Selection and the Origin of Cells

Cells are the smallest known pieces of biology that are capable of independent reproduction and are therefore the simplest units that can evolve by conventional natural selection. This is problematic because even the simplest self-replicating cell-like entities seem to be too complicated to arise without the guiding hand of selection. To solve this conundrum, I argue that selection began before there were bounded entities in the form of neighborhood selection, an analog of group selection without bounded groups. This, I suggest, acted on chemical consortia bound to mineral surfaces to enhance their autocatalytic abilities. Then, selection for an ability to colonize new mineral surfaces resulted in the origin of propagules, which later evolved into free-living protocells. This model implies that much of life’s complexity is the product of selection rather than of chance and that cells might arise predictably and rapidly in any environment with abundant free energy and appropriate chemical building blocks.