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Humans Nearly Went Extinct 70,000 Years Ago
Josh Fink brings us a CNN story discussing evidence found by researchers which indicates that humans came close to extinction roughly 70,000 years ago. A similar study by Stanford scientists suggests that droughts reduced the population to as few as 2,000 humans, who were scattered in small, isolated groups. Quoting:
"'This study illustrates the extraordinary power of genetics to reveal insights into some of the key events in our species' history,' said Spencer Wells, National Geographic Society explorer in residence. 'Tiny bands of early humans, forced apart by harsh environmental conditions, coming back from the brink to reunite and populate the world. Truly an epic drama, written in our DNA.'"
we will actually reach that population level again.
Environmental damage here we come!
I guess only 2,000 survivors made down to the planet's surface from the Battlestar Galactica. They should have listened to Starbuck earlier.
This event probably ended up establishing the concept of "races", meaning small groups of geographically isolated humans ended up having a lot of genetically distinct features. As their populations grew, they seemed very foreign to each other and only in modern times those barriers to gene flow seem to be falling.
I look forward to the day when people stop saying "I'm X race" and instead say "I carry the genetic markers for A, B, and C." Well, perhaps it's unlikely, but an ex-biologist can dream, can't he?
I have a whopping 10 mod points, but would rather participate in this discussion instead, so here goes:
:P
I think that this is actually plausible. Things to mull over that could make this an interesting topic:
1) What evidence, 70000 years later, would decisively display the difference between a flood and a drought?
2) Could the Noah story be an allegory written after the fact to describe this event, with only the details mixed up? If so, what does that tell us about this story?
3) What remnants of an Ark would one expect to find 70000, or even 5000 years after the fact? Conversely, what evidence could be shown that would decisively PROVE OR DISPROVE that the event happened? And I'm talking about scientific evidence here. Not anecdotal faith-based cruft. Not even science-based faith-based cruft, if you please...
Love these topics. Go people, go!!
actually the whole almost dieing out thing just reeks of a total lack of intelligent design
Isn't 2000 people about the capacity of Golgafrinchan Ark Ship B?
Just saying...
Remain calm! All is well!
Actually the study can't support the statement that there were only 2,000 of us at that time. What it does say is that only 2,000 of us alive at that time managed to pass down their genes until today. There might have been a larger population whose genes we have lost in the intervening time (e.g. during the Bubonic plague).
The problem with these studies is that there isn't any DNA record of the humans that didn't make it. The only evidence we could hope to find of the humans that have died out is fossilized remains, which are few and far between.
120 characters isn't enough to explain it.
you mean 6000 years ago, and if by a drought you mean a flood, and if by 2000 human beings, you mean one bad-ass yachtsman named Noah and his hot wife Jessica Alba, then I would be inclined to agree. Otherwise I'm afraid this is just another godless article passed off as 'science' by Lucifer-worshipping scientists and their ilk over at CNN.
Conversation with government clerk filling out official forms...
Clerk: Full name please?
Me: Allen Dale Douglas
Clerk: Date of Birth?
Me: June 12th, 1981
Clerk: Place of birth?
Me: In a hospital.
Clerk: Which city and state, Einstein?
Me: Oh, Dallas TX, Presbyterian Hospital
Clerk: Sex?
Me: Sometimes.
Clerk: (rolls eyes ) Sex?
Me: Male.
Clerk: Race?
Me: Human.
Clerk: No, I mean what ethnicity are you?
Me: Texan.
Clerk: (rolls eyes again, tosses pencil up into the air and walks away)
And now we're an over-weight, not-too-bright, not-too-strong, disease-ridden, sorry-assed bunch of H. Sapiens.
What a difference 70,000 years makes!
"Have you ever thought about just turning off the TV, sitting down with your kids, and hitting them?"
Maybe it's because I pay attention to genetics and genealogy (and I thought people were geekier than I am here) but I clearly remember this news from 2006. Why is it getting recycled now, two years later?
The end of this article seems to cover that. Basically, this is a completely independent set of data (taken from the Genographic Project) that further confirms a theory that's been kicking around for a while.
This guy's the limit!
This whole article seems to rest on the premise that humans left Africa en masse about 60,000 years ago. This is likely, but still a hotly contested theory. A rival theory contends that modern humans (Homo sapiens sapiens) originated about the same time from Homo erectus, whose bones have been found in Asia and Africa (the multiregional theory).
It stands to reason that the tests on mitochondrial DNA of a group in Africa is only useful if you assume everyone left Africa sometime after 60,000 years ago.
Given there are numerous sites in Australia that claim to have artefacts stretching back at least that far (and possibly 176,000 years ago) it is very likely there were pockets of humans in other parts of the world much earlier than 60,000 years.
This research actually only shows that there is evidence of a population crash in Africa. Not that homo sapiens across the world had a population crash.
If the pattern goes 9am, 10am, 11am, why isn't noon 12am?
Floods typically do follow droughts.. so I wouldn't be surprised if an oral tradition was formed around how the global flood (which is a legend in most every culture) was passed on for 70,000 years or so.
How we know is more important than what we know.
2000 person orgy to save the species.
Engineering is the art of compromise.
This idea that we can prevent it, and then everything will be fine. Well there's two big problems with that:
1) What if even though we are the source, we can't stop it? What if it turns out there's just no way now to turn things around, we are too far down the road? What then?
2) Assuming historical extrapolations are right, the world has been much hotter and colder than it is now. Thus it is likely that will happen again. Thus no matter what we do, we are probably in for a big temperature change at some point.
So then if we assume it is true that a temperature shift of a few degrees will really screw us over, then we need to be preparing for it and figuring out how to deal with it. It really seems like a case of not if but when. Even if we are the cause and have the power to prevent this current change, a change that we can't will happen at some point. Also, just because we are the cause, doesn't mean we can prevent it.
Either way, the most sensible thing would seem to be to figure out what we need to do to be able to survive a temperature shift, not concern ourselves with what the cause is because unless we are extremely incorrect about past temperature, it is not a static function over any time period, and thus is not likely to remain so, regardless of what we do or don't do.
It bothers me that people keep talking about the hypothetical effects of global warming without any real data. CO2 levels have risen by 30%, and surface temperature have not shown enough of a trend that we can really say the temperature is even rising. Sure, there's less sea-ice than there was 30 years ago, but ocen levels have not risen.
Where's the beef? Why are people saying that we're going to see cataclysmic changes in our environment, when no appreciable changes have occured so far. What is the basis for all these predictions?
the explosion of the Toba volcano, in Indonesia, that was believed to take humans to the brink of extinction:
Across the world the last eruption of a super volcano was the Toba volcano in Indonesia. This erupted around 75,000 years ago spewing out tremendous quantities of rock and ash and is thought to have reduced global temperatures by up to 21 degrees centigrade.
Because the inheritance graph of humans is a DAG flowing backward in time (thus cannot create cycles), with each individual having exactly two parents. These research results estimate the number of unique nodes of this graph at a specified point in time by essentially tracing backwards from who is alive today.
People don't "intermingle", they have children. If the children die, or all the children's children die (or all the children's children's children die, ad inifinitum), then your unique genetic code is erased (except the portion of your genetic code that you shared with other individuals who got it through a different path in the graph).
In fact, it's slightly more complicated than that because when you have children you only pass on (an essentially random) half of your genetic code. You might have the dumb luck that none of the unique mutations in your code gets passed on to your children because they never land in your children's 50%. You therefore might have had a unique mutation that cannot ever be detected in the future genetic record because by chance you passed on the "common" portion of your DNA code and not the unique mutation.
So yes, branches of this DAG can and do die off. Nothing "points" to them, so they die. In fact, this is the very mechanism by which natural selection and speciation occurs.
The arguments they use in the article are statistical and even though they account for many factors, in the end they can only work on information available from surviving DNA.
120 characters isn't enough to explain it.
And I have to wonder if the author even read the original peer-reviewed article - which can be found at:
http://www.ajhg.org/AJHG/abstract/S0002-9297(08)00255-3
The actual study contrasts two complex hypotheses on early human populations in Africa. The major points are:
1. (Presented as the current consensus). Early humans lived in a one population in eastern or southern Africa. Around 90,000 years ago, this population splits. One of the daughter groups is the primary source of the Khoisan (a South African ethnic group with many "early" maternal lineages). The other is the source of the out-of-Africa migration 60-70,000 years ago. After the out-of-Africans leave, there is renewed migration between the two African groups.
2. (The new hypothesis proposed in this paper). Early humans split into two largely separate African groups starting around 150,000 years ago. Again, one of these is the primary source of the Khoisan and the other is the source of the out-of-Africans. Again, there is renewed migration between these groups after the out-of-Africans leave. (Also, this second hypothesis requires some limited migration from the Khoisan ancestors to the other group around 90,000 years ago to make the patterning of genetic variation work out).
The data which these hypotheses are trying to account for - in part - is that there is significantly more diversity in maternal lineages in Africa than out. In fact, all of the maternal lineages outside of Africa are a subset of *one* of the African lineages. So any explanation of this has to somehow derive a non-diverse population (the rest of the world) from a very diverse source population (Africans). Both of these hypotheses try to do this in fundamentally the same way (population splits in Africa), but the new paper argues that in order for the pattern to be as it is, a longer time of separation of populations in Africa is required.
There are no new population size estimates in the paper whatsoever. There is no discussion (other than an off-hand mention or two) of population sizes in the paper.
The CNN/Associated Press article is sensationalistic at best and misleading at worst.
And as an aside, whatever the "separate study by researchers at Stanford University" is - I couldn't figure out which one it was in the reference list - it is certainly about *effective* population size, which is _very_ different than census population size. For instance, the long-term effective population size of the entire human species is generally estimated to be around 10,000 *effective* individuals.
Precisely. The journalist who wrote this article does not understand the difference between population census (gross size) & effective population size. 70,000 years ago, the scope of genetic variation of humans - who have living descendants today - was contained in approximately 2,000 individuals. It's a more sophisticated idea, but it's also a far cry from the more sensationalist 'only 2,000 people survived'. To put this idea into a modern perspective, there are over 6,500,000,000 people alive on the planet today, but our species' effective population size is only about 10,000. If human populations 70,000 years ago had the same amount of diversity as we do today, then there were about 1,300,000,000 people alive 70,000 years ago. Obviously this is an absurdly high figure; we know from historic records that there were not more than a billion people alive as recently as 1800. What it does imply, however, is that our species, over the course of the last 70,000 years, has become more genetically homogeneous. This can only be explained by gene flow & natural selection. Recent work by Greg Cochran & John Hawks has shown that adaptive evolution has been accelerating rapidly over the last 40,000 years; our comparatively low Fst value (a measure of population differences) indicates gene flow between regions has also been increasing.
This study is based on Mitochondrial DNA, which is inherited through the female line. It's less than useful for determining the actual population, since the only population detectable through this technique is women who've not failed to have daughters. Note that my grandmother's mitochondrial DNA is going to be gone from the world after this generation, since she had only one daughter (plus two sons), that daughter had only two daughters (plus four sons), and those two daughters have only sons (two, last I counted). So, 60-odd descendents still living, but as far as this test is concerned, her entire family line is gone, or never was.
"I do not agree with what you say, but I will defend to the death your right to say it"
I have. I talked to a lot of them when I was getting my geology degree in college. You're right that the climate is constantly changing. You're wrong if you think that implies that humans cannot change the climate.
You're also wrong if you think that recorded human history is the only record of past climate that we can reference. There are numerous natural records of past climate that go back much further into the past. And by the way, the best estimate for an average global surface temp is actually about 14 degrees C, not 0. I have no idea where the grandparent got that number. Maybe they mistook temp anamoly for absolute temp.
Finally, it may surprise you to learn that many researchers of past and current climate do in fact hold geology degrees.
Build a man a fire, he's warm for one night. Set him on fire, and he's warm for the rest of his life.