Posted on 02/27/2002 1:34:30 PM PST by Nebullis
Researchers from the University of Chicago have demonstrated that natural selection plays a much larger role in molecular evolution than anyone suspected. Their report, published in the February 28 issue of Nature, shows that about 25 percent of genes are evolving rapidly in response to competitive pressures. A second paper in the same issue confirms this discovery.
Although these papers focus on fruit flies, a previous report from the Chicago authors found a similar role for positive and negative selection on the human genome. Data from the previous study (Genetics July 2001) allowed them to estimate the number of fixed "good" mutations, which distinguish humans from monkeys, and the number of residual "bad" mutations, genetic flaws that have piled up in the genome and are slowly being eliminated.
These papers directly conflict with the "neutral theory," which has dominated genetic research since the 1960s. According to the neutral theory, many small genetic changes randomly occur, but the vast majority simply don't matter. Fewer than one percent make enough of a difference that they are either embraced or expunged by natural selection.
"For several decades, the neutral theory has dominated thinking about evolution, but we haven't had the technology to test it," said Chung-I Wu, Ph.D., professor and chairman of ecology and evolution the University of Chicago and director of the study. "Now we are finding that, contrary to this accepted theory, Darwinian forces play a dominant role."
To measure the importance of selection at the genetic level, Wu and his former graduate students Justin Fay, Ph.D., and Gerald Wyckoff, Ph.D., tallied the minute variations within each of 45 genes among flies of one species (Drosophila melanogaster) and contrasted them with the same genes from a different species (Drosophila simulans).
They found that competitive pressures were shaping about one out of four genes. Thirty-four of the 45 genes, or about 75 percent, showed no sign of natural selection. But, 11 genes, or about 25 percent showed evidence of ongoing rapid evolution. These genes contribute disproportionately to the total number of changes, says Wu.
Most of these genes, note the authors, are involved in processes such as disease resistance or sexual reproduction, areas where there is "continually room for improvement."
By studying variation within human genes and comparing them with genes from old-world monkeys, Wu's team has found that the survival of the fittest is just as active in humans.
By comparing variation within the human genome and divergence from our ape ancestors, the researchers determined that about 35 percent of the accumulated changes were "good."
"The proportion is shockingly high," said Wu, "for someone like myself who grew up in the neutralist era." It means one advantageous substitution has entered the human genome every two centuries since humans separated from monkeys 30 million years ago.
"Humans are getting better," Wu added, "but nobody is perfect." Thirty to 40 percent of amino acid changes in human populations, the researchers report, are in fact slightly deleterious. They estimate that the average human carries about 500 harmful mutations, which are destined to be removed from the population by natural selection, but "transiently pile up before their exit."
The assembly of fruit flies, the Nature paper shows, is no less shoddy.
These papers do not mean the end of the neutral theory, cautions Wu. But evolutionary geneticists familiar with the work expect these to be the first of a long string of papers that will rigorously test the theory and determine how much of existing genetic variation matters in the competition for survival.
The neutral theory, proposed by geneticist Motoo Kimura in 1968, was initially controversial but slowly gained near-gospel status. Before the advent of modern genetics, people studied evolution by looking at observable differences -- such as variation in the shape of a bird's beak -- with a clear fitness value. In the 60s, researchers realized that underneath the few obvious differences between related species there were millions of DNA variations, far too many for natural selection to sort out.
So Kimura developed a mathematical framework to explain how evolution worked at the genetic level. He argued that the great bulk of DNA changes were neutral, biologically insignificant consequences of random mutation, and seldom if ever driven by natural selection.
"It was a simple, elegant, beautiful theory," said Wu, "a nice, clean hypothesis that enabled us to make and test predictions based on statistical probabilities. But we are now reminded that biology is by nature very messy, a historical process that generates variety and accumulates multiple tiny aberrations to cope with changing environments."
"These papers tell us how imperfect our genomes really are," said Wu. "At the same time, they tell us how much improvement we have constantly been making, all by means of natural selection."
What? Does this mean that God created man imperfectly?!!!
How do I get added to this list?
And that makes you a ...?
Anyhow, I'm relieved to understand from your post that even some knee-jerk "Intelligent Designists" believe that humans have and continue to evolve!
"The proportion is shockingly high," said Wu, "for someone like myself who grew up in the neutralist era." It means one advantageous substitution has entered the human genome every two centuries since humans separated from monkeys 30 million years ago.
Doesn't this set off any alarm bells for my evolutionary friends? What advantagoues substitutions can be documented as occuring throughout the entire human genome within human history? Didn't "Ice Man" in the Apls and the "Cheddar Man" in England have the same genes as people living in those areas do today?
So you have an "incrediabley high rate" of good mutations separating us from monkies, but almost no change from the earlylist humna DNA that can be found. Also, it is well documented that humans have a remarkable low level of genetic diversity. Two chimps living on the same mountain in Africa can have more genetic diversity than any two people on Earth.
All of that evidence just does not fit with the results of this study- if man evolved from a non-human ancestor. OTOH, if you believe that man was a relatively recent special creation of God then it would be the result that you would expect. A low diversity in the human group, yet a large number of good gene differences from monkies. Far too many good differnces to have accumulated by chance or any other documented evolutiuonary mechanism. The number is especially TOO LARGE when one considers how similiar we are with ancient DNA from bronze age humans. We have not changes harldy a bit in 5K years, but changes must occur rapidly to allow for our differneces with monkies! Special Creation eliminates the contradiction, for only the assumption that we evolved from a common ancestor with monkies produces the contradiction.
Just guessing, but I'd think that an experiment that sought to determine the rate of genetic mutation wouldn't deliberately use a tool universally known to change the rate of genetic mutation.
But I'm just guessing.
The article states a rate of gene change in humans at 1 adventagious substitution every 2 centuries. Considering the number of human genes, and the difficulting in completly mapping the entire human genome, an "Ice Man" would have so few differences that I'd be surprized if any were detected.
I see no inconsistency between this article and evidence previously found.
If the mechanisms for change remain constant, why can't we extrapolate backwards 3 or 4 time periods and conclude somewhere in the distant past all of our genes were slightly "deleterious"? And if we can't do that why should we expect an "improvement"?
Chimps have been where they are in their little local groups about 4 or 5 million years. They even have a subspecies--the bonobos. Humans show "founder effect," the genetic bottleneck of descent from a small group's radiative migration from East Africa perhaps 200k years ago.
You have cited evidence for an already commonly held idea.
It doesn't set off alarms because Ice-Man, or "Otzi," is about 5300 years old. By Dr. Wu's reckoning, that's 25 or 30 advantageous mutations, well within normal variation in human genomes. "Cheddar Man" isn't even that old.
How many mutations does Dr. Wu count since the line leading to monkeys and humans bifurcated?
Duh
Permit me to attempt to make my point again-by the numbers. At the rate given in the article (one good change every 2 centuries, 25%-35% of all changes are 'good') we should have 25 or 26 POSITIVE genetic changes out of a total of 80-100 changes as compared to the ICE and CHEDDAR men. While it is true we did not look over the whole map, we did look in some likely spots and little change of any kind was found, zero positive change.
These are not just good gene changes that some small population has, but gene changes that have worked their way into the whole population. If it has really been 200,000 years since the first humans, we should see 1,000 good gene changes. Not just 'good' in a disease resistance sense, but 'good' as in making us more to the human ideal as compared to the monkey ideal, since that is what is meant by 'good' in the article.
What are the odds that none of the 25 since Ice Man, and none of the 1,000 since First Man, have been 'caught in the act' of spreading throughout our genome? That is to say, none of those genes that make us 'more human' and 'less monkey' are found in some groups, but not yet in others. Why haven't we found such genes? We have looked at the human genome quite a bit, especially sensitive areas have been picked over time and time again. Why haven't we caught some of these genes in the act of spreading? This is another side of the same coin I produce when I say "why are we all so alike if positive changes must occur rapidly and as a huge proportion of the total changes to make us go from monkey to human?"
Humans show "founder effect," the genetic bottleneck of descent from a small group's radiative migration from East Africa perhaps 200k years ago.
Perhaps 200K years ago, perhaps less. Remember this one? 200K is a MAXIMUM value, it could be a lot less. And the bottleneck you speak of has many possible causes, some of which support the creationist viewpoint.
The lack of genentic diversity is real. The belief that mankind is 200K old with a later bottleneck is an INTERPRETATION of that real lack of diversity. As the thread I linked shows in pretty clear fashion, the 200K number is based on some faulty assumptions that when allowed for push the age of mankind down.
You have cited evidence for an already commonly held idea.
Yes I have, a commonly held idea that fits with some ideas held by me and my fellow creationists (old Earth sytle anyway). This will happen a lot when the opinion one holds fits with the facts.
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