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Earth Science

Humans Nearly Went Extinct 70,000 Years Ago 777

Posted by Soulskill
from the come-from-behind-victory dept.
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.'"
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Humans Nearly Went Extinct 70,000 Years Ago

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  • by clonan (64380) on Thursday April 24, 2008 @06:19PM (#23190706)
    we will actually reach that population level again.

    Environmental damage here we come!
    • by shbazjinkens (776313) on Thursday April 24, 2008 @06:22PM (#23190754)

      we will actually reach that population level again. Environmental damage here we come!
      Hear that Kelly Kapowski? Not if I was the last man on Earth, eh?
    • we will actually reach that population level again. Environmental damage here we come!

      I knew someone would say this. Alright, I'll bite. Name one plausible environmental damage scenario (other than full-out nuclear war) that would cause a significant proportion of human extinction.

      The most extreme predictions of global warming will hardly slow down human population growth, much less actually reduce populations, much less threaten us with extinction. (Of course, predictions are that human population growth will naturally slow and even stop over the next 50 years, but that's another subject).

    • by brunokummel (664267) on Thursday April 24, 2008 @07:46PM (#23191940) Journal
      Mother nature must have said:
      "Darn it, that was close, I'll get them next time!"
  • by Dzimas (547818) on Thursday April 24, 2008 @06:25PM (#23190820)
    I guess only 2,000 survivors made down to the planet's surface from the Battlestar Galactica. They should have listened to Starbuck earlier.
  • The concept of races (Score:5, Interesting)

    by PIPBoy3000 (619296) on Thursday April 24, 2008 @06:31PM (#23190878)
    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?
    • by Kelz (611260) on Thursday April 24, 2008 @06:34PM (#23190930)
      Or perhaps instead of saying "I'm X race" just say "This is my speciality and these are my accomplishments!" Once you get to a certain average prosperity level worldwide, it eventually stops mattering.
      • Re: (Score:3, Insightful)

        by thomasw_lrd (1203850)
        Now that's the best concept I've ever heard on slashdot. Makes the internet really nice. Nobody knows what race you are, or education, or even sex. And none of it really matters in the end.
        • Re: (Score:3, Informative)

          by Hatta (162192)
          Well if you're on the internet, chances are you're not black, you are literate, and are male. Though I suppose some illiterate black lady is going to post to prove me wrong now.
    • by Digi-John (692918) on Thursday April 24, 2008 @06:38PM (#23191004) Journal
      Speaking as an American, as long as dumbasses think they're special because some of their ancestors came from Ireland 8 generations ago before proceeding to mix with every other background in the US, we're going to hear a lot more "I'm Irish" or worse "I'm 1/16 Cherokee, 1/2 Irish, 2/7 Italian..." crap.
      • by Anonymous Coward on Thursday April 24, 2008 @06:57PM (#23191258)
        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)
      • by lottameez (816335) on Thursday April 24, 2008 @07:37PM (#23191826)
        I would agree with you were it not for my Scottish stubbornness.
    • by jd (1658) <imipak&yahoo,com> on Thursday April 24, 2008 @06:53PM (#23191210) Homepage Journal
      Oh, it would have taken more than one such event, but we know that more than one such event occured. There have been other reports of other droughts nearly killing off humanity and the bottlenecks showing up in the DNA. Once humanity fragmented globally, however, mutations would have stayed reasonably local, and this also created races. (The two African tribes mentioned in the article formed from the drought mentioned and the Australian aborigines formed from early geographic isolation, making the three very special examples of humanity, but that should not lead anyone to conclude they should be treated as ouside humanity - they've a greater right to the title than most extremists.)

      The rest of humanity spread out across the globe, the Genography project has some nice maps of how the genetic markers show humanity to have moved. They do make one error when it comes to Europe. Europe was settled at least twice - once by a long-headed hunter-gatherer people and then later by a rounder-headed farming people. The long-headed people are the ones who developed lactose tolerence and anyone who can digest cheese or milk in any quantity is descended from the long-heads. In order for that to make sense, the long-heads must have migrated with cattle or goats, much as many nomadic tribes do today. The Iron age "Ice Man" (central Europeans give them such boring names - at least Britain's bogman was called Pete Marsh) was, if I remember the description correctly, one of the round-headed people. He was also left-handed, but that probably doesn't signify anything of interest. He was either a trader or a trapper and there can't have been many tools in either trade that were designed with a specific hand in mind.

      • by flyingsquid (813711) on Thursday April 24, 2008 @07:21PM (#23191622)
        I'm not entirely sure that I buy the reasoning behind their claims. OK, let's assume that they're right that all modern humans descend from a very small population, of about 2,000 people. It does not follow that the entire global population of H. sapiens was, at some time, 2,000 people. Perhaps there were 200,000 total, but only 1% of the people developed sophisticated technologies and cultures which allowed them to expand, eventually wiping out the remaining 99%. You still have a bottleneck, but your total population never goes below 200,000. For example, if the Neanderthals are considered a subspecies of H. sapiens, then you could have had 198,000 Homo sapiens neanderthalensis, and slowly that 1% of the species which is Homo sapiens sapiens expands and wipes them out. Certain populations of the species may have gone through bottlenecks, but the species as a whole has a stable population. Did that happen? I don't know, but you'd have to address this possibility before you go around waving your arms about the species being on the brink of extinction.

        Also, keep in mind that the genetic evidence is just one line of evidence, and that's it's difficult to interpret. If their conclusions are correct, then other lines of evidence should corroborate their story. In particular, if humans nearly went extinct 70,000 years ago, then shouldn't we expect to see that in the archeological evidence, with stone tools becoming less common for a period?

        • by jd (1658) <imipak&yahoo,com> on Thursday April 24, 2008 @08:19PM (#23192262) Homepage Journal
          You are correct to be suspicious. The other event I mentioned was much stronger - there was a definite genetic bottleneck, there was a geologically determinable drought, there was a reduction in human activity, and humans were still more-or-less in one region and thus much more likely to be affected by a drought. Numbers can be calculated directly from evidence of remains, but also by looking at what would have existed in the way of food and water, then calculating the maximum supportable population. You can do that with a single cluster.

          This newer claim must be treated with caution, because it involves humans that have spread out (less likely to find remains, less likely the humans would have been affected catastrophically) and it's much harder to calculate numbers, because it's much harder to determine what would have been available to whom and what level of trade would have existed when levels of critical resources differed between human-inhabited areas.

          DNA is also a dangerous thing to go by. We know there was a mitochondrial Eve, and we know a date but not whether it was the date of the event horizon (the point at which all surviving humans were descendents of Eve, within a timeframe in which differences in mtDNA would not yet be significant in the only regions we have really mapped for such purposes) or the point of singularity itself (when Eve lived). We also don't know why homogenious mtDNA occured - unless it conveyed such dramatic advantage as to be always selected (mtDNA handles energy conversion in cells), there's nothing that makes it obviously preferential, so all mtDNA lines should have survived on a completely random distribution.

          Only twelve descendent lines exist in the whole of Europe and Asia. Another eight pretty much covers the rest of the planet. I say "only", but remember at least one actual catastrophic drought and this supposed one happened much later than mtDNA Eve. If a uniform, homogenous strain was preferential, we should not be getting such divergence now. It's not a simple picture.

          (Also, dating an event by mutations is dangerous, since mutations can revert, not all markers mutate at the same rate, and all kinds of other factors make such calculations extremely messy. On the DNA mailing list, people often point out that the margins of error on last common ancestor calculations are so broad as to make the calculation worthless.)

          It's a Douglas Adams kind of situation: even if we knew for certain, we wouldn't really know what it was we were certain about, or indeed that we were even certain about it.

  • by dtjohnson (102237) on Thursday April 24, 2008 @06:34PM (#23190926)
    Going back 70,000 years, then, there were only 2,000 of us...and...let's be honest...we were probably a skinny, not-too-bright, not-too-strong, disease-ridden, sorry-assed bunch of H. Sapiens. The Neanderthals obviously outnumbered us by many times over and could have rid the world of our kind. Thank you Neanderthals for sparing us...and we're sorry about anything we might have done to you...later.
    • by diablovision (83618) on Thursday April 24, 2008 @06:52PM (#23191186)
      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.

      • by HomoErectusDied4U (1042552) on Thursday April 24, 2008 @09:24PM (#23192818)
        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.
    • Re: (Score:3, Interesting)

      by Chris Burke (6130)
      Maybe. Don't sell your species short. We're a clever, sneaky, and potentially quite vicious bunch of apes. These few remaining humans, even if they got lucky (as they almost certainly did), demonstrated that they could survive when nearly all others of their species died. Whatever their physical fitness level, they probably had what it took upstairs.

      Of course what I'm really saying is that in all probability we would have struck first, catching the Neanderthals by surprise. And without any concept of a
      • Re: (Score:3, Interesting)

        by Shakrai (717556) *

        Whatever their physical fitness level, they probably had what it took upstairs.

        That's pretty much the only reason we have survived. Physical fitness is helpful but let's face it -- even the most fit human being in the World isn't much of a match for a saber-toothed tiger (or any number of modern day predators) without the benefit of this [wikipedia.org]. It's pretty amazing when you think about it -- in spite of all the negatives (how many other animals routinely die giving birth?) associated with the human brain we still survived and clawed our way up the food chain.

        And without any concept of a nation-state to organize them

        Did we really have a con

    • by Kenja (541830) on Thursday April 24, 2008 @07:07PM (#23191422)
      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!
  • by Anonymous Coward on Thursday April 24, 2008 @06:36PM (#23190984)
    http://en.wikipedia.org/wiki/Toba_catastrophe_theory
  • one arkload (Score:5, Funny)

    by 0WaitState (231806) on Thursday April 24, 2008 @06:50PM (#23191180)
    Isn't 2000 people about the capacity of Golgafrinchan Ark Ship B?

    Just saying...
  • by monoqlith (610041) on Thursday April 24, 2008 @06:56PM (#23191240)
    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.
  • by NewsWatcher (450241) on Thursday April 24, 2008 @07:08PM (#23191444)
    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.
  • by puppetman (131489) on Thursday April 24, 2008 @07:35PM (#23191806) Homepage
    the explosion of the Toba volcano, in Indonesia, that was believed to take humans to the brink of extinction: [nasca.org.uk]

    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.
  • by CrazyJim1 (809850) on Thursday April 24, 2008 @07:38PM (#23191836) Journal
    I want to learn more than just a short article. Anyone know where I can read the scientific papers on this?
  • by Beryllium Sphere(tm) (193358) on Thursday April 24, 2008 @07:38PM (#23191840) Homepage Journal
    The most intelligent land animal almost went extinct, the second most intelligent land animal is an endangered species now, and a lot of the great apes are in trouble. Dolphins are doing OK, whales would be fine except for us, but neither is likely to develop technology.

    Are we going to find life on other planets but discover that high intelligence is rare?
  • by raaum (152451) on Thursday April 24, 2008 @08:08PM (#23192160) Homepage
    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 [ajhg.org]

    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.
  • by CustomDesigned (250089) on Thursday April 24, 2008 @09:03PM (#23192658) Homepage Journal
    They are just guessing about "harsh environmental factors". The DNA evidence just says they split up and came back together. In fact, there is a story in Genesis about a similar scenario. Population is reduced to 8 via global catastrophe. Increases to several thousand near Tigris and Euphrates. God then changes the language into 70 different variants, and these language groups then scatter over the earth, and gradually come together again. Even if you regard the story as Myth, Myth comes from racial memory.


    If you don't like Genesis, there is a Hungarian Myth that tells the story of the Huns (one of the language groups) beginning with the tower of Babel (the Genesis story above). The best telling, IMO, is The White Stag [amazon.com], by Kate Seredy.

  • by ignavus (213578) on Thursday April 24, 2008 @10:50PM (#23193498)
    Isn't this genetic bottleneck already credited to the Mt Toba explosion (Indonesia) which happened about 70,000 years ago?

    The Mt Toba explosion is believed to have been so huge (vastly larger than Krakatoa) that it plunged the whole earth into a "nuclear winter"-like period (just look up "Mount Toba" or "Toba catastrophe theory" in Wikipedia).

    In any event, we already knew that there was a genetic bottleneck about 70,000 years ago, as those Wikipedia articles indicate. What's the real genetics news here?
  • Mitochondrial DNA (Score:5, Insightful)

    by CrimsonAvenger (580665) on Thursday April 24, 2008 @10:50PM (#23193502)
    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.

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