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May 18, 2006
WB: The Wonders of Science
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actually, that headline is severly misleading. The point in question is if or when did humans and chimpanzees diverge, did they mate after a considerable time when they because different species.
Long Split between Species
The researchers, from the Broad Institute of MIT and Harvard, propose that humans and chimpanzees first split up about 10 million years ago. Then, after evolving in different directions for about 4 million years, they got back together for a brief fling that produced a third, hybrid population with characteristics of both lines.
That genetic collaboration then gave rise to two separate branches — one leading to humans and the other to chimps.
Posted by: fauxreal | May 18 2006 20:32 utc | 1
Hum. If I had time I’d hunt down the paper and find out what they actually said. As for “viewing each other as appropriate mates”, well. Let’s just say that only one species has to view the other as appropriate…
I’m not sure what information one can really extract from the human genome after the alleged bottleneck it went through a while ago. I rather suspect that the picture from that paper is the tip of a much, much more complicated iceberg.
uh, that should have read “after they became different species.”
the articles for public consumption don’t delineate between Pan paniscus (bonobos) or Pan troglodytes (common chimpanzee) species. I don’t know if it makes a difference…if the assumption is that the Pan genus diverged long after ancestral homonids.
but if you look at “Lucy” homonid representations…however true they may be…the genus differentiation isn’t as pronounced. and there were so many hominid species that are now extinct…or assimiliated, who knows.
pan paniscus, as we’ve discussed around these parts before, have a very different culture than common chimps, and, supposedly, they share more dna with humans than common chimps too.
I think the assumption that homonids were out on the savannah so often is maybe too broad. “Lucy” has feet that can balance on tree branches and graze for fruit. not as easily as chimp feet, of course. maybe they met at the edge of the savannah for a while…but there’s also an interesting question about speciation here…
how many genetic mutations/adaptations does one species have to go through before they make “mules” or make nothing but a mess?
but, yes, the bottleneck and punctuated equilibrium coming out of severe habitat selection pressures could maybe mean that the commonality is somewhere else along the line, maybe?
Posted by: fauxreal | May 19 2006 17:40 utc | 3
oh, and Colman, the WaPo article notes that the part of the genome they’re looking at is female XX.
On Speciation
“This is contributing to the idea that species are kind of fuzzy. They become real over time, but it takes millions of years,” said James Mallet, a geneticist at University College London who was not involved in the new research. “We probably had a bit of a messy origin.”
But not necessarily basing this idea on neo-Darwinian adaptations to the theory of natural selection (i.e. puncutated equilibrium)
The separation into two species “left a footprint on our genome that we can go back and read,” said Eric S. Lander of MIT. “We were never able to look at things like this before. What we need to do now is to collect more data and look for other smoking guns.”
Humans have 23 pairs of chromosomes that contain about 30,000 genes. Each gene is made of strands of DNA “letters” in a specific order, and the letters can change, by mutation, over time. The rate at which changes occur is fairly constant — and very slow.
As a result, genetic mutations can be used as a kind of evolutionary clock. The number of DNA differences between two species’ versions of the same gene is an indication of how long the species have been separate — how long since individuals were last interbreeding and sharing genes.
The loci of the genome comparison-
When Nick Patterson of MIT and his colleagues at the Broad Institute compared the genes of humans and chimps, they found that one of the chromosomes — the female sex chromosome X — was 1.2 million years younger than the others. It appeared the two species shared a common ancestor who gave them both their X chromosomes, and did so more recently than the ancestors who gave them all the other chromosomes.
[and this was in comparison to other primate species, closely and not closely related.]
The best explanation, the scientists think, is that ancient humans and chimps broke away from each other not once, but twice. The first time was more than 6.3 million years ago. The second time was at least a million years later.
but this time frame has always been fuzzy. approximately 5 mil. years is the one I always hear generalized.
…and then there’s the 40 million year ago time that’s hard to find in fossil evidence and the issue of carbon dating from then…maybe these problems have been solved, I don’t know.
Posted by: fauxreal | May 19 2006 19:08 utc | 4
When Nick Patterson of MIT and his colleagues at the Broad Institute compared the genes of humans and chimps, they found that one of the chromosomes — the female sex chromosome X — was 1.2 million years younger than the others.
I knew women just love gorrillas :-/snark
b- gorillas are all talk…or actually all flailing arms and fights with other males. they have penises the size of doorknobs and take a few seconds to ejaculate (like common chimps)
–I think the human female did a great job selecting for males that have at least a 50/50 chance of finding the g-spot, until they were able to read The Guide to Getting It On.
My guess is that that female was minding her own business, bent over washing fruit off in the lake, and a chimp just could resist…
Posted by: fauxreal | May 20 2006 15:18 utc | 7
wait, doorknob wasn’t the idea…I meant the little knobs on kitchen cabinet doors…
sorry, must be scientifically concise when comparing ape anatomy to kitchen decor.
Posted by: fauxreal | May 20 2006 15:19 utc | 8