Skip to comments.Ice Age Ancestry May Keep Body Warmer and Healthier
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.
But we might be near the point where differences in medical outcomes could be explained by something other than racism in society in general and the medical establishment in particular. BTW, more prostate cancer and less osteoporosis is also correlated with higher testosterone levels in Africans as opposed to Caucasians.
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I'm Danish/Scottish/Magyar... I just love the cold. My house is right now at 60 deg f and I'm wearing shorts and a sleeveless shirt...
Very good article neverdem. I believe within the next ten years there will become a branch of medicine perhaps titled 'genetic medicine.' There are clearly differences in the races (and every thing in between) and the effectiveness of different medicines within that race...and I'm using the word 'race' as meaning a specific genetic signature. If you like this sort of 'stuff', read the below linked article: (It blows my mind)
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