Biology and Philosophy

, Volume 20, Issue 5, pp 967–987 | Cite as

On the transfer of fitness from the cell to the multicellular organism

  • Richard E. MichodEmail author


The fitness of any evolutionary unit can be understood in terms of its two basic components: fecundity (reproduction) and viability (survival). Trade-offs between these fitness components drive the evolution of life-history traits in extant multicellular organisms. We argue that these trade-offs gain special significance during the transition from unicellular to multicellular life. In particular, the evolution of germ–soma specialization and the emergence of individuality at the cell group (or organism) level are also consequences of trade-offs between the two basic fitness components, or so we argue using a multilevel selection approach. During the origin of multicellularity, we study how the group trade-offs between viability and fecundity are initially determined by the cell level trade-offs, but as the transition proceeds, the fitness trade-offs at the group level depart from those at the cell level. We predict that these trade-offs begin with concave curvature in single-celled organisms but become increasingly convex as group size increases in multicellular organisms. We argue that the increasingly convex curvature of the trade-off function is driven by the cost of reproduction which increases as group size increases. We consider aspects of the biology of the volvocine green algae – which contain both unicellular and multicellular members – to illustrate the principles and conclusions discussed.

Key words

Body size Cost of reproduction Evolutionary transitions Fitness Germ–soma specialization Individuality Life-history evolution Multi-level selection Multicellularity Volvox 


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Research supported by NSF grant DEB-9527716. The ideas presented here have been discussed and developed with the help of many colleagues, especially, in alphabetical order, M. Herron, M. Hurrand, T. Huxman, J. Kessler, A. Nedelcu, D. Roze, C. Solari, and Y. Viossat. I also appreciate the comments of S. Okasha which improved the manuscript.


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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  1. 1.Department of Ecology and Evolutionary BiologyUniversity of ArizonaTucsonUSA

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