Scientists sort the chimps from the men

A team of molecular biologists have taken a step towards defining what makes us human. It is not so much our differing gene sequences that distinguish us from our primate cousins, but how active those genes are, the team has discovered.

Chimp and human genomes vary by only 1.3 per cent and only a tiny fraction of this actually affects genes. The new research shows how variation in the amount of product of a gene may be as significant to our recent evolution as structural changes.

The greatest changes in gene expression have been in the brain, say the researchers, perhaps explaining why human mental capabilities have evolved so rapidly.

"This is the first open door to understanding how humans became humans and chimps became chimps," says Wolfgang Enard, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, the study's first author.

"Expression patterns are certainly the key to the differences between chimps and humans," says Chris Stringer of the Natural History Museum in London. "And these changes have been hidden up to now."

But Walter Messier, director of Evolutionary Genomics, Denver, Colorado told New Scientist: "It's sometimes difficult to devise an adequate control when you do expression pattern work. Let's face it, expression patterns can change after one has had lunch, for example. But it is a very valuable approach."

Evolutionary Genomics is trying to identify differences between chimp and human gene sequences, for example in relation to HIV susceptibility.

The new analysis compares gene expression patterns in blood cells, liver and brain tissue from chimps and humans, and also orangutans and monkeys for reference. The researchers used a molecular tool called a DNA chip to detect the products of up to 12,000 active genes.

The greatest variations in gene expression patterns were found in the brain. The researchers estimate that there have been more than five times the number of changes in human brains than chimp brains since their evolutionary lines diverged.

This may explain how humans have developed such unique mental capabilities as language, culture and planning, the researchers say. But changes in gene expression must in the end originate from DNA changes and the researchers do not yet know which groups of genes are responsible.

So far only two genetic differences have been biochemically characterised, one affecting cell surface structure and one that may affect hair structure.

Identifying which genes are responsible could help us to learn more about the genetic basis of diseases, says Enard, if we can correlate gene expression patterns with differences in susceptibility to cancer, Alzheimer's or AIDS.

Finally, Enard cautions: "The question of what makes us human can be answered in so many different ways. Never will molecular biology tell us everything."

This story is from NewScientist.com's news service - for more exclusive news and expert analysis every week subscribe to New Scientist print edition.

Before I call it a night I wanted to get a link to this old but relevant thread up...

Descent of Man Theory: Disproved by Molecular Biology

http://www.FreeRepublic.com/forum/a3b47d7b94f92.htm

Whatever "evolutionary changes" occured in the brains of the human line, humans themselves have a remarkable lack of genetic diversity. IMHO the best interpretation of the evidence presented in the above thread (articles and posts) is that the earliest man appeared 50K ago or less.

Ummm. Let's see. I thought the silent mutation rate was a good measure of how fast something could evolve in a given amount of time. Such mutations may not have natural selection helping to establish them in the population, but they still help establish a baseline for how often a given species has mutations (and thus a chance at developing the super-rare 'helpful mutation').

Let's say one species mutates 10 times faster than the other. Doesn't that mean that it has 10 times the chance to get a NON-SILENT gene change? In other words, measuring silent mutations doesn't measure the etheral "helpful mutation" rate per se, but a species with a higher silent rate will, as I understand the theory, also have a better chance of more "helpful mutations".

Chimps and especially people have a very low mutation rate. So low that even the minor gene differences we see appear to be a lot of change in a little time. I understand a helpful mutation, if it happens, would be selected for, but if genes don't mutate much then a helpful mutation is indeed a rare unicorn. It does not matter that it will be selected for once it arrives, if it rarely arrives then I don't see how you get from A to B in the time allowed.

This is a good example of the difference between what the facts actaully say and what a biased interpretation of those facts leads one to understand. The study pinpointed no such "small mutations (which) lead to a cascade of extragenetic effects." The article specifically states "But changes in gene expression must in the end originate from DNA changes and the researchers do not yet know which groups of genes are responsible."

That clearly means they 1) Don't know what changes in genes are reponsible and 2) Have not established that such mutational changes have a reasonable probability of occuring in the time allowed.

Those things are ASSUMPTIONS by those who take it on Faith that evolution must be true.

Indeed, it has not been demonstrated that there is a 'pathway' of gene changes between the two that is breechable by a series of functional intermediates at all. It may be that Man and Chimps represent two genetic "islands" with no series of genetic steps between them that can produce an unbroken series of functional organisms. Or maybe there is a potential functional pathway, but it the changes are unlikely to have occured by any obserserable evolutionary process in the time allowed since the alledged 'common ancestor'. In any case, even demonstrating such a pathway had a fair chance of producing man is not proof that it DID produce man. That would still be an assumption based on faith. A 'special evolutionary process' as the article says. They cannot describe for us this process, and cannot find where or how it occurs, but the just "know" it was an evolutionary process!

As mutation rates slow down, notice that the correspondence between genotype and phenotype becomes more complex.

I would be interested to know why you think this is. I am guessing that all critters that have a low reproduction rate need a more stable DNA set. Humans and Chimps cannot afford the same mutation rate as mice! I would guess our mutation rate in HOX or whatever controls gene expression would also be lower than that of mice. After all, gene expression errors should be able to produce unfit organsims just as well as regular gene errors.

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