Is it time to rework evolutionary biology’s “modern synthesis”?

July 29, 2008 | By | 2 Replies More

The July 11, 2008 edition of Science (available only to subscribers on line) includes an article entitled “Modernizing the Modern Synthesis,” by Elizabeth Pennisi, regarding a group of scientists who call themselves “The Altenberg 16.” They have gathered together to explore the need to revamp the modern synthesis. What is the “modern synthesis”? According to Wikipedia, the modern synthesis “bridged the gap between experimental geneticists and naturalists; and between both and palaeontologists, stating that”:

  • All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms and the observational evidence of naturalists.
  • Evolution is gradual: small genetic changes, recombination ordered by natural selection. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction (not saltation).
  • Selection is overwhelmingly the main mechanism of change; even slight advantages are important when continued. The object of selection is the phenotype in its surrounding environment. The role of genetic drift is equivocal; though strongly supported initially by Dobzhansky, it was downgraded later as results from ecological genetics were obtained.
  • The primacy of population thinking: the genetic diversity carried in natural populations is a key factor in evolution. The strength of natural selection in the wild was greater than expected; the effect of ecological factors such as niche occupation and the significance of barriers to gene flow are all important.
  • In palaeontology, the ability to explain historical observations by extrapolation from micro to macro-evolution is proposed. Historical contingency means explanations at different levels may exist. Gradualism does not mean constant rate of change.

According to “Modernizing the Modern Synthesis,” the modern synthesis thus holds that:

Organisms have a repertoire of traits that are passed down through the generations. Vacations in genes alter those traits bit by bit and if conditions are such that those alterations make an individual more fit, and the altered trade becomes more common over time. This process is called natural selection. In some cases, the new feature can replace an old one; in other instances, natural selection also leads to speciation.

The modern synthesis has guided biologists for the past 70 years. The obvious question, then is what has happened since then to necessitate any changes to the modern synthesis?

A lot has happened in the past half-century. DNA’s structure was revealed, genomes were sequenced, and developmental biologist turned their sights on evolutionary questions. Researchers have come to realize that heredity is not simply a matter of passing genes from parent to offspring, as the environment, chemical modification of DNA, and other factors come into play as well. Organisms vary not only in how they adapt to changing conditions but also in how they evolve.

One of the organizers of the group, evolutionary biologist Massimo Pigliucci stresses that the need for a reworking of the modern synthesis doesn’t mean that the overall theory of evolution is wrong (as “intelligent design” advocates will no doubt argue). Rather, the group is attempting to “better incorporate modern science and the data revealed by it.”

The Pennisi article serves as a succinct review of some of the new research that needs to be incorporated into evolutionary biology. Many of these developments “are nudging evolutionary biology away from a focus on population genetics-how the distribution of genes changes across groups of individuals-and toward an understanding of the molecular underpinnings of these changes.”

One of the basic ideas that needs to be incorporated is that DNA cannot do it all–biology is highly constrained by physics and this needs to be recognized. Evolutionary biologist Gunter Wagner explains that under the “old” modern synthesis, “the body plan is a historical residue of evolutionary time, the afterglow of the evolutionary process such that more closely related organisms share more features.” The “new” view is that body plans have internal inertia and evolution works around this stability.”

Other new developments include the recognition of the importance of “regulation,” which is largely ignored by the modern synthesis. Under the new approach, changing the regulation of only if you factors “could help coordinate the systemic changes needed to make a new trait, helping to ensure that larger muscles co-evolve with bigger jawbones for more powerful bite.”

The standard modern synthesis also fails to take into account “epigenetics.” A small chemical modification of DNA can have dramatic effects and can actually travel through generations of offspring. The author gives another example of chemical modifications that influence how tightly wound DNA is. This coiling can actually “alter the rate of mutation, the ease by which mobile elements can move around, the duplication of genes, and even how much gene exchange occurs between matching chromosomes.

The Altenberg 16 group is also exploring the role of “evolvability,” which considers “the inherent capacity of an organism or population, even a species, to respond to a changing environment.” This is a concept introduced to explain why certain types of organisms are more prone to greater diversification.

As the above-cited article indicates, some of these ideas have their skeptics, though the Altenberg 16 group sees it to be an important task to bring these ideas together for further coordinated exploration.

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Category: Evolution, Science

About the Author ()

Erich Vieth is an attorney focusing on consumer law litigation and appellate practice. He is also a working musician and a writer, having founded Dangerous Intersection in 2006. Erich lives in the Shaw Neighborhood of St. Louis, Missouri, where he lives half-time with his two extraordinary daughters.

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  1. Flora Korkis says:

    This Altenberg group… this is the group that wants to recreate the creation of the world in a small model, right? If so, I'm very excited about it. Also, I heavily enjoyed reading this. Keep up the good work.

  2. Erich Vieth says:

    Lots more "evo-devo" (the synthesis between evolution and development) and on the Pigliucci's Altenberg group in the 9/18/08 edition of Nature. Here's an excerpt:

    "You can't deny the force of selection in genetic evolution," says [Stuart] Newman, "but in my view this is stabilizing and fine-tuning forms that originate due to other processes." The same process might have given rise to animals themselves. The further you turn back the clock through geological time, Newman believes, the weaker genetic regulation of development becomes relative to plasticity and self-organization. The development of the most basic feature s of multi-cellular organisms some 600 million years ago, in the late Proterozoic, might have been the rapid and spontaneous result of molecules already present on unicellular organism doing new jobs when cells stick together. "You don't need incremental change under gradual selection regimes to get attributes such as segmented, hollow or multi-layered bodies," says Newman. "You can get it all with thermodynamics and self-organization." The problem is testing such ideas . . .

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