Richard Michod (University of Arizona, USA) (Virtual)Reorganization of fitness during evolutionary transitions in individuality *PhilInBioMed Seminar, organized by Thomas Pradeu* *January 28th, 2026, 5pm French time (UTC+1)* Richard Michod is Professor of Ecology and Evolutionary Biology, at the University of Arizona, USA. He is a world-leading expert on evolutionary biology, evolutionary transitions, and multicellularity. His favorite experimental model is the volvocine green algae. Rick is an excellent biologist with deep conceptual and philosophical thinking, as illustrated by his book Darwinian Dynamics: evolutionary transitions in fitness and individuality and by his many papers published in major journals in biology and philosophy of biology. *Zoom link:* https://u-bordeaux-fr.zoom.us/j/81626413626?pwd=rakvxrTrTmCjPZVuQYl4xgbVp4YSeg.1 *Detailed information:* https://philinbiomed.cnrs.fr/event/richard-michod-reorganization-fitness/ *Abstract* The central question of this talk is: *How do groups of individuals become new kinds of individuals?* I approach evolutionary transitions in individuality (ETIs) as dynamic multilevel selection (MLS) processes in which cooperation, conflict, and conflict mediation reorganize fitness from lower to higher levels. Using mathematical models and the volvocine green algae as a model system, I show how cooperation arises from ancestral survival–reproduction trade‑offs, and that cooperation inevitably generates conflict through mutations that increase cell-level replication at the expense of the group. The key evolutionary and developmental innovations are *conflict modifiers*—germ‑line sequestration, policing, programmed cell death, mutation‑rate reduction, and determinate size control. These modifiers do more than stabilize cooperation: they *alter the structure of selection*, suppressing within‑group selection while amplifying between‑group covariance in fitness, thereby permitting complex adaptations to emerge at the new level. Two‑locus modifier models and Price‑equation partitions reveal how conflict mediators reduce within‑group change and increase group‑level heritable variance in fitness. When between‑group covariance dominates, selection favors alleles that enhance group-level heritability, enabling *fitness transfer* and *fitness decoupling* between cells and the collective. At this point, the stabilized group becomes a *new focus level of complex adaptation*, capable of coordinated development, group level reproduction, and life cycles integrated at the group level. ETIs thus build new evolutionary individuals, opening new adaptive possibilities not accessible at the lower level. Multicellular individuality emerges as the cumulative outcome of MLS dynamics, not as a predefined endpoint. *Positions and Education* - Professor, Ecology and Evolutionary Biology, University of Arizona, 1987 – present. - Associate Professor, Ecology and Evolutionary Biology, University of Arizona, 1982 – 1987. - Assistant Professor, Ecology and Evolutionary Biology, University of Arizona, 1978-1982. - Ph.D., Genetics, Zoology, University of Georgia, 1978 - M.A., Mathematics, University of Georgia, 1978. - B.S., Zoology, Duke University, 1973 *Research Interests* The Michod Lab is studying the evolution of multicellularity and sex in the volvocine green algae as examples of evolutionary transitions in individuality. How groups of individuals become new kinds of individuals is the basic question that motivates us. Understanding evolutionary transitions in individuality is key to understanding one of the most familiar features of the living world, its hierarchical organization. We use methods from theoretical population biology, molecular biology, genomics, ecology, and philosophy. *Selected Publications* 1. Solari, C.A., J. O. Kessler, and R. E. Michod. 2006. A hydrodynamics approach to the evolution of multicellularity: Flagellar motility and cell differentiation in volvocalean green algae. *American Naturalist*. 167:537-554. (PDF ). Receipient of the President’s Award Paper of the Year in American Naturalist for 2006. 2. Solari, C. A., S. Ganguly, J. O. Kessler, R. E. Michod, and R. E. Goldstein. 2006. Multicellularity and the functional interdependence of motility and molecular transport. *Proceedings of the National Academy of Sciences*, USA. 103:1353-1358. (PDF ) 3. Michod, R.E. 2006. The group covariance effect and fitness trade-offs during evolutionary transitions. *PNAS*, USA. 103:9113-9117.(PDF ) 4. Nedelcu A.M., Michod R.E. 2006. The evolutionary origin of an altruistic gene in *Volvox carteri*. *Molecular Biology and Evolution*. 8:1460-1464. (PDF ) 5. Michod R.E., Herron M.D. 2006. Cooperation and conflict during evolutionary transitions in individuality. *Journal of Evolutionary Biology*.19:1406-1409. (PDF ) 6. Michod, R.E. 2007. Evolution of individuality during the transition from unicellular to multicellular life. *PNAS*, USA. 104: 8613-8618. (PDF ) 7. Michod, R.E. 2007. Evolution of individuality during the transition from unicellular to multicellular life. In: I*n the light of evolution: Volume 1. Adaptation and complex design*, edited by J. C. Avise and F. J. Ayala, Washington, D.C.:The National Academies Press, p. 129-144. 8. Michod, R.E. H. Bernstein, and A. M. Nedelcu. 2008. Adaptive value of sex in microbial pathogens. *Infection, Genetics and Evolution* 8:267–285. (PDF ) 9. Herron, M.D. and R. E. Michod. 2008. Evolution of complexity in the volvocine algae: transitions in individuality through Darwin’s eye. *Evolution*. 62-2: 436–451. (PDF ) 10. Soari, C. A., Michod, R. E. and R. E. Goldstein. 2008. *Volvox barberi*, the fastest swimmer of the volvocales (chlorophyceae). *J. Phycol*. 44, 1395–1398. (PDF ) 11. Michod R.E. 2009. Social evolution and sex: Cooperation and conflict from molecules to societies. In *Aux origines du sexe*. Edited by A. Civard-Racinais and P. H. Gouyon. Paris:Fayard. In press. 12. Michod, R.E. 2009. Sex and multicellularity as evolutionary transitions in individuality. In: *Major Transitions in Evolution Revisited*, edited by K. Sterelny and B. Calcott, Altenberg, Austria:Konrad Lorenz Institute. 13. Shelton,D.E. and R.E. Michod. 2009. Philosophical foundations for the hierarchy of life (Book review of Evolution and the Levels of Selection by Samir Okasha). *Biology and Philosophy, *In press*.* 14. Herron, M.D., J.D. Hackett, F.O. Aylward and R.E. Michod. 2009. Triassic origin and early radiation of multicellular volvocine algae. *PNAS*, USA. Early Edition. (PDF ) 15. Michod, R.E. 2009. Sex and multicellularity as evolutionary transitions in individuality. In: Major Transitions in Evolution Revisited, edited by K. Sterelny and B. Calcott, Altenberg, Austria:Konrad Lorenz Institute. 16. Michod R.E. 2009. Socialite et sexe : Coopération et conflit : des molécules aux sociétés. In Aux origines du sexe. Edited by A. Civard-Racinais and P. H. Gouyon. Paris:Fayard. In press. 17. Shelton, D. E. and R. E. Michod. (In press). Philosophical foundations for the hierarchy of life (Book review of *Evolution and the Levels of Selection *by Samir Okasha). *Biology and Philosophy*. 18. Solari C.A., Ganguly S., Kessler J.O., Michod R.E., and Goldstein R.E. Phenotypic plasticity of flagellar motility in *Volvox* due to changes in nutrient concentration. (submitted). 19. Proceedings of the Royal Society B, submitted. Herron, M. D., A. G. Desnitskiy, and R. E. Michod. (submitted). Evolution of developmental programs in* Volvox* (Chlorophyta).*J. Phycol*. 20. Michod, R.E. 2010. Sociality and sex: Cooperation and conflict from molecules to societies. In. Michod, R.E. and M.D. Herron (eds). CoS Evolution lectures. 21. Michod, R.E. and M.D. Herron. 2010. (eds) CoS Evolution lectures. Sincerely, Thomas. -- Thomas Pradeu CNRS Research Director in Philosophy of Science Immunology Unit ImmunoConcEpT, UMR5164, CNRS & University of Bordeaux Presidential Fellow, Chapman University, CA, USA Team Leader Conceptual Biology and Medicine Team Coordinator of the Philosophy in Biology and Medicine Network (PhilInBioMed) & Institute for the History and Philosophy of Science and Technology Pantheon-Sorbonne University 13 rue du Four, 75006 Paris, France *Recent publications: * - Immunological surveillance against cancer across mammals (*Nat Commun*, 2025) - Advancing cancer research via comparative oncology (*Nature Reviews Cancer*, 2025) - Is “pre-sepsis” the new sepsis? A narrative review (*PLoS Pathog*, 2025) - Philosophy in Science: Can philosophers of science permeate through science and produce scientific knowledge? ( *BJPS*, 2024). - The conceptual foundations of innate immunity: Taking stock 30 years later (*Immunity*, 2024) Thomas Pradeu (to subscribe/unsubscribe the EvolDir send mail to golding@mcmaster.ca)