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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."
So do your part to ensure diversity, and make sweet love with someone genetically different (read: hot) under some power lines near a microwave running with the door open. "For the sake of the species" never made a better pick-up line.
(Just don't give her your name--she might expect you to help raise your special freak).
Thinking about that, I didn't make myself clear on something. What I was trying to say was that if a single troop of 60 to 70 chimps can have X diversity, shouldn't a group of 60 to 70 humans - a close relative of the chimp - also have X diversity. What struck me about the article is that their implication is that those 2000 people they say sired us had less diversity than 60 to 70 chimps.
Makes you wonder if it has something to do with human females being fertile year round. If I recall, chimp females are not. Because chimps can only mate at certain times, there is less oppurtunity for one male to sire all the children in a troop. In a human harem type social group, this could be easily accomplished which would cut down the genetic diversity considerably. Do this for a couple of generations and you might end up with a population with a depressed gene pool. Anyway, just arm chair theorizing off the top of my head. (Gotta use that anth degree for something.)
Arguably, in spite of our numbers, we're close to extinction now.
Hey, good to know we got out of it last time.
Sunlit World Scheme. Weird and different.
Here is the abstract from the The American Society of Human Genetics article, and here is Stanford's press release on the story.
And are the web pages of Marcus W. Feldman and Noah Rosenberg From Rosenberg's research page, here is access to a PDF of the journal article.
But being lactose intolerant was an advantage once fart-lighting was invented.
Do you even lift?
These aren't the 'roids you're looking for.
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."
being able to digest lactose became a survival advantage after dairy farming was invented.
So at some point some humans said:
"Hey lets invent dairy farming!"
"Hmm, but we're all lactose intolerant..."
"What the heck, if we take this crap every day we'll eventually mutate and some generations down they will be thanking us."
Nice long-term thinking there, thanks!
Within the next 50 years, about half of us will be dead!
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.
"I dare you to drink that."
"No, I dare you."
"Ok, we all dared, so we all drink."
Then they all got sick except one who not only brained them with a club and sired children with thier wives... After that, he taught his sons how he got all the foxy wives and they went to neighboring villiages...
The BBC had one of their unevitably brilliant documentations about the rise of mankind a few weeks again on German television where they pointed out that humanity must have been really, really close to the gutter before it exploded. Then this big, black rectangle came and showed them how to use the thigh bone of a pig to kill...oh, never mind...
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.
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 (such as the Chinese, apparently the character for ship is that story).
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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?
It's shocking how much better the San Francisco Chronicle article is to the BBC article.
Clearly both writers had the same source to work with, but the sfgate article was much more researched, thought-out, and nicely tied together. Even when I had only read the BBC article, I was shocked at how poorly structured the article was.
If you're only going to read one of the two, read the sfgate piece.
Genetic lactose intolerance (= hypolactasia = non-production of lactase enzymes past weaning) has a hereditary component (Sahi 1994) The Cambridge World History of Food (2000) has a good article on the science and geography of lactose intolerance. This problem is not caused by the gene that creates lactase but instead by another gene (LAC*R (lactase restriction)) that kicks in later and ramps down the primary gene. (The other allele LAC*P allows lactase production to persist) However that article says:â¦However in 2002 the LAC*P gene was identified and sequenced within a Finnish population and was found to be the same as those in the rest of the world. This means that genetic adaptation for adult milk drinking evolved early and all milk-drinkers have ancestors in some early population in the middle-east or Africa.
The problem with equating lactose intolerance with genetics is that people will see this as an either/or situation â" either you can eat it or you can't. The fact is that most intolerant people can consume small to medium amounts of lactose with no problem. Major milk problems are more often the result of allergies.
Eventually there is the issue of culture. Fermented milk products (e.g. yoghurt and cheese) may be easier to digest than raw milk. Do the cheese/yoghurt eaters have a cultural advantage? Or have they disadvantaged other cultures?
I don't expect the BBC to do an exhaustive search of all the peer review journals every time they do a science story, but they should at least check their own archives to help explain an curious conundrum like this one.
The date given for the bottleneck, ~70,000 years ago, coincides perfectly with the largest volcanic explosion in the last half million years. One that spewed thousands of times as much ash as produced in the 1980 Mt. St. Helens eruption.
The explosion of Toba in Indonedia around 74,000 years ago probably caused a greater than 5 degree drop in average global temperature that lasted over 6 years. 5 degrees may not seem like much but that global average may translate to over a 15C drop in the summertime temperatures in the temperate regions and would have devestating effects on many of the plants we relied on for food.
Point is that most of what I just mentioned (and much more) can be found in a few articles on their own web site:
"There is a thin line between ignorance and arrogance, and only I have managed to erase that line." - Dr. Science
I'm surprised that article didn't pick up on the theory that the bottleneck in the genetic line about 70K years ago might well have been due to the eruption of the Toba supervolcano that was regarded as one of the most significant eruptions in the last 2 million years. That kind of climatic change from such an eruption could well be responsible.
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