From Fossils To Mind Workshop 2021: Orlin S. Todorov

Evolution of the mammalian brain: using phylogenetic comparative methods to study brain evolution in three mammalian clades

Orlin S. Todorov


The University of Queensland, School of Biological Science


Studying the evolution of brains using phylogenetic comparative methods (PCMs) hasa multitude of methodological and conceptual challenges – from the scale of inquiry to the actual methodological approaches, and hypotheses being tested. Aims and Methods I address the evolution of brain size variation in three clades of mammals – primates (order), marsupials (infraclass) and leporids (family) – and at different scale of inquiry – whole brains, brain lobes, and sub-regions of brain areas. In addition, as the choice of analytical methods I am applying both a classical pGLS (phylogenetic generalized least squares regression) and Bayesian GLMM (generalized linear mixed model) approach.

As an additional innovation I address one of the pervasive methodological issues in PCM studies by dealing with missing data. Instead of using the traditional method of list-wise deletion I explore the utility of a novel phylogenetic method for multiple imputation. Results Different levels of inquiry yield different results, that are nonetheless informative, and thus the scale of brain size variation should be carefully scrutinized in respect to the actual questions being asked. Addressing questions at the level of larger clades risks masking effects that are at work in smaller taxonomic groups. Additionally, different methodological frameworks provide different advantages and disadvantages for data analysis.