The first major transition: Origin of life from a multilevel selection perspective

Abstract

The origin of life is the first, arguably, the most important and also the most enigmatic major transition in evolution (MTE). As all MTE, the transition at the origin of life can be constructively addressed only within the conceptual framework of multilevel selection. The two levels of selection relevant for the origin of life are replicators, and reproducers, that is, compartments (protocells) capable of reproduction via a primitive form of division. The symbiotic model for the origin of life presented here posits that cellular life was preceded by protocells that harbored proto-metabolic networks but not genetic elements (replicators), Replicators could have started as selfish elements inside protocells selected only for replication efficiency, but subsequently, would evolve into mutualists such that the reproducer-replicator union became a new, collective unit of selection. Mathematical modeling of replicator-reproducer coevolution identifies the conditions under which replicator-carrying protocells can outcompete empty protocells. For the replicator-carrying protocells to and get fixed in evolution, replication has to be coupled with protocell division, selection for the highest replication rate being partially suppressed. At the earliest stages of evolution, random, stochastic protocell division was advantageous compared to symmetrical division. The multilevel selection perspective illuminates the likely order of key events on the evolutionary route from ensembles of chemicals to cells endowed with genomes, symmetrical cell division and anti-parasite defense systems.