  A theoretical model is presented for early evolutionary cell sorting within
cellular aggregates. The model involves an energy-saving mechanism and
principles of collective self-organization analogous to those observed in
bicycle pelotons (groups of cyclists). The theoretical framework is applied to
slime-mold slugs (Dictyostelium discoideum) and incorporated into a computer
simulation which demonstrates principally the sorting of cells between the
anterior and posterior slug regions. The simulation relies on an existing
simulation of bicycle peloton dynamics which is modified to incorporate a
limited range of cell metabolic capacities among heterogeneous cells, along
with a tunable energy-expenditure parameter, referred to as an 'output-level'
or 'starvation-level' to reflect diminishing energetic supply, proto-cellular
dynamics are modelled for three output phases: 'active', 'suffering', and
'dying or dead.' Adjusting the starvation parameter causes cell differentiation
and sorting into sub-groups within the cellular aggregate. Tuning of the
starvation parameter demonstrates how weak or expired cells shuffle backward
within the cellular aggregate.
