Neutrality in the Matrix

A few days back, I posted this comment on the BioLogos blog:

Wikipedia describes panselectionism as “the idea that selection is the only force strong enough to explain evolution, relaying random drift and mutations to minor roles.”  So where did this bad idea come from?  Let’s just say that I think one can make a reasonable case that panselectionism emerged naturally from the Modern Synthesis (which some people, even today, equate with the “theory of evolution”).

Second, the rise of non-adaptive hypotheses and the decline of panselectionism helps us see the whole junk DNA debate in a more interesting light than the creationist debates – the existence of junk DNA helps to illustrate that natural selection is not always in play during evolution.  Natural selection, which is the only viable designer-mimic, is not omnipresent.

And that leads to the third, and most interesting, point.  If we step back and consider evolution as function to generate more complex life forms, then it’s becoming more clear that the success of evolution is dependent on selection and neutral forces alternatively working in series.  In fact, this is what scientists have also found to be true when it comes to designing new protein activities by using in vitro evolution.  Paradoxically, this means that that if evolution is to spawn something like mammals, it needs to go through phases which suspend the role/reach of natural selection.  Those non-adapative processes, seen in the context of life’s architecture, may be a very clever (and non-intuitive) aspect of a design strategy.  The intelligent use of chance.

Yesterday, I ran across this:

Biologists at the University of Pennsylvania studying the processes of evolution appear to have resolved a longstanding conundrum: How can organisms be robust against the effects of mutations yet simultaneously adaptable when the environment changes?

The short answer, according to University of Pennsylvania biologist Joshua B. Plotkin, is that these two requirements are often not contradictory and that an optimal level of robustness maintains the phenotype in one environment but also allows adaptation to environmental change.

Using an original mathematical model, researchers demonstrated that mutational robustness can either impede or facilitate adaptation depending on the population size, the mutation rate and a measure of the reproductive capabilities of a variety of genotypes, called the fitness landscape. The results provide a quantitative understanding of the relationship between robustness and evolvability, clarify a significant ambiguity in evolutionary theory and should help illuminate outstanding problems in molecular and experimental evolution, evolutionary development and protein engineering.

The key insight behind this counterintuitive finding is that neutral mutations can set the stage for future, beneficial adaptation. Specifically, researchers found that more robust populations are faster to adapt when the effects of neutral and beneficial mutations are intertwined. Neutral mutations do not impact the phenotype, but they may influence the effects of subsequent mutations in beneficial ways.

http://www.sciencedaily.com/releases/2010/01/100120131203.htm

And then there is this:

Everywhere you look in nature, you can see evidence of natural selection at work in the adaptation of species to their environment. Surprisingly though, natural selection may have little role to play in one of the key steps of evolution – the origin of new species. Instead it would appear that speciation is merely an accident of fate.

So, at least, says Mark Pagel, an evolutionary biologist at the University of Reading, UK. If his controversial claim proves correct, then the broad canvas of life – the profusion of beetles and rodents, the dearth of primates, and so on – may have less to do with the guiding hand of natural selection and more to do with evolutionary accident-proneness.

[….]

To Pagel, the implications for speciation are clear: “It isn’t the accumulation of events that causes a speciation, it’s single, rare events falling out of the sky, so to speak. Speciation becomes an arbitrary, happy accident when one of these events happens to you.”

All kinds of rare events could trigger the accident of speciation. Not just physical isolation and major genetic changes, but environmental, genetic and psychological incidents.

http://www.newscientist.com/article/mg20527511.400-accidental-origins-where-species-come-from.html?page=1

I really hope to offer some more substantive commentary on these in the future.

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3 responses to “Neutrality in the Matrix

  1. In the chapter “Two Binding-sites Rule” from his book, The Edge of Evolution, Behe offers his theoretical argument that the most we can expect from unguided evolution — assuming that there are no selective intermediate steps — is producing two binding-sites (three interactive proteins). One of his premises is that neutral mutations would only be able to account for 1/3 of the mutations necessary (based, I think, on a study by Douglas Axe). Is there contrary evidence that neutral mutations account for more than that?

  2. I forgot to include a link to his argument.

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