A major focus of evolutionary neurobiology has been on whether different regions of the eutherian
brain evolve in concert, and how free the brain is to evolve independently of body plans. Since the
eutherian brain is loosely modularized, such that one region is rarely isolated for specialization at the
expense of others, but the design of modularization itself can be adapted by tweaking developmental
programs, the degree to which brain regions must evolve in concert and can evolve independently may
carry a deep phylogenetic signal. Using data collected from preserved brain tissue of 37 primate, 21
carnivore, and 15 other eutherian species (spanning 11 orders), I examined the phylogenetic level at
which the proliferation of neurons and glia in the primary visual cortex and hippocampus proper, as
well as granular layer volumes of the dentate gyrus and cerebellum, may be constrained by conserved
developmental programs. In doing so, I was able to test for cellular signatures of (1) evolutionary
changes in metabolic activity, (2) phylogenetic divergences, (3) specializations in behavior, and (4)
developmental constraints. The degree to which disparate brain regions evolve in concert is shown to
be generally conserved in Eutheria, although a derived ability to evolve regions independently is
observed along the primate lineage. Using a separate dataset on placental and life-histroy character
states, a comprehensive comparative phylogenetic approach was used to resolve relationships among
five aspects of placental structure and to identify syndromes of placental morphology with life-history
variables. My results support two discrete biological phenotypes of placental morphology and life-history,
which are shown to have an evolutionary affect on allocortical, but not neocortical, brain
organization. I have provided a new perspective on exploring how developmental constraints – acting
both within and without the brain – may affect brain organization at the cellular level, and the extent to
which those constraints have been adapted along certain eutherian lineages