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Have Humans Come Close To Extinction?
waytoomuchcoffee writes "According to a new study, our virtually identical DNA indicates humans were close to extinction about 70,000 years ago. Another take on the same study tells how being lactose intolerant in adulthood was normal, and being able to digest lactose became a survival advantage after dairy farming was invented."
You're right of course, the article is too vague. It was really just musing onto the keyboard. I'm not advancing a theory or anything. There could be many explanations for the low genetic diversity including subsequent death of lineages, genetic advantages of a sub-group (the whole scikle cell anemia - malaria connection) etc. Also, there was some genetic bottlenecking, where an even smaller group populates most of the world and the remainder stays behind in Africa.
I remember reading that if you took any world wide sample non-Africans - ANY sample no matter how diverse - and an equal number of randomly sampled Africans from the same villiage, you'd find more genetic diversity in the African villiage. The argument being that there was some genetic bottneck on the way out of Africa and only a tiny minority of the gene pool actually left.
Oh, and if us Neaderthals were still cheesed about that whole cannibalism thing, we'd let you know. We're over it. We ate you guys too. It's all good.
The thing that should have bothered you is the utter ambiguity of such a claim. This is just one of those "newspaper statistics" that sound as though they mean something but don't.
What is the diversity of all humans? Is it more than the diversity between the two most different humans? What is the means of quantifying difference? Is there some standard, or are there lots of standards, or are there just countless ways, each of which yields a different answer?
What about the diversity in a group of chimps? Is that a family of chimps, or a small group randomly chosen from all chimps, such as one might find at some zoos?
I'm just not sure how to interpret the comparison of diversity between a small group (of chimps) and a large group (all humans). Size of group wouldn't have been mentioned, presumably, if it weren't part of the equation. What part?
Unless you know what it is they really mean, I'm not sure it makes much sense to go looking for deeper meaning.
"Those who have never entered upon scientific pursuits know not a tithe of the poetry by which they are surrounded."
I'm not sure I buy the article's argument that "humans" came close to extinction. I think another possibility is that what they're looking at is a speciation event: that's the point that homo sapiens sapiens branched off from immediate predecessors. If that group had been killed, we wouldn't be here, but I'm not sure the homo genus would have died off.
> So, either humanity dwindled down by chance to
.. its a well known phenomena, called the 'founder effect' - and the reason why those chimps in that troop are as genetically diverse as they are is because of gene shuffle between groups.
> 2000 people who happened to have little genetic
> diversity, or there was some common genetic
> trait that selected for those specific people.
> Or something. But then who knows... maybe
> chimps are just naturally genetically diverse
> and we're not... or maybe I just missed
> something that the writer thought was too
> technical for the article.
Nah, there's no extra explanation needed
Think about it; if you are isolated, alone and there is no one else around, the diversity is naturally going to suffer - interbreeding will see to that. However, chimps haven't gone through the same genetic pruning because groups/tribes mate with each other.
Something about that struck me. If the natural state of affairs is for a wide genetic diversity even in a small group - such as the chimps, then why wasn't there a similar diversity in the 2000 people who went on to sire the rest of us.
IANAG(eneticist), but I would say that this is most likely due to a concept known as founder's effect in population genetics. There looks like there's an interesting page curtesy of googlecache.
Think of it in these terms. Whatever your genetic diversity happens to be, if you reduce a population from two million down for two thousand, you're going to lose a lot of diversity. Further, especially that population reduction was due to some selection pressure (may immunity to some disease), you're going to target a very select subset of the population (known as hard selection). So what happens is that you end up with much less genetic diversity than you would have otherwise (diversity takes time to build up).
In the case of the chimps, if they've not gone through a recent "extinction" scare, and have had a long, long time for their genome to diverge and mutate, even if you just sample a small group of 60 or so chimps, they're going to exhibit much more diversity simply because they've had so much more time for their genome to wander or drift.
Does that make more sense?
(Without reading the article...)
:)
I don't know much about genetics but....
IIRC genetic diversity also indicates how
old a 'species' is.
Hence, given the widespread genetic diversity in chimpansees and the low genetic diversity in humans, you can deduce that chimpansees have been around much longer than humans.
The other explanation could be that a single group of humans were so succesfull at some point in the past that we are all descendants of that group.
(oops, thats the same as coming close to extinction - just phrased a different way
There are groups of people in the world that are very much genetically distinct from the rest of us. (Eh, Read "The Naked Ape" by whatshisname...)
( Isolated pockets of genetic diversity...stuff like that )
Another explanation could be the life span of chimpansees...anyone know how long they life in the wild? Short lifespan? Females are almost constantly pregnant. Now compare that to humans...long lifespan...relatively low pregnancy rate ( welll...) That could also explain the difference in genetic diversity?
Phrased another way - for an equivalent period of time there might have simply been more generations of chimpansees compared to generations of humans.
Could that account for the difference in genetic diversity (as well)?
Since evolution is a two step process: first mutation, then selection, we wouldn't expect selection to increase diversity. mutation is responsible for increasing diversity. selection decreases diversity. diversity might be a selective advantageous property of populations, and in some cases there might evolve (by selection) functions that increase diversity. sexual reproduction is one such thing.
Logic, macros, and more
Well, there are other factors as well. Normally, that troop will outbreed quite a lot with other troops, which will keep it diverse and smother out much of the randomness.
But if there are only on the order of hundreds of individuals available, small random effects will start to have an impact. Not every individual will reproduce equally effectively, even if they are genetically equally viable - due to accidents, and other random effects, you will tend to get an inverse power-law like distribution with small numbers oif individuals. So, in that troupe of 2k individuals, maybe twenty to fifty of them will in reality be the progenitors of the majority of the offspring - others will have caught a disease, or be infertile, or have their children all die early, or have a falling out with their partner or whatever.
By the time the population is large enough that individual chance is smothered out, the individuals will in practice all stem from a small subpopulation of those that were available at that earlier time.
Trust the Computer. The Computer is your friend.
> Could the biblical story of Noah's ark explain this, as a worldwide flood leaving only a single family of eight alive will achieve this effect of everyone having similar genes.
No. As others have already pointed out, (a) the biblical flood supposedly happened 4000-5000 years ago, not 70,000 years ago, and (b) geology soundly refutes any and all claims of a global flood (this being realized by the parsons who invented geology, already by 1820), and (c) all animals would also have to have genetic bottlenecks at the same time (or more recent, due to other causes), and (d) there are a very large number of additional problems with the flood yarn, which we can go into if you wish.
Of course, you could always sweep everything under the rug by claiming that God patched everything up with miracles afterward, to make it look like the flood never happened. But theology is no more capable of investigating such bizarre claims than science is.
> Before you mod me down into oblivion for sounding like a self-righteous Creationist, do note that other cultures have references to a catastrophical flood
And lots of cultures have references to multiple gods. Do you put the same weight on those traditions, or do you just pick the ones that you think supports your own position?
> (such as the Chinese, apparently the character for ship is that story).
I think that particular claim is that the character is the composition of the characters for "8" and "mouth". Extraordinarily weak evidence for a flood, even if the claim about the symbols is true. Basically someone has noticed that out of all the writing systems in the world they can find one symbol that has a very weak association with one story in their favorite mythology. This is nothing more than a posteriori data scumming.[*] Given the amount of data they have to work with, the only surprise is that they haven't found a better match with the target mythology.
[*] I use the roguelike term "scumming", since the obvious "data mining" has a very different connotation.
Sheesh, evil *and* a jerk. -- Jade
As I remember from high school biology, doesn't only a small percentage of our DNA code for useful information? The reset was just junk that is cut out during protein synthesis (introns? extrons? I forget the terms...) Is this included in the study? Could it be that chimps are also extremely genetically uniform in the areas that matter, but they have more diverse "junk" material than us? Then again, I seem to remember someone saying that the "junk" DNA plays a vital part in evolution? Argh, guess I shouldn't have slept through those classes! Now we'll all become extinct!
how being lactose intolerant in adulthood was normal, and being able to digest lactose became a survival advantage after dairy farming was invented.
Preceding the domestication of cattle; for lactose intolerant to arrise, it must have offered some survival advantage.
In 1959 Koshima macaque monkeys learned to swim, ever since then the entire group can swim...
Also in American colonial times the only human swimmers were witches...
The other arguments are interesting, but the swimming one is weak.
"I'll have a Guinness, no wait, make that a Coors Light" -Grad student I work with, who shall remain anonymous...
You need diversity to preserve the diversity. If you have a small population and they start inter-breeding, you'll wipe out most of your diversity in fairly short order because, before long, everyone will have the same common set of ancestors (and thus, a relative lack of genetic diversity). In short, past history is everything in genetics.
Vanity of vanities, all is vanity...