Fig. 4

A brief outline of steps from prokaryotic cells in a matrix to a progenitor eukaryotic cell. a A transient consortium of prokaryotic cells (red Archaea, blue bacteria) in a biofilm-like or matrix undergoes a transformation to a stable ensemble of cells that encourages gene transfer resulting in increasingly hybridized genomes. Physical merger of cells results in multigenomes, with division of labour resulting in differentiation into mitochondria and nucleus. b In the yellow stream, a primitive nucleus emerges from a population of prokaryotic cells in a stable matrix through a succession of gene transfers resulting in merged genomes followed by cell fusions to result in multi-genome structures with multiple non-identical chromosomes. The genetic redundancy of the process supports the evolution of complex molecular pathways. b In the blue stream, developing interdependence among cells in a stable matrix allows for the emergence of increasingly elaborate protein networks that are supported by matrix-based (and ultimately cytoplasmic) ribosomes. In the green stream, as the population becomes progressively interdependent some cells in the matrix become ATP secretors, supplementing the energy needs of other cells and ultimately evolving into primitive mitochondria. Please consult the main text for more information