The emergence of life depended on the ability of the first biopolymer populations to thrive and approach larger population sizes and longer sequences that could store enough information, as required for a cellular type of life. The evolution of these populations very likely occurred under circumstances under which Muller's Ratchet in synergism with random drift could have caused large genetic deterioration of the biopolymers. The genetic deterioration of the molecules caused by the accumulation

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... of mutations occurred during the copying process, can drive the populations to extinction unless there is a mechanism to counteract it. To test the effect of the mutation rate and the effective population size on the time to extinction, we used clonal populations of B16-19 ligase ribozymes, evolved with the continuous evolution in vitro system. The experiments were done using populations of 100, 300, 600 and/or 3000 molecules, and at low and high mutation rates. The errorprone Moloney Murine Leukemia virus reverse transcriptase was used with and without the addition of Mn(II). Populations evolved without Mn(II) were of four effective sizes. The times to extinction for those populations were found to be directly related to the effective size of the population. The small populations approached extinction at an average of 24.3 cycles; while the large populations did so at an average of 44.5 cycles. Genotypic characterization of the populations showed the presence of deleterious mutations in the small populations, which are the likely cause of their genetic deterioration and i Dr.