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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.
Anyway, farts is the problem, but indirectly. If you are lactose intolerant, you're body can't break down lactose, so you get few calories from it. The energy is wasted on fart generating bacteria.
Hey, I never knew you could watch a post drop each time you hit preview!
'SBEMAIL!' is better than a goat!!
According to a new study, the old study was right!
-BM
http://melbournephilosophy.com/
First off, tits and beer rock. Sports... I can take of leave.
As for the parent comment, I studied anthropology in school and did a rather large term paper on genetic diversity. Not the topics in the articles exactly, but enough that I do know what I mean, and I think I know what they mean.
As for the genetic diversity, usually, they mean exactly what the term would imply. The different genotypes that occur in a given sample. In humans, it doesn't mean the difference between the two most genetically different people. The problem with discussing the difference between the two most genetically different people is that it implies a range. That's not the case, there isn't some genetic continuum or between disparate people. There are other people who might not be as genetically different as the two extremes but possess novel genes that the two extremes lack, thus they contribute to the over all diversity.
Your problem (other than being a contrariam who would rather criticize the discussion than contribute to it) is that you're used to thinking in terms of the quantifiable and the continua. There is a continual, quantifiable spectra of light for example, so you try to apply this thinking to other non-continuous phenomena.
If geneticists needed to discuss gene diversity in some sort of quantifiable measure, it would eliminate their ability to discuss relevant topics. Unless you are referring to a specific sample of genes, you can't quantify the diversity. So you just call it diversity instead of lamenting the lack of a standardized "Gene-ino" quanta. Just because they haven't sampled every gene of every human doesn't mean they can't make statements about human genetic diversity.
And another thing, it doesn't really matter which group of chimps they were talking about. The point stands even if it is only true for a single chimp troop out of all the chimp troops in the world. If somewhere out there there are 60 - 70 chimps with more diversity than all of humanity, then chimps possess more diversity, and a scientist will ask why.
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...
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?
Actually it was Alister Hardy who first coined the hypothesis. Desmond Morris mentions it in passing in 'The Naked Ape' and it was picked up by Elaine Morgan as an alternative to what she called 'The Mighty Hunter' narrative of human origins in her 1972 pop feminism book 'The Descent Of Woman'. It is Morgan who is the published writer most identified with Aquatic Ape Hypothesis.
Pro/anti flamefests are a regular occurence on various human origins fora which is probably why the earlier post got moderated as flamebait.
Regards
Luke
#include witty_one_liner.h
Lactose intolerance is the norm in many parts of the world.
Tom Swiss | the infamous tms | my blog
You cannot wash away blood with blood
"On a related note, mitochondrial DNA seems to indicate that our common mother (mitochondrial eve) existed ~6000 years ago, less than the 70,000 years proposed here."
One nit to pick. Going back to the original "Research News" article in Science (vol 279 issue 5347 pg 28-29), we see that instead of this being evidence for a ~6000 year old mitochondrial eve, we have to reconsider some of our beliefs about mitochondrial DNA (mtDNA), or more specifically a region of mtDNA called the D-loop, which comprises only 7% of mtDNA and which most mtDNA studies have used. One of the biggies is that most mtDNA studies use "so-called "noncoding" sequences of the control region of mtDNA, which do not code for gene products and therefore are thought to be free from natural selection." to quote the article. Another is to check and see if we are instead hitting "hotspots," regions with above-average mutation rates; hotspots will have more back- and parallel-mutations which will cloud the picture. A third is that the mutation rate may vary over time. A fourth is to investigate the issue of heteroplasmy--having multiple mtDNA sequences, even though for a given region there should be only one. For a while it was thought to be rare, now 10-20% of the population could be heteroplasmic. All of these issues would need to be addressed by the creationists before it could be considered evidence of a ~6,000 year old mitochondrial eve rather than a problem with the underlying assumptions of the technique. Indeed, with the advancement of our ability to manipulate and sequence DNA, we no longer have to utilize only 7% of the mtDNA--we can sequence the whole thing--all 16,000 or so base pairs of it. A recent study published in Nature (vol 408 pg 708-713, Dec. 2000) using mtDNA--all of it--found that the D-loop (used in most mtDNA studies) does not have a constant mutation rate. The study goes on to show (again using the whole mtDNA sequence) that the date of "mitochondrial eve" is about 170,000 years ago. A more reader-friendly report by the author of the Nature paper can be found here.
> On a related note, mitochondrial DNA seems to indicate that our common mother (mitochondrial eve) existed ~6000 years ago, less than the 70,000 years proposed here. It was originally thought that mitochondrial eve existed ~200-250,000 years ago. However, new research in 1997 (off memory) indicated that mutations in mtDNA occurred far more rapidly than assumed (assumptions were based on evolutionary expectations for mitochondrial eve). This resulted in the new date. Take note: I've had many evolutionists come back and quote the original article saying "See! It says 200,000 years, not the 6,000 creationists quote. Just another example of creationist lies". However, they failed to look at the top of the article which was dated (Again, off memory) 1996, a year before the new research was discovered. I thought I'd mention that to save potential embarrasment.
Actually, the Loewe and Sherer letter cited by your favorite creationist Web site does not argue for a 6,000 year old mitochondiral eve; they merely mention in passing that that would be the untenable effect of basing a molecular clock on one specific mDNA site that has come under investigation. They spend the rest of their letter proposing ways of understanding the mutation rates that would naively yield the date that they themselves reject.
If you search for "mitochondrial eve" at PubMed and read the abstracts of more recent papers you will see other papers cautioning the use of mDNA for calibrating biological clocks.
Also, very recent articles are still dating the y-Adam to 50,000-170,000 years ago. This is somewhat problematic for people who misunderstand "mitochondrial eve" to be the female founder of the species and think she lived a mere 6,000 years ago, as she would have had to get bonked by a 44,000-164,000 year old man. [cite: Howard JM, '"Mitochondrial Eve", "Y Chromosome Adam", testosterone, and human evolution', Riv Biol. 2002 May-Aug;95(2):319-25 - though I have only seen the abstract, which is available on PubMed.]
Sheesh, evil *and* a jerk. -- Jade
Actually, the Loewe and Sherer letter cited by your favorite creationist Web site does not argue for a 6,000 year old mitochondiral eve; they merely mention in passing that that would be the untenable effect of basing a molecular clock on one specific mDNA site that has come under investigation. They spend the rest of their letter proposing ways of understanding the mutation rates that would naively yield the date that they themselves reject.
A little more background on the Parsons paper. Untill the Parsons paper, mutation rates in ALL mtDNA regions were believed to be neutral. The projection made by the creationist site use precisely the same mtDNA clock methods that where used by evloutionary scientists to predict the 100k year MTeve before the high rates were discovered. To that point the mutation rates for the 100k year old MTeve were generated off mutation rates predicted from the divergence between chimp and human mtDNA. Nobody had tried measuring actual mutation rates from human forensic evidence. Parsons was the first to measure observed rates, and discovered a mutation rate 20x higher than the rates predicted by the chimp/human calibration. Parsons rejection of this rate was primarily based on the ridiculously high rate compared to the relatively low differences between chimp and human mtDNA. If mtDNA was neutral and chimp/human diverged ~5ma then the observed mutation rate was impossible. Thus the non-neutrality of mtDNA was proposed.
If you search for "mitochondrial eve" at PubMed and read the abstracts of more recent papers you will see other papers cautioning the use of mDNA for calibrating biological clocks.
And most of them have been trying to justify the difference between observed mutation rates in mtDNA with those predicted from chimp/human divergence rates. The explanation has always been that the random observed mutation rate in current studies is different than the fixation rate over millions of years. Selective pressure and hotspots were random mutations cancel each other out are among proposed explanations. The creationist conjecture that the chimp/human divergence assumptions are wrong are rejected out of hand as ridiculous. The coincidental 6k years for MTeve and same approx date from biblical records is merely that, a coincidence. Some people though don't reject that big a coincidence as lightly.
From the Ontario Goat Milk Producers' Association
It seems physically(not trying to get in a social debate) that dark skin would only be advantageous(you don't burn as bad), less skin cancer?
Ideas either way.
I believe those with darker skin need more sunlight to produce enough Folic Acid and Vitamin D. Thus the adaptation to lighter skin when we moved North to the Cloudy Continent.
-Ansel.
G=C800:5