Posted on 01/08/2004 9:00:45 PM PST by neverdem
A team of California geneticists has found that many of the world's peoples are genetically adapted to the cold because their ancestors lived in northern climates during the Ice Age. The genetic change affects basic body metabolism and may influence susceptibility to disease and to the risks of the calorie-laden modern diet.
The finding also breaks ground in showing that the human population has continued to adapt to forces of natural selection since the dispersal from its ancestral homeland in Africa some 50,000 years ago.
The genetic adaptation to cold is still carried by many Northern Europeans, East Asians and American Indians, most of whose ancestors once lived in Siberia. But it is absent from peoples native to Africa, a difference that the California team, led by Dr. Douglas C. Wallace of the University of California, Irvine, suggest could contribute to the greater burden of certain diseases in the African-American population.
Other experts praised the findings about adaptation to cold but said the role of mitochondria, relics of captured bacteria that serve as the batteries of living cells, in these diseases was less certain.
The genetic change affects the mitochondria, which break down glucose and convert it into the chemical energy that drives the muscles and other body processes. But the mitochondria will generate heat as well, and less chemical energy, if certain mutations occur in their DNA that make the process less efficient. Just such a change would have been very helpful to early humans trying to survive in cold climates.
Dr. Wallace and his colleagues have now decoded the full mitochondrial DNA from more than 1,000 people around the world and found signs of natural selection. By analyzing the changes in the DNA, they have been able to distinguish positive mutations, those selected because they are good or adaptive, from negative or harmful mutations. In today's issue of the journal Science, they report that several lineages of mitochondrial DNA show signs of positive selection.
These lineages are not found at all in Africans but occur in 14 percent of people in temperate zones and in 75 percent of those inhabiting Arctic zones. Dr. Wallace and his colleagues say this correlation is evidence that the lineages were positively selected because they help the body generate more heat.
Until now, most genetic change in the human population since it left Africa has been thought to be either random or just the elimination of harmful mutations. The evidence of the new analysis is that positive or adaptive selection "played an increasingly important role as people migrated out of Africa into temperate and Arctic Eurasia," the California team writes.
One implication is that everyone is adapted to a particular climate zone, and that moving to different zones may cause certain stresses. Mitochondria of the lineages found in Africa, Dr. Wallace suggests, may contribute the extra burden of certain diseases found among African-Americans, like diabetes and prostate cancer.
His reasoning is that African lineage mitochondria have never had to develop a mechanism for generating extra heat. So when an African-American and a European-American eat the same high calorie diet, the European's mitochondria burn some calories off as heat but the more efficient African mitochondria are liable to generate more fat deposition and oxidative damage, two results that could underlie the higher disease rates, Dr. Wallace said.
Separately, some of the European mitochondrial lineages appear to protect against Alzheimer's and Parkinson diseases and to be associated with greater longevity.
"Therefore," the California team writes, "to understand individual predisposition to modern diseases, we must also understand our genetic past, the goal of the new discipline of evolutionary medicine."
While many scientists study the genes of the human cell's nucleus, Dr. Wallace has focused on the tiny mitochondrial genome for 33 years. Along with the late Dr. Allan Wilson, he has pioneered the tracing of the 20 or so mitochondrial lineages found in the human population, all of which link back to a single individual known as the mitochondrial Eve.
Several other experts said that Dr. Wallace's ideas were promising but that the role of mitochondria in degenerative diseases had yet to be established. "It's a very attractive idea and may well turn out to be right, although the biochemical evidence of uncoupling differences between the mitochondrial lineages has yet to be nailed down," said Dr. Lawrence Grossman, a mitochondria expert at Wayne State University.
Dr. Mark Seielstad, a population geneticist at the Genome Institute of Singapore, said the positive selection was likely to have been a "major architect" in shaping mitochondria and that Dr. Wallace's work should throw open discussion of the subject.
Two experts on mitochondrial disease, Dr. Michael Brown of the Mercer University School of Medicine in Macon, Ga., and Dr. Gino Cortopassi of the University of California, Davis, said Dr. Wallace's ideas about African mitochondria made sense but had yet to reach practical significance. "We've not yet got to the stage of being able to give advice to African Americans," Dr. Brown said.
Dr. Wallace says that climatic selection may have operated on the human population from the moment it moved north of the African tropics. Most such pioneers died but two lineages, known as M and N, arose in northeast Africa some 65,000 years ago and might have been adapted to temperate climates. Almost everyone outside of sub-Saharan Africa has mitochondria descended from the M and N lineages.
It looks that way...and to the benefit of us all. Color is just one varible in the genetic mix, and probably a minor one as it relates to the genetics of medicine.
Wishful thinking, yes. More specialty = more expense. Just think, in 1900, there wasn't a specialty titled archaeologist or anthroplogist. What will there be in 2050?
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I'm glad you had a few chuckles CM55. Maybe I'm mad, but I think most of us here are politically conservative, and most conservatives have "Ice Age Ancestors" that are white males as well as the converse, and that as far as most African-Americans are concerned we're racists.
This article rebuts the notion, prevalent in the African-American community and re-inforced by the major mainstream media, that African-Americans receive inferior medical care causing them to have increased morbidity and mortality because of a racist society that provides insufficient funding of their health care needs, and a predominantly white and racist medical profession that gives them only second rate care.
Maybe it's been too long since you looked at the major media like the NY Times, CNN, ABC, CBS, and CBS. AFAIK, the last three of them had a weekly segment dealing with the big medical story of the week from the Journal of the American Medical Association or the New England Journal of Medicine, which have an issue almost every week. There have been quite a few stories from those journals that inferred African-Americans received inadequate medical care because of some latent racism on the broadcast evening news.
Don't feel bad, I rarely watch ABC, CBS or NBC either. From 6:00 PM EST, I've been watching Brit Hume on FNC for years now. But you should know what your political enemies are thinking, and that's why I still scan the NY Times. Every once in a while, you'll find stories like this, that slip through the cracks.
As far as racism goes, it's the argument of nature versus nurture, with conservatives mostly saying nature is the predominant force which determines sociological outcomes, and liberals saying it's the lack of nurture, i.e. racism, which predominates.
Since the Great Society and all the programs that followed, I can't think of anything else the "Whites" of this country could do in order to show that they are not racist, but show them the facts.
IMHO, here you have the "paper of record" giving you a new, breaking news "gift horse" that you want to shuffle off out of sight, when it deserves the widest dissemination.
Bear with me, the hour is late. I believe you're saying Darwin is/was correct. I hope so because natural selection from random, natural mutations explains the antibiotic resistance of formerly sensitive pathogenic organisms after exposure to a previously lethal antibiotic, i.e. to the organism, if the patient finished the prescription, e.g. a patient didn't finish the complete course of treatment prescribed by the physician because the patient started to feel much better and didn't finish her/his medicine.
The magazine Science is not intended for general circulation, but the NY Times is. It's too bad you can't appreciate the import. I shall try a few more times before I surrender regarding science as an appropriate topic on FreeRepublic.com. I regret you are unable to appreciate what is new information. LOL
How is it that OJ Simpson and Madonna were breaking news and a new scientific conclusion isn't. OK, so the jocks like to make fun of the geeks, but that's only until the geeks fire them and tell them to work for someone else.
Shocking. How can this be? The creationists keep insisting that all mutations are harmful.
Thought by whom? Maybe some PC ideologues, but certainly not anyone with a functioning brain.
Well, this makes sense empirically. All of my ancestors came from arctic regions (if you go back far enough), none that I can recall were extremely fat, most only required one blanket for sleeping even during the coldest winters, all of them lived well into their late 80s and 90s but had brittle bones. Guess I'd better start taking more calcium and magnesium.
Swedish patriarch's first comment upon arriving in America: "Ya, sure...vell, ve go north!" ROFL! I always wondered why great-grandfather Alfred didn't bring the family to Florida.
I suppose it depends on one's point of view. Scandinavians are noted for taking very hot saunas and then immediately rolling in the snow, eating Lutefisk and Sylta (you don't want to know), and as my dearly deceased relatives would tell it - walking 10 miles barefoot in the snow each way to school (actually, I've tried walking barefoot in the snow...exhilarating!). I think it's up for debate as to whether these are the result of beneficial mitochondrial mutations or not. Then of course, my family could just be plain nuts! LOL
That's news to me. I believe that God created everything but I'm agnostic on how He did it. There's no doubt that evolution is a fact but, as someone with degrees in both chemistry and chemical engineering, I'm just not quite sold on the popular notion that pretty much anything can happen via evolution given enough time. The chemistry is very complicated.
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