A Canine Window into Human Evolution: Brain Morphology, Asymmetry, and Plasticity

Abstract

Understanding how brains evolve requires a system in which selective history, brain size and structure, skull morphology, and behavioral specialization can be measured directly, dissociated from one another, and compared across differentiable lineages. The domestic dog (Canis familiaris) provides exactly this. Through a combination of natural and artificial selection, dogs have evolved extraordinary variation in skull morphology, brain anatomy, and behavior within a single species, and they can be studied using the same neuroimaging methods applied to humans. In this dissertation, I use dogs as a living model system to test biological principles of brain evolution that are directly relevant to the human lineage. In Chapter 2, I show that variation in skull shape significantly predicts regional gray matter volume, demonstrating that selection on skull morphology can reshape brain organization. In Chapter 3, I characterize widespread neuroanatomical asymmetry in the canine brain and find that lateralization does not scale with brain size, suggesting it is not simply a byproduct of encephalization but may instead reflect selection on lateralized behaviors. In Chapter 4, I compare modern breed dogs, which were intensively selected for cooperative learning, with premodern dogs that underwent far less artificial selection. Modern breeds show cortical expansion linked to trainability, while premodern dogs show amygdala enlargement linked to fear. In Chapter 5, I extend this comparison to white matter and find that modern breeds exhibit greater fractional anisotropy, altered connectome topology, and fractional anisotropy patterns that predict trainability. In Chapter 6, I compare Labrador retrievers that vary in breeding lineage and training history and find evidence for experience-dependent plasticity in working dogs but no innate neuroanatomical differences between non-working dogs from different lineages, suggesting that selection may favor neuroplasticity itself rather than canalization of specific skills. Altogether, this dissertation demonstrates that even over short evolutionary timescales, selection can substantially reshape brain structure, and that the domestic dog offers a powerful window into the principles governing brain evolution in species that shares our anthropogenic niche.