Mosaic evolution and increased integration underpin the evolvability of the dog brain

How the brains of domestic animals evolved under domestication remains poorly understood. We quantified brain shape variation in domestic dogs (n = 203, 111 breeds) and wolves (n = 40) using endocast-based 3D geometric morphometrics. Size, shape, and morphological integration were assessed on the whole brain, and in six morphofunctional subregions. Results demonstrate that domestication and artificial selection significantly restructured brain form and morphological integration patterns in dogs, reflecting mosaic evolution across brain subregions. Dogs exhibit a three-fold increase in brain shape variation relative to wolves, as well as expanded frontal lobes and areas putatively associated with social interaction behavior-these regions are also larger in cooperative vs. independent breeds. Morphological integration is higher in dogs than wolves, and in modern breeds compared to ancient breeds. Thus, rather than constrain, integration appears to facilitate neuroanatomical evolvability under domestication and breeding selection. Ancient dog breeds retain more wolf-like neuroanatomy. Breed function is a poor predictor of brain shape, but brain integration restructures according to breed function, with working breeds displaying the highest integration. These findings reveal the profound impact of domestication on neuroanatomical evolution, emphasizing neuroanatomical features linked to social behavior, and challenging prevailing assumptions about the role of structural integration on evolvability.