Enhancing Evolution: When Spatial Structure and Environmental Change Improve Adaptation
Nahum, Joshua Richard
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Evolution by natural selection is the primary creative force in biology. In order for populations to thrive, or even survive, requires a continual generative process. An understand of the process of natural selection, its strengths and weaknesses, is necessary for both predictions about the future course of life, as well as its history. Evolution by natural selection requires the combination of three elements: variation, heredity, and selection. In natural populations, variation can be introduced by random mutation, recombination (such as by sex), and migration from differing populations. Heredity, or the correlation between traits of the parents with that of their offspring, is mediated by genetic material. Selection is the process whereby the traits of some members of the population are more successful (fit) and hence contribute more offspring to future generations. When these three factors are present, populations can (over the course of many generations) increase in fitness to become better adapted to their environment. The ability to adapt is not restricted to populations in natural environments, as artificial populations such as microbes grown in laboratory settings can also evolve. In fact, simulated, digital populations that possess the three features needed for evolution by natural selection can also adapt. In this dissertation, I utilize both microbes evolving in artificial settings and digital organisms, which exist only in a computer's memory, to make general statements about the process of evolution. Of course, such generalizations must be taken with a grain of salt, as the specifics of any system may interfere with assumptions made in the follow models. But, I present the following work as forays into the possible; I demonstrate that certain processes can affect the course of evolution, and such processes should be taken into account when seeking an understand of evolution in other (perhaps more natural) situations. In Chapter 1, I investigate how a non-transitive system of microbial competitors evolves, and demonstrate that the phenomenon of "survival of the weakest" requires the presence of population structure. In Chapter 2, I explore the effect of structure on evolving populations, and I find that structure can enhance the rate of adaptation in certain circumstances. Lastly in Chapter 3, I describe and demonstrate circumstances where environmental change can enhance the rate of adaption.
- Biology