Posted on 12/10/2006 2:44:11 PM PST by Alter Kaker
A surprisingly recent instance of human evolution has been detected among the peoples of East Africa. It is the ability to digest milk in adulthood, conferred by genetic changes that occurred as recently as 3,000 years ago, a team of geneticists has found.
The finding is a striking example of a cultural practice — the raising of dairy cattle — feeding back into the human genome. It also seems to be one of the first instances of convergent human evolution to be documented at the genetic level. Convergent evolution refers to two or more populations acquiring the same trait independently.
Throughout most of human history, the ability to digest lactose, the principal sugar of milk, has been switched off after weaning because there is no further need for the lactase enzyme that breaks the sugar apart. But when cattle were first domesticated 9,000 years ago and people later started to consume their milk as well as their meat, natural selection would have favored anyone with a mutation that kept the lactase gene switched on.
Such a mutation is known to have arisen among an early cattle-raising people, the Funnel Beaker culture, which flourished some 5,000 to 6,000 years ago in north-central Europe. People with a persistently active lactase gene have no problem digesting milk and are said to be lactose tolerant.
(Excerpt) Read more at nytimes.com ...
The East African thing had to be disease. If Vitamin D helps you ward off bacteria attacking your body, it's useful to be able to consume it (in milk) as an adult.
I've noticed that even our numerous pro-evolution guys still hold out for all sorts of quasi-supernatural explanations when a simple reference to an existing DNA methylation or "control gene" peer reviewed report would be sufficient.
This will take time ~ and, if that article (the one you C&Pd) is typical of what we face, it will take an awful lot of time ~
Experiments must be conducted numerous times to prove that these differences to not prevent interbreeding.
Find volunteers ~
Normal human beings do not have this change.
Time to read!
The Sa'mi, closely related to the Europeans, live in the far North where no grass grows. They have a variation in a gene affecting digestion which results in many of them reacting to wheat gluten as if it were poisonous.
Although modern Sa'ami number under 100,000 people a full 1% of white Americans have this same gene. That's 2,250,000 people! An even larger number of such folk live in Western Europe.
The gene is not harmful if you never eat wheat, barley or rye. It is disastrous if you have a large appetite for white bread.
Most of the references to this genetic situation are 6 years or less old, which gives you some idea of how long anyone has had a clue about the cause. You can cure it in three days by not eating the offending products.
I know a gentleman with a celiac problem all his life. Although he's in his 80s he gave up bread for 3 days and his problem is gone. Just to test it he ate an icecream cone. It came back instantly.
The Eskimos have similar genetic arrays.
Now, is this genetic difference a disaster, or simply a "difference"? Can you eat as much seal liver as an Eskimo? Or, do you have a genetic disorder that prevents you from consuming a substance with maybe a thousand times the safe level of mercury and other heavy metals? If you can't do that then, from the Eskimo perspective, you may well be considered horribly handicapped with a dangerous disease.
"Genetic meltdown" depends on where you live and what you eat.
I gather cattle were domesticated in Europe but once ~ and that was the aurox.
Interesting article, thanks for posting it.
Of course, the anti science luddites will misunderstand, and try to use the bible as a science text.
But, for everyone else, its a fascinating report and we are just learning about the complexities of human evolution.
I'm getting sentimental for the old street fights we used to have here.
From the info I've seen, milk naturally contains little Vit D...that's why it is fortified..though I suppose it would help supplement other things in the diet.
However little there is, you can use it.
Yep.
No, error catastrophe is definable and the human genome is very close if not in reproductive error catastrophe.
"If the offspring have on the average one harmful mutation each, then the population will degenerate; this is called "error catastrophe." This puts a bound on how many non-neutral mutations can occur per generation. It cannot be much more than about one per generation, and in fact, it must be significantly less, since most non-neutral mutations are harmful."
http://www.cs.unc.edu/~plaisted/ce/genetics.html
"In man, the mutation rate per generation is high, the variability generated in the population is comparatively low, and most mutations are fixed by drift rather than selection. The variants of a gene are in general more deleterious than in E. coli. There is a discrepancy in the published mutation rates: the rate of mutation fixations in human populations is twice or four times higher than the individual rate of mutation production, a feature which is not consistent with current population genetics models."
http://www.springerlink.com/content/jn3m132k451w1974/
"Observation suggests mutation rates are actually alarmingly high. Since mutations are harmful this means that error catastrophe is probably approaching for many species. One of the signs of genetic deterioration is infertility. Several studies have suggested that human infertility is increasing at 1.5% per annum. Infertility in some creatures (such as the Everglades alligator, and the Florida panther) is close to crisis point. If observed mutation rates are extrapolated back into the past one reaches the conclusion that life cannot have existed on earth for very long. If observed rates are projected into the future one must conclude that life does not have many centuries left. Observed mutation rates suggest that life is a short-term phenomenon."
http://www.refcm.org/RICDiscussions/Science-Scripture/X%20Evolution/introduction_to_evolutionary_bio.htm
A mutation is harmful or not harmful depending on how you look at it.
No I am not. I so stated. The gene for lactase is present and functional. A mutation does not "disable" that gene in the condition that we are discussing. What is "disabled" is the switching off of that gene. This gives the possessor of that mutation the ability to keep digesting the lactose later on in life. If you had read the article which I had posted you would also have realized that was mentioned in this.
Olds and Sibley (2003) characterized the functional role of the C/T(-13910) and G/A(-22018) (601806.0002) polymorphisms in regulating lactase gene transcription. Human intestinal cells were transfected with variant/promoter-reporter constructs and assayed for promoter activity. A 200-bp region surrounding the -13910C variant, associated with lactase nonpersistence, resulted in a 2.2-fold increase in lactase promoter activity. The -13910T variant, associated with lactase persistence, resulted in an even greater increase. The DNA sequence of the C/T(-13910) variants differentially interacted with intestinal cell nuclear proteins. The authors concluded that the DNA region of the C/T(-13910) lactase persistence/nonpersistence variant functions in vitro as a cis element capable of enhancing differential transcriptional activation of the lactase promoter.
Au contraire, it is not 'returned'. It never left in those individual genomes where the shut-down sequence is disabled.
You did not understand what I stated, because you are merely repeating what I stated. The quotes I put around the words I post are there for a reason.
What we are dealing with here is a complex system
Exactly my point. Look at my post 79. You are considering the situation as in figure one. I am explaining that the situation is like that in figure 3.
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