Evolution of individuality during the transition from unicellular to multicellular life
Open accessAbstract
Individuality is a complex trait, yet a series of stages each advantageous in itself can be shown to exist allowing evolution to get from unicellular individuals to multicellular individuals. We consider several of the key stages involved in this transition: the initial advantage of group formation, the origin of reproductive altruism within the group, and the further specialization of cell types as groups increase in size. How do groups become individuals? This is the central question we address. Our hypothesis is that fitness tradeoffs drive the transition of a cell group into a multicellular individual through the evolution of cells specialized at reproductive and vegetative functions of the group. We have modeled this hypothesis and have tested our models in two ways. We have studied the origin of the genetic basis for reproductive altruism (somatic cells specialized at vegetative functions) in the multicellular Volvox carteri by showing how an altruistic gene may have originated through cooption of a life-history tradeoff gene present in a unicellular ancestor. Second, we ask why reproductive altruism and individuality arise only in the larger members of the volvocine group (recognizing that high levels of kinship are present in all volvocine algae groups). Our answer is that the selective pressures leading to reproductive altruism stem from the increasing cost of reproduction with increasing group size. Concepts from population genetics and evolutionary biology appear to be sufficient to explain complexity, at least as it relates to the problem of the major transitions between the different kinds of evolutionary individuals.
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- Authors
- Michod, R. E.
- Affiliations
- University of Arizona (US)
- Corresponding author
- Michod, Richard E.
- ORCID
- Michod, Richard E.
- Venue
- Proceedings of the National Academy of Sciences
- Publisher
- National Academy of Sciences
- Published
- 2007-05-15
- Volume
- 104
- Issue
- suppl_1
- Pages
- 8613-8618
- ISSN
- 0027-8424 (ISSN-L)
- 1091-6490
- PMC
- PMC1876437
- OpenAlex
- W2104287464
- Cited by
- 334
- References
- 42
- Citations by year
- 2026: 17 · 2025: 36 · 2024: 13 · 2023: 15 · 2022: 13 · 2021: 24 · 2020: 17 · 2019: 21 · 2018: 18 · 2017: 22 · 2016: 16 · 2015: 17 · 2014: 13 · 2013: 18 · 2012: 11
- FWCI
- 9.28
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Proceedings of the National Academy of Sciences (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Evolution and Genetic Dynamics
- Social Sciences › Sociology and Political Science › Evolutionary Game Theory and Cooperation
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protist diversity and phylogeny
- Keywords
- multicellularity, individuality, reproductive altruism, fitness trade-offs, Volvox carteri, volvocine algae, kin selection, group size, life-history trade-offs, evolution of complexity
- MeSH terms
- Biological Evolution, Volvox
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