The Scientist
Volume 24 | Issue 1 | Page 24
By Bob Grant
Should Evolutionary Theory Evolve?
Some biologists are calling for a rethink of the rules of evolution.
Evolution, by its very nature, is a dynamic process. But just as fluid are humankind’s efforts to understand, describe, and conceptualize that process. Out went Lamarck, in came Darwin. Mendel’s insights set the rules for genetic inheritance, then certain exceptions to Mendel’s rules materialized. So forth and so on.
The most recent, broadly recognized codification of evolutionary theory is known as the Modern Synthesis. After nearly 3 decades of theorizing, experimentation, and writing by paragons of evolutionary thought—Ronald Fisher, J.B.S. Haldane, and Sewall Wright, to name but a few—British biologist Julian Huxley cemented the term in 1942 with the publication of his book Evolution: The Modern Synthesis. The theoretical framework brought Darwin’s ideas into the 20th century and married them to the gene’s-eye-view of biology that was emerging at the start of the century, with the rediscovery of Gregor Mendel’s inheritance research.
According to the Modern Synthesis, populations containing some level of genetic variation evolve via changes in gene frequency induced mostly by natural selection. Phenotypic changes are gradual, and speciation and diversification into higher taxonomic levels come about over long periods of change. These ideas have remained largely unchallenged for more than a half-century.
But since the 1940s, science’s concept of evolutionary dynamics has, well, evolved. Indeed, these days, calling the Modern Synthesis “modern” might be a stretch.
Some evolutionary biologists say that the body of knowledge concerning evolutionary processes has simply outgrown the confines of the Modern Synthesis, which was crafted before science had a strong grasp of genomics, molecular biology, developmental biology, and other, more recently derived disciplines, such as systems biology.
City University of New York evolutionary biologist and philosopher Massimo Pigliucci insists that expanding evolutionary theory so that it captures recent insights doesn’t mean throwing out 150 years of sound thinking. “We’re not talking a revolution,” he says. “Nobody’s going to deny Darwin and all that stuff. But it has been several decades since the last time evolutionary biologists actually sat around the table, so to speak, and came up with the basic principles of their field.”
In the summer of 2008, Pigliucci and his colleague, University of Zurich researcher Gerd Müller, invited 14 other researchers to the Konrad Lorenz Institute in Altenberg, Austria, near Vienna, to discuss how to rethink the Modern Synthesis. This spring, Müller and Pigliucci plan to publish a tome that arose from the Altenberg meeting, with chapters written by its attendees. It will be titled, Evolution: The Extended Synthesis. “The word ‘extended’ is important because it implies quite clearly that there is no rejection of the previous synthesis,” Pigliucci says. “There is no rejection of the Modern Synthesis. There is no rejection of Darwinism. It’s an extension of it—we think a significant extension in a lot of different directions which neither Darwin nor the Modern Synthesis could have possibly thought of.”
Of course, not all biologists agree. Critics argue, for instance, that the field has been adapting for years, and a handful of new data doesn’t warrant formally expanding a theory that forms the field’s fundamental framework.
To judge for yourself, here are just a few of the concepts that Pigliucci, Müller, and other Altenberg meeting attendees believe evolutionary theory should adapt to include.
Evolvability - What is it
Evolvability, taken simply, means the ability to evolve or to produce heritable, phenotypic variation. Some lineages are suspected to be more evolvable than others, meaning that dramatically different phenotypes—what University of Vienna evolutionary biologist Andreas Wagner calls “game changers”—may arise quicker in these lineages, independent of how much baseline genetic variation is present. In this way, researchers who study evolvability consider it a metaproperty that, itself, can evolve.
Why is the Modern Synthesis lacking?
The Modern Synthesis addresses evolvability in a population genetics sense—some populations have more genetic variation than others and would therefore be expected to generate phenotypic variation at a faster rate. But it does not treat evolvability as a distinct trait of those populations, independent of the underlying genetic variation.
According to Wagner, the Modern Synthesis also fails to adequately conceptualize the major evolutionary milestones (i.e., photosynthesis, flight, multicellularity) that stand out against a backdrop of slow and steady evolution. “You can look at the history of life as the evolution of game-changing innovations,” he says. “If you’re interested in evolutionary innovation, you can’t get away anymore with a very simple, one-dimensional notion of a phenotype. Now we can recognize that there is a deficiency in the Modern Synthesis.”
Where is the evidence?
“There has been a surge in theoretical studies of evolvability, and now we’re beginning to look at some of the first empirical results coming out,” Pigliucci says.
Validating the concept of evolvability hinges on deciphering the mechanism for evolvability’s inheritance. What property might bestow on its holders the ability to evolve at a different speed than other species? One researcher claims to have found an answer. Susan Lindquist, a molecular biologist at the Massachusetts Institute of Technology who specializes in protein folding, says that [PSI+]—a prion that results from the misfolding of the Sup35 protein in the yeast Saccharomyces cerevisiae—may serve as a conduit for the evolution of novel traits and a molecular vehicle for evolvability.
Sup35, the functional domain of which is highly conserved in a variety of organismal groups, normally serves as a translation termination factor. That is, it helps ribosomes recognize stop codons on mRNA and therefore mediates the normal translation of proteins. The misfolded [PSI+] cannot perform this function correctly, and yeast cells containing aggregations of the prion read through about 5 to 10 percent of stop codons in a given cell. This means that cells with [PSI+] could express normally silent sequences beyond the c termini of genes or express different levels of normal proteins, because without a stop codon, mRNA may stick around longer in cells, enabling the cells to express more protein. These cells end up expressing a wide variety of phenotypes that essentially can’t arise in normal cells.
When Lindquist coaxed several genetic strains of S. cerevisiae into carrying [PSI+], then subjected them and genetically identical cells with normal Sup35 to a variety of growth conditions, she saw phenotypic variation in the [PSI+] cells come out of the woodwork.1 In nearly half of the conditions Linquist tested, having [PSI+] led to significant phenotypic effects in some of the strains. [PSI+] was essentially uncovering previously hidden phenotypic variation in the yeast cells, and in some of the conditions to which they were subjected this variation was advantageous.
This means that [PSI+] could act as what Lindquist calls a “capacitor and potentiator” of evolvability, because switching into the [PSI+] state makes a yeast population more likely to produce phenotypic diversity when environmental conditions change.
What’s more, Lindquist showed that the [PSI+] prion can be passed from mother to daughter yeast cells when they divide either mitotically or meiotically. Even if a lineage were to revert back to the non-prion state (which occurs naturally once every 100,000–1,000,000 cell divisions or so, depending on the strain), selection may have fixed the advantageous adaptations that resulted from the [PSI+] read-throughs. Linquist says she’s looking at differences in [PSI+] states among wild fungal populations now.
These results are interesting, but might create few waves in the flow of evolutionary history, says Indiana University evolutionary biologist and population geneticist Michael Lynch. “It’s an observation that if you stress the hell out of an organism, it does weird things,” he said. “There’s no question you get more extreme phenotypes than you would in a benign environment. But there’s no evidence whatsoever that the tendency for organisms to do this kind of thing when they’re stressed is there because natural selection favored it.”
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NOTA TRIUNFANTE DESTE BLOGGER:
Eu sempre afirmo neste blog que eu fico muito feliz quando sou vindicado pelos evolucionistas. Especialmente as publicações de divulgação científica. Gente, desde o início deste blog (20/01/2006 - Não se esqueça da minha Caloi!) que este blogger anunciou: Disse adeus a Darwin e predizia uma ruptura iminente e eminente em biologia evolutiva.
Eu tentei de todas as maneiras que as informações que posto neste blog tivesse uma divulgação mais ampla na Grande Mídia, mas ela vive uma relação incestuosa despudorada com a Nomenklatura científica. Como soi bem a toda cortesã, nada fala sobre as dificuldades materiais, oops epistêmicas do amante. Sofre calada! Mas aqui neste blog, a gente mata a cobra e mostra o pau. Para desespero da Galera de meninos e meninas de Darwin - órfãos epistêmicos há muito tempo.
O pior de tudo é que o MEC/SEMTEC/PNLEM ainda aprova livros didáticos de Biologia do ensino médio com duas fraudes e várias distorções de evidências a favor do fato, Fato, FATO da evolução. Estamos de olho em 2010 em diante!
Gente, vem aí Darwin 3.0! Eu acho que o Bob Grant lê o meu blog!
Eu acho que vou sair e comemorar: a minha predição científica está sendo robustamente corroborada pelos darwinistas!
Darwin morreu, gente! Viva Darwin!!!
