Abstract
If the coming of the last universal cellular ancestor (LUCA) marks the crossing of the “Darwinian Threshold” (Woese in Proc Natl Acad Sci USA 99:8742–8747, 2002), 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 (FUCAs) and then LUCA.
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