Did humans and chimps once interbreed?

[Woodmonkey]

Did humans and chimps once interbreed?

Tangled family tree

IT GOES to the heart of who we are and where we came from. Our human ancestors were still interbreeding with their chimp cousins long after first splitting from the chimpanzee lineage, a genetic study suggests. Early humans and chimps may even have hybridised completely before diverging a second time. If so, some of the earliest fossils of proto-humans might represent an abortive first attempt to diverge from chimps, rather than being our direct ancestors.

We can observe the traces of this complex history in the human genome today, says David Reich, a population geneticist at the Broad Institute and Harvard University in Cambridge, Massachusetts. Reich and his colleagues compared the genomes of humans, chimps and gorillas using a "molecular clock" to estimate how long ago the three groups diverged. The further back two species diverged, the more differences will have accumulated between their genome sequences.

The team estimated that humans and chimps diverged no more than 6.3 million years ago, and probably less than 5.4 million years ago, although some parts of the genome showed divergence times up to 4 million years older. Even if we split from our ape relatives 6.3 million years ago, that is still later than some of the earliest fossils showing human-like traits such as altered tooth structure and bipedalism (Nature, DOI: 10.1038/nature04789). "That makes the fossil record even more interesting," says Reich. "What were those fossils?"

The answer might lie in a second striking observation. Reich's team found that the X chromosome diverged later than any of the other chromosomes. One way this can arise is if natural selection has been acting unusually strongly on genes on the X chromosome. That is significant because in every animal species studied, genes that make hybrids less fertile than their parental species tend to be found on the X chromosome or its equivalent, so hybridisation can create strong selection pressures on this chromosome.

The best explanation for these surprising findings - the relatively young and variable divergence dates between the human and chimp lineages, and the evidence for strong selection on the X chromosome - would be if the two lineages split sometime before the time of the first proto-human fossils, but later rehybridised (see Diagram) in a "reverse speciation" event (see "When evolution runs backwards"). Natural selection would favour those hybrid individuals whose X chromosomes carried fewest of the genes that lower fertility.

So far, Reich admits, this is only a plausible hypothesis, not a proven fact. For example, he calibrated his molecular clock using the divergence time between humans and macaques, which is estimated at no more than 20 million years ago. If this divergence happened earlier, that would push back the human-chimp split to an earlier date as well - perhaps far enough that there would be no need to invoke hybridisation. At the very least, though, Reich's study shows that the separation between humans and chimps was a long, drawn-out process.

[url=http://www.newscientist.com/article/mg19025525.000?DCMP=NLC-nletter&nsref=mg19025525.000]The Source[/ur]

[DocDiggs]

I read this elsewhere and to get into it here is far too pre-mature. Much more research needs to be done on this as it is in it's very preliminary stages. It's hardly a topic for uninformed opinion.

[Woodmonkey]

Originally Posted by DocDiggs

It's hardly a topic for uninformed opinion.

That's in the eye of the beholder, Doc.

[DocDiggs]

Originally Posted by Woodmonkey

That's in the eye of the beholder, Doc.

I'm speaking professionally as a biologist. If y'all want to beat yourselves silly over this...be my guest. Whatever is said will be blowing in the wind.

[USA11B]

Did humans and chimps once interbreed?
I don't know about interbreed, it appears there has been intercourse.
AIDS traced to African monkeys

Friday, June 13, 2003 Posted: 11:54 AM EDT (1554 GMT)

• Special Report: AIDS

LONDON, England -- An international group of scientists has traced the ancestry of the virus that caused AIDS back to strains found in African monkeys.

Two different monkey virus strains combined in chimpanzees to create the HIV virus which was then passed on to humans, the scientists told the journal Science.

Earlier studies had shown that humans contracted the virus that attacks the immune system from chimps, but were unable to determine where the chimps got the virus from.

More than 25 million people have been killed by the AIDS virus that kills white blood cells and causes the body to become defenceless against infections with an estimated 40 million people living with HIV, according to a report by the U.N. last year.

After analyzing the DNA make-up of the simian immunodeficiency virus (SIV) in African monkeys they found the red-capped mangabeys and spot-nosed guenons carried the strains.

The virus was passed onto chimpanzees when they ate infected monkey meat, believe the scientists from universities in France, America and the UK.

The study was undertaken by scientists from the University of Nottingham, the University of Alabama at Birmingham, Duke University, Tulane University and the University of Montpellier in France.

Troops of chimpanzees -- who are apes -- chase monkeys through forests while others wait in trees to catch the monkeys as they run past. The carcasses are ripped apart and eaten on the spot so blood mixing is possible, one scientist said according to The New York Times.

The new evidence suggests that the viral DNA combined to create a hybrid strain from which HIV can be traced.

How humans contracted the deadly virus remains a mystery although it is believed that it was contracted in the same way as chimps through hunting 'bush meat'.

It is generally believed that a chimpanzee hunter contracted the virus in the early part of the twentieth century by cutting himself while preparing the meat.

The virus then mutated into HIV and was passed through millions of human beings.

"The recombination of these monkey viruses happened in chimpanzees and the chimp transmitted it to humans on at least three occasions," said Frederic Bibollet-Ruche, co-author of the study to The Associated Press.

"The transfer between chimps and humans probably happened before 1930," said Bibollet-Ruche from the University of Alabama, Birmingham.

He believes that monkeys and chimps carry many different strains of SIV viruses that could be spread to humans creating a new world epidemic, reported AP.

The findings show that other primate species can acquire the virus under natural conditions.

Last year French scientist found that one strain of the SIV virus contained a gene that allowed it to pass straight to man from monkeys. The SIV virus does not cause disease in chimps and monkeys.
SOURCE

[Woodmonkey]

Originally Posted by DocDiggs

I'm speaking professionally as a biologist. If y'all want to beat yourselves silly over this...be my guest. Whatever is said will be blowing in the wind.

Doc, why do you judge us when you don't like what we discuss? Are we supposed to get your permission for the threads we start in here?

[DocDiggs]

Originally Posted by Woodmonkey

Doc, why do you judge us when you don't like what we discuss? Are we supposed to get your permission for the threads we start in here?

Dear God, WM!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I am not freaking JUDGING you!!!!!!!!!!!!!!!!!!!!!! Discuss whatever U want. jFar be it feom me to try and sopt anything in here!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! What is your prob? I just don't give a rip! n What is it you dont'comprehend about that? Get over it!