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."

Comments

More Info & complete paper

[MonkeyBoyo]

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.

Lactose intolerace

[Nice2Cats]

The ability to digest milk after puberty is still only widespread in Caucasians and some parts of Africa, as I happen to know because I am one of the Caucasians who is not a mutant and had to give up my ice cream orgies with puberty (puberty did have its compensations). This is why lactase pills (which contain the emzyme required to break down the milk sugar lactose into glucose and (I believe) galactose) are selling like mad.

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...

BBC's writer clearly didn't do his homework

[zaad]

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

[MonkeyBoyo]

What triggered the writeup was the The American Society of Human Genetics journal article. For some reason the SFGate link also discussed the genetics of lactose intolerance, and here I will give some references and discuss how this is relevant to early human evolution and perhaps bottlenecks.

Genetic lactose intolerance (= hypolactasia = non-production of lactase enzymes past weaning) has a hereditary component (Sahi 1994)

It is assumed that thousands of years ago all people had hypolactasia in the same way as most mammals do today. At that time in cultures where milk consumption was started after childhood, lactase persistence had a selective advantage. Those people with lactase persistence were healthier and had more children than people with hypolactasia, and the frequency of the lactase persistence gene started to increase.

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:

it seems most likely that the European and Arabia-Sahara centers of LAC*P prevalence, and the Uganda-Rwanda center (if it in fact exists), arose independently. Population movement and gene flow can be very extensive and, no doubt, have played a substantial role around the centers. Despite the efforts of some authors to find a common origin in the ancient Middle East, it is simpler to suggest independent origins than to postulate gene flow from the Middle East to Scandinavia and to the interior of East Africa. The problem might be resolved in the future if gene sequencing could show that the LAC*P alleles in Sweden and Saudi Arabia are, in fact, the same or are distinct forms of the gene with a similar function.

â¦

Finally, the LAC*P and LAC*R genes are interesting far beyond their biomedical significance. Along with linguistics, archaeology, and physical anthropology, further research on lactase genes and other genetic markers will provide clues to the prehistory of peoples, their migrations and interminglings, and the origins and development of major language families.

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?