is as hard to disprove as another) may not be all that "established", but you need some foundation to get started on the next fun theory (and the next grant application).

Pick up some science writing and look for the passive voice--it's there to distract. You won't find much of it when someone's life is on the line, where a dangerous mistake will become quickly obvious. Scientists who deal in the origins of things don't fear such awful accountability. "It is thought that this drug won't kill you..."

[AdmSmith]

If we assume that the mutation rate is more or less constant this would imply that the population with the largest variation is the oldest.

A strong indication that we originate from Africa is that the variation of mitochondrial DNA is very large among Africans, and smaller among other groups.

[ffusco]

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

Interesting. I remember reading that farmers have more resistance to germs because they have built up a tolerance, in fact didn't Dr. Jennerf observe that milk maids had some immunity to small pox and used this to develop the vaccine (from the latin Vacca for cow) which was a weakened vaccinia virus?