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Evolvability

This seminar explores the concept of evolvability in biological systems, discussing its definitions and scales. It investigates the relationship between evolvability and robustness, as well as the role of modularity in genetic variation. The seminar also delves into the evolution of evolvability and its significance at different levels of evolution.

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Evolvability

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  1. Stephan Hoyer Physics 120 seminar March 28, 2008 Evolvability

  2. What is evolvability? • Two definitions: • A biological system is evolvable if its properties show heritable genetic variation, and if natural selection can thus change these properties • A biological system is evolvable if its properties can acquire novel functions through genetic change, functions that help the organism survive and reproduce

  3. “Evolvability” at different scales Massimo Pigliucci. Is evolvability evolvable? Nature Reviews Genetics 9, 75-82 (January 2008)

  4. Extra eyes on Drosophila Modular Robust? Halder, G., P. Callerts, and W. J. Gehring. Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila. Science267, 1788-1792 (1995).

  5. Robustness • A biological system is robust if it continues to function in the face of perturbations • For living things: • Genetic robustness • Environmental robustness • Different levels: • Changes in genotype not reflected in phenotype • Overall fitness… to survive, reproduce, etc

  6. Does robustness help evolvability? • Robustness hurts: • Less phenotypic variation => Less selective pressure => less evolvability. • Robustness helps: • Versatility: for other non-robust traits • Neutrality: robustness means more silent mutations to set stage for important ones. • As Capacitors: when robustness breaks, hidden variation is released

  7. Evolvability in fitness landscapes Q: What’s wrong with this picture? A: Far too few dimensions!

  8. Neutral spaces • Visualizing fitness landscapes gives you way too few dimensions! • Peak shift problem: how do you move between peaks? • High dimensional (100-1000D) landscapes are qualitatively different • Neutral spaces allow for lots of variation • Techniques from physics: percolation theory and simulation Gavirlets, S. A dynamical theory of speciation on holey adaptive landscapes. Am. Nat.154, 1-22 (1999).

  9. Why robustness? • Clearly life actually is very robust • Easier to get to by chance most stuff exists in the large neutral space • Natural selection can select for robustness in neutral spaces

  10. Modularity • Modularity helps evolvability? • Are modular systems robust? • Altering one module is less likely to disrupt others • But that one module can still disrupt everything if it’s essential • Also requires redundancy, most not in genes, but in alternate methods

  11. How does evolvability evolve? • Clearly there are big steps in evolvability, e.g. • Multi-cellularity • Animals • Appendages • etc • Is evolvability a side-result or the end-goal of evolution? • Brings up issue of evolution at different levels: for individuals or for species?

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