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Abstract:
The evolution of multicellular organisms from unicellular counterparts involved a transition in
Darwinian individuality from single cells to groups. A particular challenge is to understand the
nature of the earliest groups, the causes of their evolution, and the opportunities for emergence
of Darwinian properties. Here we outline a conceptual framework based on a logical set of
possible pathways for evolution of the simplest self-replicating groups. Central to these
pathways is the recognition of a finite number of routes by which genetic information can be
transmitted between individual cells and groups. We describe the form and organization of
each primordial group state and consider factors affecting persistence and evolution of the
nascent multicellular forms. Implications arising from our conceptual framework become
apparent when attempting to partition fitness effects at individual and group levels. These are
discussed with reference to the evolutionary emergence of individuality and its manifestation
in extant multicellular life—including those of marginal Darwinian status.
