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."
As far as your link goes, it seems to be a refutation of YECs' vesion of a global flood. The main points they make would not apply to the event I have in mind. Nor would it apply to the findings of Dr. Ross, who holds that the flood covered 'the whole Earth' as understood by the authors, IE- a regional rather than global flood. I don't hold to that myself. There is various evidence for world wide flooding at several points in the past, 12.5 K back, and 28 K back being the dates that I recall.
Perhaps someday I will get around to posting some of those sources. I am buried right now. The short answer is that the evidence for Noah's flood, while not overwhelming, is far greater than zilch.
I don't know this. I don't think anyone does. The geneologies are compressed. The word often translated "became the father of" often does not mean the immediate father, but as one who "started a line leading too". In some places we have "S became the father of Z" while in another place it is clear that S is the great great-grandfather of Z, for they mention T,U,V and the rest coming inbetween.
Maybe they could be streched from 5K back (as a noncompressed reading would show), to 50K back, but I can't see it going any further. If the first humans really did walk the Earth 200K back, it is a death blow to bibical creationism, IMHO.
Biblical Creationism has already been dealt several death blows. It's quite dead but to the mindless folks who still accept it
Any specific reason why you insult without being insulted, as a Christian, I mean?
As a person who spent much of his time dealing with phenomenon at the cellular molecular level, I will tell you that there is still plenty of room for a special creation. Howevere, evolution and creation are NOT as cut and dried as either side would like you to believe. Don't be too dogmatic. The "need" to be right is strong, but sometimes we have to accept that fact that we could be partly or wholely wrong
Since you have some experience in molecular biology, I ask if you would give me your opinion on the arguments presented in the link I gave on post #20?
Am I wrong in considering that the outcome of the statistical study here, neither determines the method nor the agency producing the statistical difference? In fact, the result would be consistent with the viewpoint of an engineering cell.
Interesting article. I think the author makes some very good points. The way the data was presented in the article makes it pretty clear that humans, at least chemically, trace their roots back no more than 50,000 years. I personally do not see how this position has to conflict with evolution or creation - it's what happpened before that seems to have everyone so upset.
No. Rather, I'd be curious to find out exactly why and how W. uses this colloquialism.
Basically the paper begins by saying that change in structures is not neutral (neutral theory) but hase a tendency to "good mutations" (25% they say) and that changes are therefore not all random, that there are "competitive pressures" and "natural selections." "Darwinian forces" are running at about 25%.
How is this any different that Herodotus, who thinking about why the Greeks ("the fittest") beat ("natural selection") the Persians ("flawed") figured that whoever wins ("good mutation") a war ("competitive pressure") has the gods ("Darwinian forces") on its side?
In a single act, such as a battle, large groups of individuals with roughly the same genetic composition are reduced overall. The winners perpetuate, without clear indication that a genetic difference led the Greeks to success or that a genetic difference can be observed in the population after the battle.
There are schools of social Darwinism that, of course, propose that human behavior can be explained in Darwinian terms. The success of a war is dependent on a variety of factors which are not selectable, for example, the hatred between the Greeks and the Persians. What it comes down to, really, is that the ability to wage war at all can be selected for in Darwinian terms. Both Herodotus and the Persians had the gods on their side.
Yet any break from this exclusive use does not commit us to a theory of social Darwinism, even if some have tried to apply the principles of genetic selection to human choice and the complex context of human praxeology. I give the comparison simply to point out that the attribution of success requires more than pointing out the single act of a de facto survivor. Measures of sufficiency, fitness value, and the success of adaptive changes in terms of functionality does not give much new information beyond the mere change that has been observed. In light of that, I find some sympathy for the smart aleck who replied, "duh!" although I do hope the poster has read his Hume.
Wrong, not so much for the consideration, but in the event that you should make such a claim. For it appears that the agency has been clearly determined as "darwinian forces" and the method was mentioned as a "mathematical framework" If I read it again, I should find some more verbiage to that effect.
Of course. (The 'duh!' was inappropriately placed.) This study measures the difference between adaptive survivors and survivors in general.
Measures of sufficiency, fitness value, and the success of adaptive changes in terms of functionality does not give much new information beyond the mere change that has been observed. In light of that, I find some sympathy for the smart aleck who replied, "duh!" although I do hope the poster has read his Hume.
Substitutions or changes in amino acids which confer a functional change on the protein are considered adaptive if they accumulate in the population faster than changes which confer no functional effects. Deleterious changes are quickly deleted from a population and neutral changes are carried along without special advantage. This isn't simply measuring functional changes which survive. This is measuring changes which spread faster through the population than all other changes which survive. By definition these confer a selective advantage.
I just realized that you probably mean the procedure of genetic selection itself. Nothing needs to be said about that if they merely want to point out that a certain percentage (25) subject to the procedure are adaptive and functional in that they take off in "rapid evolutioin" or "accumulate in the population" (pace Nebullis) Whether that index yields the only natural fitness value we will leave ot Max Weber to sort out.
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