  How multicellular life forms evolved out from unicellular ones constitutes a
major problem in our understanding of the evolution of our biosphere. A recent
set of experiments involving yeast cell populations has shown that selection
for faster sedimenting cells leads to the appearance of stable aggregates of
cells that are able to split into smaller clusters. It was suggested that the
observed evolutionary patterns could be the result of evolved programs
affecting cell death. Here we show, using a simple model of cell-cell
interactions and evolving adhesion rates, that the observed patterns in cluster
size and localized mortality can be easily interpreted in terms of waste
accumulation and toxicity driven apoptosis. This simple mechanism would have
played a key role in the early evolution of multicellular life forms based on
both aggregative and clonal development. The potential extensions of this work
and its implications for natural and synthetic multicellularity are discussed.
