Posted on 04/23/2005 8:30:41 PM PDT by Lessismore
MILWAUKEE, WISCONSIN--About 1200 researchers gathered near the shores of Lake Michigan here from 5 to 9 April to discuss early Englishmen, the birth of modern humans, and Stone Age weapons.
In the past 15 years, a flood of genetic data has helped propel the Out of Africa theory into the leading explanation of modern human origins. DNA from mitochondria (mtDNA), the Y chromosome, and ancient humans each suggest that the ancestors of all living people arose in Africa some time after 200,000 years ago, swept out of their homeland, and replaced archaic humans around the globe without mixing with them. But at a genetics symposium, two independent groups presented data from the X chromosome hinting that modern humans interbred with other human species: The teams found possible traces of archaic hominids in our genes. "Just as the Y and mtDNA data seemed to have settled it, the new data revive the question [of interbreeding]," says Stanford University's Joanna Mountain, co-organizer of the symposium. "The controversy is not settled." Geneticists Makoto Shimada and Jody Hey of Rutgers University in Piscataway, New Jersey, presented an intriguing haplotype--a set of genetic mutations inherited together--that appears to have ancient roots in Asia rather than Africa. Shimada sequenced a 10.1-kilobase noncoding region in 659 individuals from around the world. Overall, the genetic variations were most frequent in Africa, just as expected if our ancestors were a subset of ancient Africans who migrated out of that continent. But one rare variant, appropriately named haplotype X, appeared in nine individuals from Europe to Oceania but was entirely absent in Africa. Shimada estimated that the haplotype arose 1 million years ago, long before the modern human exodus from Africa. "Haplotype X is difficult to explain by the recent African origins model," says Shimada. "It's very old, it's rare, and it is widespread outside of Africa."
In independent work, geneticist Michael Hammer of the University of Arizona in Tucson offered a similar example. Hammer and postdoc Dan Garrigan identified a 2-million-year-old haplotype in the RRM2P4 region of the X chromosome that is common in East Asia but vanishingly rare in Africa. Their work, published 2 months ago in Molecular Biology and Evolution, raises the possibility that the haplotype arose in very ancient Asian populations, presumably of Homo erectus, an ancient human once found across Asia. "This is what you'd expect if you had introgression" between modern humans and H. erectus, Hammer said.
But at this point several other explanations are possible. Hey of Rutgers acknowledges, for example, that haplotype X may be present in Africa but was missed by spotty sampling in that continent. "Simply observing those [examples] is not sufficient to rule out one model or another," cautions Mountain. "What you need is 10 or 50 loci--one or two is not sufficient." Hammer, for one, thinks that these preliminary data do "speak to some archaic admixture. The few [loci] we've done so far are so suggestive that it gives me great excitement to continue sequencing more loci."
Prefessor Stephen Oppenheimer has documented the 'X' gene in American Indians and some Europeans and no-one in between. His explanation is that the Toba eruption 74,000 years ago killed everyone in between and broke the link. Oppenheimer opines that humans were probably in Australia prior to the Toba eruption.
why not?
the ancient greeks thought we were descended from the blood of snakes dropped on the ground.
Ping.
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I have an idea that I've been working on for a while, here it is:
Evolution is occuring every minute, every hour and every day of every year all over the world. Let's take humans.
Women have something called 'spontaneaous abortion' where the union of an egg and sperm is made and immediately aborted, many times even without the knowledge of the woman because of an anamoly.
Now, let's say that anamoly is drugs or pollution. Any pregnacy that makes it to term has made it through the 'spontaneous abortion' barrier because it was a union strong enough to withstand the drug or pollution (or a hundred other factors) present at the time of conception.
I believe this is a continuous 'weeding' process and only the 'strongest' unions survive. I also believe that some retardation at birth is due to causes similar to the one mentioned and the retatded person born was at the bottom limit of the survivability level.
I expect that many of us are 'immune' to many things we would be suprised to learn.
This is a continuous process and if environmental conditions change dramatically , only a small handful of us would survive to pass on those genes.
The total miscarriage risk, starting from fertilization, is extremely high at around 60-80%. By the time you see a heartbeat on an ultrasound at 6 weeks LMP, the risk drops to 5-10%. I think this can be considered "maintenance" more than evolution as it involves the filtering of gross genetic errors.
I guess I go back to the line in "Jurassic Park" where the mathematician says "life finds a way". For example, in advanced countries with declining birth rates, it turns out that the very technology that allows for declining birth rates also allows for directed evolution. Science is unravelling/understanding the genetic code while simultaneously providing a way to control reproduction (eg. IVF with PGD). It's only a matter of time before the two are combined. This was explored in the movie Gattaca and other sci-fi works. In another 50 years, this technology will be available to millions of people and many will find it irresistable when starting a family (imagine almost guaranteeing that your child won't have a chronic disease).
I guess it comes down to a battle between natural evolution and human-directed evolution. Which will win?
They will trace back your X or Y chromosomes to their original "clan", but charges about $300 a chromosome and you have to be of European origin.
Huh?
I thought all would depend upon isolating neanderthal nuclear DNA, a thing which may never happen. However, I wasn't reckoning with the ingenuity of the scientists in the field. There's another way. They have found some few genes which a lot of non-Africans have and which Africans don't. These genes may be the heritage of our interbreeding with not-so-related hominids after the last radiation from the breeding ground.
I'm pinging blam because I know he also likes the idea that the neanderthals are still around -- in us.
Pinged you just now but of course you're already here.
We are you heretic.
No. If the original population has genes A, B, C, D, E, F, and G, and one family decides to leave, and they all have gene D, then wherever they settle, their descendants--the new population--will have gene D, but not the other genes. While the original population still has all the genes represented (unless that family that left represented the only gene D carriers in the population).
Not necessarily. This old "non-African" gene could have originated in Africa, but it might have been a local thing, and was mostly concentrated in the tribes that migrated out. The migrants took it with them before it had a chance to spread throughout Africa.
That's exactly what I'm talking about. Genetic errors caused by (?) something...anything...it shifts the genes. (Ever so slowly)
If mosquitos had gone extinct thousands of years ago, could you today explain the cause/source of Cycle Cell Anemia?
just read euripidies or aeschyulus and you'll find their origin beliefs.
If enough of these "ancient" genes turn up, your explanation is the first to fall.
Thanks for the link. I have always wanted to do that.
Bump!
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