Pigliucci on Expanding the Synthesis
Nature recently ran this interesting book review by Massimo Pigliucci. The book under review is Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life by Eva Jablonka and Marion J. Lamb. Pigliucci writes:
There have been rumblings for some time to the effect that the neo-darwinian synthesis of the early twentieth century is incomplete and due for a major revision. In the past decade, several authors have written books to articulate this feeling and to begin the move towards a second synthesis. David Rollo, in his book Phenotypes (Kluwer, 1994), was among the first to attempt to bring the focus back to the problems posed by phenotypic evolution. In Phenotypic Evolution (Sinauer, 1998), Carl Schlichting and I framed the debate in terms of the integration of development, environment and genetics by articulating the concept of “developmental reaction norms”. Stephen Jay Gould then produced an overly long (and at times acrimonious) sketch of the new synthesis in The Structure of Evolutionary Theory (Harvard University Press, 2002). Finally, Mary-Jane West-Eberhard, in Developmental Plasticity and Evolution (Oxford University Press, 2003), greatly expanded on my book and the one by Rollo, producing the most comprehensive alternative account of evolutionary theory yet. Evolution in Four Dimensions by Eva Jablonka and Marion Lamb is the most recent addition to this genre, and contributes yet another valuable perspective to the discussion.
Jablonka and Lamb, as described by Pigliucci, argue that there are really four different sources of inheritance. He writes:
The authors argue that there is more to heredity than genes; that some hereditary variations are non-random in origin; that some acquired information is inherited; and that evolutionary change can result from 'instruction' as well as selection. This may sound rather revolutionary, even preposterously close to lamarckism. But Jablonka and Lamb build on evidence from standard research in evolutionary and molecular biology, and their case should be examined on its merits, rather than being dismissed by a knee-jerk reaction.
Consider the charge of lamarckism. Jablonka and Lamb happily embrace the term, but with one important qualification. As they correctly point out, there are at least two very distinct meanings of the word. Most biologists associate lamarckism with the idea of direct adaptive feedback from the soma to the germ line. That version of lamarckism is dead, killed off by our understanding of molecular biology, and nobody is attempting to revive it.
The second meaning is actually closer to the core of Lamarck's ideas, which are rarely, if ever, read by modern biologists. The suggestion is that some heritable, adaptive changes come not from natural selection, but from the action of evolved internal systems that generate non-random 'guesses' in response to environmental challenges. Examples are not hard to find, contrary to the assumed wisdom of standard neo-darwinism. Consider the existence of 'hotspots' that make mutations in certain regions of the genome much more likely than in others. Or the impressive ability of some bacteria to increase the mutation rate of a specific gene involved in the metabolism of a given amino acid when that amino acid becomes scarce in the environment.
The whole review is worth reading. And the book itself has now been added to the queue.
I have commented before at this blog that the problem facing evolutionary biologists is never “How could bit of anatomy X possibly have evolved naturally?” Rather, the question is “Of the many possible mechanisms by which this system might have evolved, which is the correct one?” It seems that scientists are constantly discovering new mechanisms for explaining evolution, even to the point of unseating natural selection as the sole crafter of adaptive change (if Jablonka and Lamb are correct). This is enormously exciting stuff.
Of course, any talk of fiddling with the neo-Darwinian synthesis tends to make the hearts of creationists go pitter pat. They know that any suggestion that the nineteen fifties version of evolution may have been incomplete can be spun into a statement that evolution is dying. They will conveniently ignore the fact that the discoveries that are pursuading scientists of the incompleteness of the original synthesis are all in the direction of making evolutionary change easier, not harder, to explain. They won't mention that evolutionary theory is strengthened by the developments Pigliucci describes.
The crafters of the original synthesis restricted their explanatory options unnecessarily. The reality is that biologists are faced with an embarrassment of riches in trying to explain evolutionary change.