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December 12, 2007

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PeterUK

Then how do you account for Semanticleo.some kind of regressive gene?

boris

we are talking about gene expression, not gene mutation

2 quick points.

The study also claims that modern gene flux probably makes further differentation impossible and likely reversed from now on.

Evolution is less about mutation than selection anyway. "Harmless" mutations tend to accumulate in "junk" DNA until some other factor, such as selection or environment confers an advantage which drives wider dispersion of it into the general population.

Rez

"Africans have new genes.." My layman understanding on the science is that there is no evidence of genes being added to life; but lots of evidence that certain indiginous groups have lost genetic material over the years due to their isolation from other people.

vnjagvet

This is the case, he said, because since humans dispersed from Africa to other parts of the world about 40,000 years ago, there has not been much flow of genes between the regions.

So in a sense, in the USA we are all African Americans!!

Charlie (Colorado)

Tom, I'm willing to bet the authors know the difference between gene expression and mutation.

As to the ear wax thing, nothing says a mutation has to be beneficial. if you have an isolated population and a relatively dominant mutation, then it will eventually show up in a lot of the population.

boris

nothing says a mutation has to be beneficial

More likely that the trait providing an advantage is gene linked to a harmless wax side effect. A strongly selected for trait can even carry along a harmful side effect, ie sickle cell.

Peterargus

Actually the authors believe the mutation for lactose tolerance occurred AFTER cows were domesticated. Apparently, once it appeared, it was under very strong positive selection and spread rapidly in Europe.

There was an increase in # of mutations as the population size increased, a number of which were selected for as the types of environments which humans lived in increased in number as well.

About the earwax. According to this NYT article: http://www.nytimes.com/2006/01/30/science/30ear.html
the gene controlling earwax moisture also has a role in sweating so the real question to ask is what is the benefit for Asians of sweating less?

Jim Miller

" . . . what is the benefit for Asians of sweating less?"

Well, the Asians they are talking about are thought to have evolved in a very cold climate. And, as a cross country skier, I can tell you that sweating less is a big advantage in cold weather.

Other traits common to, for instance, most Chinese, are also thought by some to be adaptions to cold weather.

According to the Cavalli-Sforza book on diasporas (which may be out of date), northeast Asians (Chinese, Mongols, Japanese, et cetera) are quite different geneticallly from southeast Asians (e. g. most Indonesians)

Crimso

Outstanding comments. As someone who has credentials in biochemistry, I can tell the lurkers that a good amount of the discussion to this point sounds as though it's coming from people who know what they're talking about. My initial impulse was to comment that the question of expression vs. mutation is a good one. The upthread cite of sickle cell is pertinent in that it is unquestionably a case of mutation, and there are many such examples, if only in the case of mutagenizing cells to select drug-resistant cell lines. I'm not sure how much is known about evolution as a function of altered gene expression vs. gene mutation. But ultimately the heritable changes in gene expression are in fact due to "mutation" in the sense that changes in base pair sequence of DNA either results in changes in promoters, enhancers, etc. or in the proteins that bind them. I think it's less about mutation vs. expression, and more about the selective advantage gained (a la Boris above). Mutation and expression would be the means by which the changes occur, but such changes are only detectable long-term if they confer an advantage.

Neo

The even more recent phenomenon of "modern medicine" now was genetic lines that would have died off due to natural causes continuing to foster genetic reproduction of "flawed" lines.

Soylent Red

So in a sense, in the USA we are all African Americans!!

So where the hell are my 40 acres and a mule?

glasater

"So where the hell are my 40 acres and a mule?"

One could look at the current sub prime mortgage situation and the proposed remedy as just that very thing.

Back to on topic--Nova did an interesting program on DNA and a study of identical twins where one was very healthy and the othe quite ill.
It was pointed out that plants are more genetically complex then humans.

Walter

But ... but ... but ... Huckabee tells me that evolution is a crock. How can this be?


His beliefs are likely to affect his policy formulation. How much money will he devote in his budgets to genetic research?

And he claims to be concerned about education. Bah!

vnjagvet

Who says I wasn't on topic, glasater? After all, I quoted from Tom's postL:>)

Just trying to inject a bit of humor into the thread. That is all I have the capacity to contribute at this hour.

glasater

Vnjagvet--It wasn't your comment but my response that was off topic. And was trying to reign myself in.
Your comments are always terrific!!

Neo

This is golden.

Remember those glaciers in Greenland that were melting.
Gore et al told us is was part of the CO2 problem.
Now, it appears that "settled science" gives way to the magna problem.

Whitehall

One of the prime methods for mixing and diffusing human genetic material is warfare. Remember the stories of the rape of German women by Russians following victory in WWII?

While this continues on small scales (Congo, Darfur), big technological wars are so much more violent to civilians that its effects are blunted.

I'd say we should be thankful that our local gene pools are diverging!

Clyde

Dry ear wax allows one to hear the sound of one hand clapping.

It's a zen thing; you wouldn't understand!

kim

Magmificent, that Jay Radar.
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