Better late than never

Alfred Russel Wallace One hundred and fifty years ago, British naturalist Alfred Russel Wallace wrote an essay describing some of his ideas on the origin of new species and survival of the fittest species in an environment. Knowing that Charles Darwin had been kicking around some similar ideas, Wallace sent him a copy so the two might compare notes. Darwin, who indeed had for

By | December 1, 2008

<figcaption>Alfred Russel Wallace</figcaption>
Alfred Russel Wallace

One hundred and fifty years ago, British naturalist Alfred Russel Wallace wrote an essay describing some of his ideas on the origin of new species and survival of the fittest species in an environment. Knowing that Charles Darwin had been kicking around some similar ideas, Wallace sent him a copy so the two might compare notes. Darwin, who indeed had formed some seemingly identical conclusions to Wallace's, asked close friend and prominent geologist of the time, Charles Lyell, for advice on how to deal with the similar theories. Lyell suggested that Darwin and Wallace's findings be presented together at the annual meeting of the Linnean Society, held that July in London.

Since that famed, side-by-side presentation of the two naturalists' theories and Darwin's subsequent publishing of On the Origin of Species, Wallace's views have, for the most part, been deemed synonymous with Darwin's. And attribution to the founding theories of evolution has, on the whole, gone to Darwin. A small phrase in Wallace's original essay, however, was his alone: He suggested that certain organisms, or systems that make up organisms, have evolved a way to direct the course of their own evolution, rather than be purely subject to natural selection. As a result, this mechanism could affect whether traits ever get expressed, and therefore subjected to the forces of natural selection. Now, a century-and-a-half later, a group of Princeton University researchers say they're the first to provide evidence to support Wallace's claim.

In 2000, two biochemistry researchers, George McLendon and Stacey Springs, were investigating the proteins that constitute the electron transport chain (ETC). An ancient chain of protein interactions in the mitochondria, the ETC is responsible for passing electrons derived from metabolic sources (food) from one protein to another in a series of redox reactions. As a result of this electron hot-potato, certain proteins release protons into the mitochondrial membrane, creating an unbalanced gradient of protons between the membrane and inner mitochondrial matrix. When enough protons build up, a channel opens on the membrane, and protons stream into the matrix, simultaneously providing the energy to form ATP.

The Princeton group was looking at the molecular mechanism of each protein in the ETC chain. To do so, the researchers mutated each protein's structure one by one, and watched how well the protein was able to transfer electrons, measured as the redox potential in millivolts (mV).

When McLendon mapped the redox potential measurements after each mutation, he saw a striking pattern. Typical redox potentials for each wild-type protein range from -8mV to about 130mV. But regardless of each protein's redox potential in its wild-type version, all mutated versions shot up to around +150mV. This was not a random response, the authors reasoned.

Not sure what to make of the results, McLendon brought a figure illustrating the reactions to Herschel Rabitz, professor of chemistry at Princeton. "McLendon showed me that figure and I said, 'Oh my god, is this true?'" says Rabitz.

Recruiting chemistry research scholar Raj Chakrabarti, the two went about mathematically proving that the ETC proteins were operating under some kind of internal control, suggesting an evolutionary mechanism (Phys Rev Lett, 100:258103, 2008). "The ETC is evolutionarily conserved among all organisms," says Chakrabarti. "There are various variations in terms of exact structure of proteins, but it's one of the most conserved biochemical networks, the base of metabolism." This study was conducted in vitro, so it's not clear whether the mutations disable the ETC, and what influence that disabling might have on redox potentials. But Chakrabarti and his colleagues suggest the ETC has evolved an intolerance to certain mutations that acts as an internal mechanism to control its evolution—hello, Wallace.

"Our work is a piece of evidence that says Wallace's theory was not exactly identical to Darwin's—he had this additional component," says Chakrabarti. The researchers assume that a redox potential of +150mV represents some kind of maximum level. But even if such values derail the ability of the ETC to produce ATP, the theory is still valid, says Chakrabarti: Whatever results the team sees in vivo, an evolutionary mechanism that pushes the redox values to an extreme with every mutation has never been seen before. "Now the next question becomes: How did nature actually do this?" says Chakrabarti.

Update: This article was changed on 12/03/08 to reflect that Alfred Russel Wallace was never knighted, as the original image caption indicated, and that Wallace wrote his essay on evolution before it was presented in July, 1858.


Avatar of: Bill Wallace

Bill Wallace

Posts: 1

December 2, 2008

My Great Grandfather received many awards for his work but was never knighted, although he should have been for what he gave the world! Also I would like to point out his paper outlining the theory of Evolution was presented 1 July 1858.\n\nFor those with the desire to find out the facts behind the publication of the Theory, Wallace's story is a good read. There are some who suggest that Darwin may have not understood the mechanisms of Evolution until Wallace sent him the complete Theory, which Darwin may have used to complete his own... \n\nI have read a number of the works of ARW. Although they are over 100 years old his many ideas are as fresh today as when they were published. It's good to see he's not been forgotten.\n\nBill Wallace\n\n

December 3, 2008

Thanks, Bill Wallace, for pointing out that Alfred Russel Wallace was never knighted. We've corrected the image caption to reflect that. Also, we changed the wording in the first line of the story. The article was always correct in saying that the paper was originally presented in July 1858, it just incorrectly referred to when Wallace wrote his essay on evolution in the first line. We regret the error.\n\nThanks for reading!\n\nAndrea Gawrylewski\nAssociate Editor\nThe Scientist
Avatar of: Daniel Gaston

Daniel Gaston

Posts: 3

December 19, 2008

I first read about this study and paper elsewhere about a month ago, andf found much of the reporting on it, like this one, very misleading and overhyped. This does not look, to me, and I think many others, like any sort of "new" evolutionary mechanism. That the molecular machinery itself would evolve mutational robustness, or in this case intolerance, is an extension of natural selection and not an additional component. \n\nSome others have already blogged on this:\n\nT. Ryan Gregory: \n\n\n\nAnd PZ Meyers:\n\n\n\n
Avatar of: null null

null null

Posts: 44

December 22, 2008

Assuming that mutations stop proton transport at low potentials, and the blockage is always above 150mv, have the researchers checked that it isn't another component of the membrane breaking down at 150mv, conducting and limiting the potential?\nHugh Fletcher
Avatar of: anonymous poster

anonymous poster

Posts: 2

December 22, 2008

"But Chakrabarti and his colleagues suggest the ETC has evolved an intolerance to certain mutations that acts as an internal mechanism to control its evolution?hello, Wallace."\n\nNo, I would say this is yet another example of irreducible complexity - hello Behe.
Avatar of: anonymous poster

anonymous poster

Posts: 6

December 24, 2008

Wallace's letter from Ternate for Darwin was known as Letter From Ternate. That letter became famous because it was included a working paper with a title " On the Tendency of Varieties to Depart Indefinitely from the Original Type ". From that paper, Wallace stated his idea about nature selection process which maintained a species in the world. The species which can survive was called as the result of survival of the fittest. That was the basic outline to understand the nature selection which was put by Wallace at that time. His idea supported evolution theory which was popularized by Darwin in his book " The Origin Of Species " in 1859, a year after the paper writing of Wallace.\nThe Letter From Ternate made Darwin and his friends shock, because Darwin had already involved in the process of natural thinking about nature selection, but they haven't still been able to give the conclusion as clear as Wallace's conclusion about survival of the fittest.\nOn July 1^st,1858, Darwin's friends, Charles Lyell and Joseph Hocker, engineered the scientific meeting in Linnean Society and declared Darwin and Wallace as the founder of basic evolution. But, in the journey of the history, the name of Wallace was forgotten.\nWallace stopped in Ternate ( Indonesia/ Nusantara ), on January 8^th - March 25^th, 1858, when he got malaria and forced himself to write a letter and sent it to Charles Darwin.
Avatar of: Steve Summers

Steve Summers

Posts: 28

January 7, 2009

Harvard School of Public Health scientists John Cairns, Julie Overbaugh, and Stephan Miller in a 1988 Nature paper titled "The Origin of Mutants, made this statement: "We describe here experiments and some circumstantial evidence suggesting that bacteria can choose which mutations they should produce." \n\nThis paper addressed the idea of directing the course of their own evolution in addressing whether "mutations sometimes arise as a specific response to the current needs of an organism."\n\nWhen stressing (rather than imposing lethal selection) Lac- E coli by plating them on an agar substrate with only lactose as an energy source, the bacteria go into the non-dividing, non-replicating starvation "stationary phase." They can and do still mutate. In this case to survive they were obliged to express a specific mutation. Lac+ revertants appeared in a statistical distribution that led Cairns et al to suggest that the bacteria `chose' their mutation.\n\nUniversity of Connecticut's Barry Hall reported in a 1988 Genetics article a follow up experiment in which he introduced a strain of E. coli to a substrate that require two mutations, one exceedingly rare, to utilize salicin. Sal+ revertants appeared in a frequency that was orders of magnitude greater than predicted by classical theory of random mutations. Hall has published several papers that support "Directed Mutation."\n\nOthers experimented and supported or contradicted Cairns' and Hall's results. Other theories offered different explanations and new data were gathered about mutation. One such data was that super-mutating bacteria were more frequent in drug resistant populations (LeClerc et al, Science 274: 1208-1211, 1996). This provided one possible mechanism for "Directed Mutation" as it offered the possibility that some bacteria have evolved the propensity to super-mutate under stress. \n\nThe final outcome, however, so far as when I last looked at it, had not ruled out "Directed Mutation."
Avatar of: Steve Summers

Steve Summers

Posts: 28

January 8, 2009

My title should more accurately have been "Not the first to offer evidence suggesting direction in evolutionary processes." \n\nCarins has called called this "selection-dependent mutation" and the commonly used phenomenon descriptor shifted to "adaptive \nmutation" from "directed mutation." However the use of "directed," or "adaptive," has shifted with many researchers from the mutation to mutagenesis, the process of generating mutations as a functional response to stress -also called hypermutation or transient mutation.\n\nThis is perhaps analogously or metaphorically like a cat thrashing about in a cage until it hits the experimenter's lever that opens the door.\n
Avatar of: anonymous poster

anonymous poster

Posts: 1

January 11, 2009

I don't think that people can mutate something in the laboratory and claim that this is 'evolution'. This is the equivalent of mutating pigeons until they cannot fly and then claiming that this is an exception to evolution or a new type of evolution. Maybe people that work in laboratories need to get out more - into the field maybe...

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