Abstract

If the coming of the last universal cellular ancestor marks the crossing of the “Darwinian Threshold”, pre-LUCA evolution must have been pre-Darwinian. But how did pre-Darwinian evolution actually operate? Bringing together and extending insights from both earlier and more recent contributions, this essay advances three principal arguments regarding the pre-Darwinian evolution. First, in the pre-Darwinian epoch, survival essentially meant persistence within the prebiotic system, and it depended mostly on chemical variation and interaction. Second, selection operated upon four different properties: chemical; chemical-physical; vesicles’ capacities in absorbing, engulfing, and merging; and protocells’ coupling of metabolism, replication, and division. Third, division evolved from a state without tight coupling of replication with division to a state of tight coupling. Eventually, protocells with a tight coupling of replication with division became the First Universal Cellular Ancestors and then LUCA.