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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."
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.
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?
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