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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."
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.
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!
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.
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