Evolutionary transitions in individuality
Evolutionary transitions in individuality are events in which groups of previously independent replicators become new evolutionary individuals: genes into chromosomes, prokaryotic cells into eukaryotic cells, single cells into multicellular organisms, solitary organisms into societies.
The framework
John Maynard Smith and Eörs Szathmáry organized the history of life around this sequence in The Major Transitions in Evolution (1995). Each transition changes how hereditary information is stored and transmitted, and each raises the same two questions: why do the parts cooperate, and what stops a part from defecting?
What a transition requires
Leo Buss argued in The Evolution of Individuality (1987) that the obstacle is conflict among cell lineages, and that developmental mechanisms — a single-cell bottleneck, germline sequestration — evolved to suppress it. Richard Michod formulated the same process in fitness terms: during a transition, fitness exports from the lower-level units to the collective, and the collective mediates conflict among its parts. Godfrey-Smith’s de-Darwinization framework describes the same requirements in philosophical vocabulary: the parts must lose variation, heritability, and differential fitness of their own.
The transitions framework is the standard context for treating cancer as a failure of individuality — a reversion of cells to independent Darwinian behavior within a body that evolved to suppress it.
Notes
- Draft stub — maintenance agent to expand with the full transition list, the bottleneck/germline argument in detail, and the volvocine algae evidence.