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Dr. Michael Muthukrishna,University of British Columbia

The Cultural Brain Hypothesis and the Transmission and Evolution of Culture

Humans are an undeniably remarkable species with massive brains, amazing technology, and large, well-connected social networks. The co-occurrence of these traits is no accident. My dissertation introduced the Cultural Brain Hypothesis and Cumulative Cultural Brain Hypothesis. The Cultural Brain Hypothesis is a single theory that explains the increase in brain size across many taxonomic groups. In doing so, the theory makes predictions about the relationships between brain size, knowledge, group size, social learning, and the length of the juvenile period. These predictions are consistent with existing empirical literature, tying together relationships that presently have separate explanations. The Cumulative Cultural Brain Hypothesis makes predictions about the conditions under which these evolutionary processes lead to a positive feedback loop between brain size and knowledge, ratchetting both upward in a co-evolutionary duet. I argue that these conditions, such as (counter-intuitively) a tendency to learn without understanding, are the key to the uniquely human pathway, explaining our large brains and various aspects of our psychology. I tested many of these theories across 4 experiments with human subjects. These experiments offered support for a causal relationship between population size and interconnectedness, and technological complexity, and revealed the environmental and individual predictors of biased social learning. In the final chapter, I laid the groundwork for improving the way in which these theories account for human societies by proposing an extension to explain uniquely human social structures. I concluded by discussing how this approach to studying humans could help move us toward a general Theory of Human Behavior in a way that both connects psychology to the biological sciences and integrates it with the rest of the social sciences.


Dr. Scott Cushing, West Virginia University

Plasmonic Enhancement Mechanisms in Solar Energy Harvesting

Efficient solar energy conversion is a balance of absorbing the most sunlight in the thinnest semiconductor possible. A promising solution to this problem is shrinking gold and silver to a billionth of a meter to form nanoparticles. Under these conditions, a plasmon resonance is formed, with the metal’s entire conduction electron density oscillating in harmony with the frequency of sunlight. This allows the metal nanoparticle to concentrate sunlight like an antenna that is thousands of times its physical size. Plasmonics promises to increase solar energy conversion efficiencies by letting the semiconductor absorb the same amount of sunlight while being a thousand times thinner. This thesis investigates why, despite this potential, plasmonics rarely appear in top performing solar architectures. Three plasmonic enhancement pathways were experimentally proven: The metal nanoparticle can focus the incident sunlight, transfer a portion of its oscillating electrons, or share its energy non-radiatively through what is known as a coherence. The final mechanism was previously undiscovered, and through the quantum mechanical uncertainty of energy and time, allows the semiconductor to absorb sunlight at energies not otherwise possible. The efficiency of this process was measured to approach 90% and found to be tunable by changing how the electrons oscillated. Using these findings, a theoretical framework was created to optimize application of plasmonics. Based on this framework, several top performing solar-to-fuel devices were created which use sunlight to split water into hydrogen and oxygen. Additionally, the developed plasmonics technology is being incorporated into a commercial photovoltaic panel for turning sunlight into electricity.