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The history of life on Earth has been marked by the evolution of new genes—humans clearly have more genes with more diverse functions than do amoebas. So where do these additional genes, with their new roles, come from? Analysis of genomes shows that the duplication and modification of existing genes seems to be a major avenue for such innovation.
Conventional wisdom had it that duplicate genes provide raw material for evolution. The original gene continues to do its job, whereas the other copy is free to evolve in a different direction.
For example, the venomous cocktail delivered by a platypus's spurs includes three peptides remarkably similar to an antimicrobial compound used in the critter's immune system. The venom molecules evolved from duplications of the gene that codes for an immune compound. Scientists refer to groups of similar genes with different functions as families. Humans carry duplications, too—a group of molecules in the back of the eye that react to incoming photons of light hail from the family of opsin genes. Duplicate genes in the human genome were likely key during divergence from our common ancestry with chimps.
The idea that gene duplication could result in genes with new functions has been around for awhile. Geneticist Susumu Ohno explained the theory in detail in 1970. He argued that duplication is the most important evolutionary force—more powerful than genetic drift, for example. Scientists are still working out the specifics because the vast majority of mutations eventually arising in the duplicates are harmful, meaning they result in function loss; the duplicates would need to stick around for generations before acquiring helpful mutations. But the model required that natural selection should spare the extra gene copies until they had a chance to change for the better.
This problem bothered Dan Andersson, a microbiologist at Uppsala University in Sweden, and John Roth, a geneticist at the University of California, Davis. To better explain how new genes could evolve they suggested a modification of the old model: instead of waiting around for a beneficial mutation, perhaps the beneficial mutation comes first.
This model takes note of the fact that many genes do their primary job of coding for a particular protein very well, but also have a weak secondary function that may become important under certain environmental stressors. For example, one gene might code for a protein that helps bacteria gobble glucose, but also allows the bacteria to snack on starchy cellulose. If all sugar disappears from its environment and only cellulose remains, the bacteria that have this gene will have the capacity to eat more cellulose and therefore be selected for over time and endure. Andersson and Roth's model posited that beneficial mutations already present by chance would be favored by natural selection and stick around in the genome. When the gene is amplified through the duplication, the extra copies give rise to new genes that are better at performing the secondary function, thereby making it prime. "The key is that it never goes off selection," Roth says.
In a study in the journal Science, Andersson, Roth and their colleagues demonstrate the process in lab-grown Salmonella enterica. They grew one strain missing a gene key for expressing the essential amino acid tryptophan. The strain needed to rely on another gene, which had a primary job but also a weak ability to take on the missing gene's work. The researchers encouraged the bacteria to duplicate the overworked gene, and its copies gathered mutations—some of which enhanced tryptophan production. At the end of a year's time (3,000 generations later) the bacteria had one gene that did the original job and a second that had evolved a new primary function—manufacturing tryptophan.
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13 Comments
Add CommentRe: "...[T]he venomous cocktail delivered by a platypus's spurs includes three peptides remarkably similar to an antimicrobial compound used in the critter's immune system. The venom molecules evolved from duplications of the gene that codes for an immune compound."
Reply | Report Abuse | Link to thisSince no human observer was present for the origin of the platypus, what is the evidence that evolution produced these molecules?
Following the hyperlink, “evolved from duplications of the gene that codes for an immune compound,” provides access to the abstract which contains little more than the same assertion quoted above. The paper is only available at unacceptable cost.
@Bill_Crofut
Reply | Report Abuse | Link to thisWe don't need to personally be somewhere during the event in order to observe something. I sincerely hope you're not arguing otherwise.
I would wager the evidence is that there was an obvious gene duplication (homolog), the fact that there's a utility to the gene suggests differential fitness in a population where only some members have it expressed. That's all we need; a heritable change producing differential fitness. That's evolution.
nmlevesque,
Reply | Report Abuse | Link to thisThat is precisely my argument. Please explain to me how one can observe something in absentia.
Wagers and suggestions are not evidence. Is that the basis for evolution?
Natural selection resulted in a net loss of old information.
Reply | Report Abuse | Link to thisOf which I am aware, no spontaneous examples of beneficial mutation have ever been witnessed, above and beyond the deletion of old traits.
Reply | Report Abuse | Link to thisThe evolutionist worldview, itself, is arguably based on religious prejudices from the pagan mystery schools.
For future reference, Christians have no ostensible problem with the operational sciences, but I have no idea why this article was linked on a Christian site, without any provisos.
@Bill_Crofut
Reply | Report Abuse | Link to thisDear Bill, the article you have commented is actually about the direct observation in laboratory of this mechanism of evolution from a duplicate gene. So the mechanism that was guessed figured out for the platypus from indirect evidences has been observed in an experiment. That's how science progress: look at things, guess how it works. Search for another way to verify.
pddelugas,
Reply | Report Abuse | Link to thisThe experiment (p. 1, last para.) doesn't seem to me to be describing any observation of evolution in any meaningful sense of the term (a naturalistic occurrence). Rather, it seems to be describing the observation of a number of laboratory manipulations. Is my assessment incorrect?
Activation of the hyperlink, "team published their results" (p. 2, para. 1) provides an abstract, http://www.sciencemag.org/content/338/6105/384.abstract,
which doesn't seem particularly informative.
The complete paper is only available at unacceptable cost:
http://www.sciencemag.org/cgi/secure_ppv?jcode=sci&resource_id=sci;338/6105/384&type=ppv&ppv_type=article&url=http%3A%2F%2Fwww.sciencemag.org%2Fcontent%2F338%2F6105%2F384.full
boletusp20,
Reply | Report Abuse | Link to thisRegarding your comment 'no spontaneous examples of beneficial mutation have ever been witnessed'. The following article was recently published in Nature:
Blount, Z. D., J. E. Barrick, C. J. Davidson, and R. E. Lenski. 2012. Genomic analysis of a key innovation in an experimental Escherichia coli population. Nature 489:513-518
The authors applied selection to bacterial populations and observed evolution of novel function (i.e a beneficial mutation) that allowed them to metabolize citrate. The bacteria that gained this function became dominant in the bacterial population after a couple thousand generations. The authors can point exactly to the beneficial mutations that allowed this change.
Regarding your comment 'The evolutionist worldview, itself, is arguably based on religious prejudices from the pagan mystery schools'; this is a very big claim to casually throw out there without any support (I'm guessing you are trying to make the connection that evolution is somehow just another religious belief). I'll make an equally big claim that most evolutionary biologists have never heard nor thought about pagan mystery schools when formulating their 'worldviews'.
Bill_Crofut,
Reply | Report Abuse | Link to thisRE: 'Since no human observer was present for the origin of the platypus, what is the evidence that evolution produced these molecules?'
This is a very vague argument that could apply to any intellectual endeavor that attempts to understand phenomena that occurred before humans started keeping records. For instance, no humans were around to observe the origin of Hawaii, so what is the evidence that geological processes produced these islands? This question is only a problem for people who do not understand geology, just as your question is only a problem for people who do not understand evolution.
pjmtele,
Reply | Report Abuse | Link to thisSince no human observers were present to witness the origin of Hawaii, the evidence that is observable concerning that origin must be interpreted. Are you aware of any interpretation that is testable?
Regarding evolution, it seems my inability to understand it puts me in some impressive company with at least one pair of evolutionary biologists:
"Our theory of evolution has become, as [philosopher of science, Karl R.] Popper described, one which cannot be refuted by any possible observations. Every conceivable observation can be fitted into it. It is thus 'outside of empirical science' but not necessarily false. No one can think of ways in which to test it. Ideas either without basis or based on a few laboratory experiments carried out in extremely simplified systems have attained currency far beyond their validity. They have become part of an evolutionary dogma accepted by most of us as part of our training. The cure seems to us not to be a discarding of the modern synthesis of evolutionary theory, but more skepticism about many of its tenets."
[L. C. Birch and Paul Ehrlich. 1967. Evolutionary History and Population Biology. NATURE, vol. 214, p. 352]
Bill_Crofut,
Reply | Report Abuse | Link to thisI replied to your first post because the question you are asking regarding evidence that evolution produces molecules is 1.) poorly stated and 2.) way too big of a question for this forum. If you truly want an answer to that question, you need to start with an introductory class in evolution not an online comments thread. I'm not getting dragged into a long debate because it is clear that you don't actually want answers to these questions. You are simply asking vague, broad questions to try to stump random people on the internet in hopes of validating your own views. And, you're not really in good company by failing to understand evolution. The article you cited is 45 years old, and the authors weren't even evolutionary biologists (they were ecologists). Also, they don't even suggest discarding the modern synthesis of evolutionary theory, only skepticism, which has largely been rebuked over the past 45 years. I'll let you have the last word because nothing I can say could possibly make a difference.
pjmtele,
Reply | Report Abuse | Link to thisPlease accept my apology for asking a question that is too big for this forum. A suggestion made to me by a commentor on another web page was to study a text book on evolution. My request for a recommendation was not answered by the commentator to whom it was directed, but was answered by another:
“@Bill_Crofut–I believe that most textbooks used for the college level would be sufficient to answer your questions. A textbook used at my university is:
http://www.amazon.com/Evolution-Mark-Ridley/dp/1405103450/ref=cm_lmf_tit_2
Evolution, Mark Ridley (Author)”
Is that what you have in mind?
Regarding the age of the Birch/Ehrlich quote, here’s one from Prof. Richard Lewontin that is more timely:
“Our willingness to accept scientific claims that are against common sense is the key to an understanding of the real struggle between science and the supernatural. We take the side of science in spite of the patent absurdity of some of its constructs, in spite of its failure to fulfill many of its extravagant promises of health and life, in spite of the tolerance of the scientific community for unsubstantiated just-so stories, because we have a prior commitment, a commitment to materialism. It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counter-intuitive, no matter how mystifying to the uninitiated. Moreover, that materialism is absolute, for we cannot allow a Divine Foot in the door. The eminent Kant scholar Lewis Beck used to say that anyone who could believe in God could believe in anything. To appeal to an omnipotent deity is to allow that at any moment the regularities of nature may be ruptured, that miracles may happen.”
[1997. Billions and Billions of Demons. NY Times Book Reviews: The Demon-Haunted World: Science as a Candle in the Dark by Carl Sagan, Random House, January 9, http://www.drjbloom.com/Public%20files/Lewontin_Review.htm
Well there is much more evidence of how islands such as hawaii are formed, those structures such as volcanoes are around and we can observe them now. As for the evolution theory, there isnt very much we can go off of to prove evolution, and in my opinion there are many more things to disprove it. For one thing if we have evolved from monkeys why havent monkeys evolved, why are they not all humans.
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