It doesn't add up

Jun 03, 2011 By B. D. Colen

An important new finding by Harvard researchers indicates that cellular mutations responsible for an organism’s successful adaptation do not, when combined over time, provide as much benefit as they would individually be expected to provide.

The study from the laboratory of Christopher Marx, an associate professor in the Department of Organismic and Evolutionary Biology (OEB), is one of two investigations with identical approaches and equivalent results that are being published in Friday’s (June 3) issue  of the journal Science. The other paper comes from the lab of Tim Cooper, an assistant professor in the University of Houston’s Department of Biology and Biochemistry.

Hsin-Hung Chou, a postdoctoral fellow in Marx’s lab, is the first author on the Harvard paper.

Although the Harvard and Houston groups each studied a different bacterium that evolved in different conditions, the patterns they uncovered were the same: The more fit the strain was before introducing the beneficial mutation in question, the less further improvement was conferred.

Marx and Cooper, who are both colleagues and friends, submitted their work simultaneously to Science this past February, asking that the journal consider their manuscripts jointly. “We independently came to the same remarkable punch line with completely different model systems. We thus feel that this congruence of results adds substantial strength to the suggestion of generality from our findings,” they wrote in their joint submission letter to Science. The two research groups posit that their findings help explain the “deceleration of population adaptation” over time.

Although the papers of Marx and Cooper came to remarkably similar conclusions, they contrasted strongly with analogous studies looking at mutational combinations within single proteins. For example, an earlier paper from the laboratory of Daniel Hartl, Higgins Professor of Biology in OEB, showed that mutations within the enzyme that provides resistance to penicillins interacted with each other violently. The same mutation could be tremendously beneficial if partnered with some mutations, and quite deleterious when grouped with others. These interactions would greatly constrict which paths for improvement can be driven by natural selection.

In their letter to Science, Marx and Cooper wrote that “our papers are critical because they paint … [a] picture that suggests that adaptation involving the wider context of whole genome networks may behave entirely differently than adaptation of proteins.  Interactions between beneficial mutations are common but seldom impose hard limits on the mutational transitions that can be selected. This result has broad implications for understanding the trends and causes of fitness landscapes.

“Any finding in experimental evolution establishes rigorously what can happen; when results are repeated across systems it suggests that this might actually be what does happen in nature.  Indeed, this simple effect of mutation interactions on the form of the fitness landscape may provide a new ‘predictability’ to evolutionary biology,” they wrote.

The editors of Science apparently agreed with Marx and Cooper, and not only are the papers being published in the same issue of the journal, Science is also publishing a commentary on the papers titled “Evolutionary Sum Is Less Than Its Parts.”

Earlier studies of evolutionary mutations in individual proteins, and preliminary studies done in Marx’s lab had shown that mutation was order dependent, that the order of changes over time had a controlling effect upon the end result. “But our work and the other new work being published shows a different picture throughout the cell,” Marx said. “We found that all positive mutations are always good, but the amount that they’re good becomes less and less over generations.”

One of the exciting things about doing this kind of science, Marx said, is that it demonstrates that evolution is something that can be studied with microbes in the laboratory, and on the timeline of a graduate career. This allows questions of broad interest in natural systems to be addressed experimentally.

“Our ultimate goal,” Marx said, “is to find out why this happens. We need to be able to understand these interactions in order ultimately to be able to take advantage of them.”

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whoyagonacal
5 / 5 (4) Jun 03, 2011
WHY do I get the feeling that our resident creationists will proclaiming these fine-print studies as "fatal blow to Darwinism"?
J-n
5 / 5 (4) Jun 03, 2011
to me, this study actually is more in favor of a non-designed model as opposed to one that was designed.

Changes, if designed by a perfect being (god?) should be expected to not only NOT HAPPEN (perfection cannot be improved upon) but if it were to happen should be expected to show significant improvement. If not, then the creator is not perfect.
FrankHerbert
1 / 5 (4) Jun 03, 2011
When was the flood Kevin?
Physmet
4 / 5 (4) Jun 03, 2011
I'm not sure I see negative implications for the concept of evolution. What it sounds like is a decreased return on investment when it comes to beneficial change. If you are already well suited for your environment, a good change is still good, but how much more can you be benefited, since you are already successful? If you already eat your fill and can defend yourself, how much more could an evolutionary change benefit? However, a negative change will have greater impact at that point.

The opposite would also be true. If you are poorly suited for your environment, further negative changes would have smaller impact. You're likely to starve or be eaten anyway, so how much worse will it get?
PaulRC
5 / 5 (2) Jun 03, 2011
sounds to me like their definition of 'most fit' is off. they are describing the 'most fit' as the most successful in the initial environment, and then changing the environment. clearly, in that case, the 'most fit' is the most adaptable organism, not necessarily the one that was the most fit in the previous environment.
the fact that they find a 'law in decreasing returns' isn't that surprising to me.
whoyagonacal
5 / 5 (3) Jun 03, 2011
I'm not sure I see negative implications for the concept of evolution.


Neither do I, but that has never slowed down creationists much.
210
1 / 5 (2) Jun 03, 2011
to me, this study actually is more in favor of a non-designed model as opposed to one that was designed.
Changes, if designed by a perfect being (god?) should be expected to not only NOT HAPPEN (perfection cannot be improved upon) but if it were to happen should be expected to show significant improvement. If not, then the creator is not perfect.

We live on a LIVING planet, hence,"Any finding in experimental evolution establishes rigorously what can happen; when results are repeated across systems it suggests that this might actually be what does happen in nature. Indeed, this simple effect of mutation interactions on the form of the fitness landscape may provide a new predictability to evolutionary biology, they wrote. There is more to evolution than JUST mutation. Life's ability to adapt must help us to write a much more compelling picture of evolution BUt, we did NOt create life, we still cannot define it only describe it THAt is profound!
word-to-ya-muthas
210
1 / 5 (1) Jun 03, 2011
sounds to me like their definition of 'most fit' is off. they are describing the 'most fit' as the most successful in the initial environment, and then changing the environment. clearly, in that case, the 'most fit' is the most adaptable organism, not necessarily the one that was the most fit in the previous environment.
the fact that they find a 'law in decreasing returns' isn't that surprising to me.
That which is most fit in the initial environment CHANGES that environment, they dominate it in many or all ways. As mutation moves into the gene pool, beings fail the fit test, move, OR they pass it and rule a niche in Madagascar, Europe, India, the Artic, etc.It would appear that we must start off with FLAWLESS specimen or the gene pool becomes corrupt too fast: dominant gene flaws doubling through inbreeding in the first 5, 10, 20 generations-if not for some adaptive trigger (environmental or extraterrestrial) AND non-ruinous mutation, life would fail.
word-to-ya-muthas
simplismic
not rated yet Jun 03, 2011
Isn't this just a specific example of the general idea that the sum of 2 orthogonal movements is less than their linear sum? (for equal vectors, the sum is the length times the square root of 2 rather than the length times 2.)
hush1
not rated yet Jun 20, 2011
Well, discourse is good. They have to published. There weren't any PaulRCs around to listen to during their research. The researchers can't anticipate all feedback until publishing.