Beyond Darwin: evolvability and the generation of novelty
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INTERVIEW
Open Access
Beyond Darwin: evolvability and the generation of novelty Marc Kirschner Marc Kirschner graduated in biochemistry from Northwestern University, moving to Berkeley for his doctoral research and with positions at Berkeley, Oxford University and Princeton before he took a professorship at University of California San Francisco where with Andrew Murray he did seminal research on the control of the cell cycle in Xenopus egg extracts that led to the discovery of how cyclin drives the cell cycle, and with Tim Mitchison on the dynamic instability of microtubules. In 1993 he moved to Harvard where in 2003 he became the founding Chair of the HMS Department of Systems Biology and was named the John Franklin Enders University Professor in 2009. The two books he wrote with John Gerhart, Cells, Embryos and Evolution (Blackwell, 1997) and The Plausibility of Life: Resolving Darwin’s Dilemma (Yale University Press, 2005), reflect his deep and longstanding interest in how biological systems evolve. Here he gives his view of the evolution of evolvability and its profound importance for understanding and applying biology.
What is evolvability - how would you define it? In some sort of tautological way evolvability is simply the capacity of a system to evolve. But more than that, in a Darwinian sense it speaks to both the amount of variation that is subject to selection, and the nature of that variation. And if there is something like evolvability, that would mean that systems are constructed in such a way that they generate a lot of phenotypic variation on which selection can act with a given amount, or a minimum amount, of genetic variation. But the variation must be variation of a special type: first of all, it has to be non-lethal because if it’s lethal it isn’t contributed to the next generation; and second, I would argue that it is a kind of variation that is more likely to be functional even for circumstances never previously encountered by the organism. That’s a little more difficult to explain, but Correspondence: [email protected] Department of Systems Biology, Harvard Medical School, Warren Alpert Building, 200 Longwood Avenue, Boston, MA 02115, USA
Marc Kirschner
effectively what I mean is that if you make random changes in mechanical systems they inevitably either have no effect or they break the system, whereas biological systems are able to survive random changes sometimes better, or often not so much worse; so biological systems are unusual in that you can make random changes and the system still functions, allowing random variation to accumulate. An important point here is that some of these features are used by the organism to adapt during its lifetime. There may be changes in the rate of cell division or the amount of a secreted molecule, or even the shape or mass of a bone, let’s say. But these are things that occur in the normal physiology of the organism, which is clearly under selection, so the system has evolved to accommodate them. Once you replace that physiological selection wit
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