Deem, Michael W2019-05-162019-05-162017-082017-08-04August 201Wang, Dong. "Effect of Modularity on Evolution in Heterogeneous Environments." (2017) Diss., Rice University. <a href="https://hdl.handle.net/1911/105471">https://hdl.handle.net/1911/105471</a>.https://hdl.handle.net/1911/105471Biological systems are modular. It is natural to ask the question: why are biological systems modular? We show that under certain circumstances, being modular is beneficial. For example, when the environment changes, modularity coupled with horizontal gene transfer accelerates the adaptation of individuals. We have proved this result theoretically using a spin glass model of fitness, and we quantify the evolutionary advantage analytically. To establish the generality of this result, we apply other models of the fitness, such as Potts model or generalized NK model, to this problem, finding similar results. Simulations generate results consistent with our analytical calculations. Biological populations migrate at all scales. When individuals in a population migrate, they experience changing environments. What role does modularity play in the migration process? Under what conditions is modularity helpful? We generalize our model in one environment to several correlated environments with migrating individuals. We apply this model to two real world scenarios. First we study the migration of ancient humans in the Americas, and quantify how migration velocity depends on environmental gradient. In addition, we show that a modular knowledge system and frequent knowledge transfer accelerate the migration velocity. Second, we study bacteria in heterogeneous environments, showing that their resistance to antibiotics emerges very quickly in an antibiotic gradient. We show that a modular organization of genes accelerates this emergence of resistance, and we quantify how mutation rate, horizontal gene transfer rate, nutrients, and antibiotic gradient influence this emergence.application/pdfengCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.ModularityEvolutionThesis2019-05-16