Primordial sex facilitates the emergence of evolvable protocells Sam Sinai ' ' , Jason Olejarz , lulia A. Neagu , and Martin A. Nowale.b." "Program for Evolutionary Dynamics. HarvaM University. I Brame square. suite 6.02138; hDepanment of Organismic and Evolutionary Biology; `Department of Mathematics; dOepariment of Physics. Harvard University This manuscript was compiled on April x.2016 Membranes, forming protocells, are widely considered beneficial or even essential to the maintenance of cooperation in early evolution [1-5). Moreover, there are strong arguments from chemistry to sug- gest that membranes played a critical role in pre-evolutionary dynam- ics [6-9). In this study we propose a novel reason why membranes are beneficial even before the presence of replication or selection. We argue that the ability of lipid membranes to fuse and share their contents. "primordial sex", improves the efficiency of finding mini- mal evolvable protocells. We analyze and quantify a model of merg- ing membranes that resembles a sexual repair mechanism known as multiplicity reactivation in modern viruses [10). We then argue that this mechanism could shorten the timescale and increase the probability of finding evolvable combinations of simple functional elements significantly. This in turn suggests that assembling com- plicated sets of functions at random may not be as probabilistically implausible as it first appears. Hence, in the presence of sex, large assemblies and functional networks can form without requiring evo- lution. Finally, we establish a quantitative framework to analyze how parasites, thought to be a serious impediment in early life. affect the accumulation of functions. We show that while parasites may hurt the accumulation process, under most circumstances, the ben- efits of sex massively outweigh the risks of exposure to parasitic elements. Origin of Life I Protocells I Origin of Sex I Multiplicity Reactivation M enthrones are ubiqui