  The rise of multicellularity in the early evolution of life represents a
major challenge for evolutionary biology. Guidance for finding answers has
emerged from disparate fields, from phylogenetics to modelling and synthetic
biology, but little is known about the potential origins of multicellular
aggregates before genetic programs took full control of developmental
processes. Such aggregates should involve spatial organisation of
differentiated cells and the modification of flows and concentrations of
metabolites within well defined boundaries. Here we show that, in an
environment where limited nutrients and toxic metabolites are introduced, a
population of cells capable of stochastic differentiation and differential
adhesion can develop into multicellular aggregates with a complex internal
structure. The morphospace of possible patterns is shown to be very rich,
including proto-organisms that display a high degree of organisational
complexity, far beyond simple heterogeneous populations of cells. Our findings
reveal that there is a potentially enormous richness of organismal complexity
between simple mixed cooperators and embodied living organisms.
