Recent research calls into question previous assumptions about what brain size means. For example, brain size is generally considered a proxy for complex cognition, however new research shows that the number of neurons in a brain does not linearly scale with brain size across mammals or birds. Neurons are the substrate on which cognition occurs, therefore it now appears more appropriate to consider cognitive abilities in the context of neuron number rather than brain size. These results call into question what brain size actually measures, what previous results based on brain size mean, how we should use this metric in the future, and what we should measure instead.

Suzana Herculano-Houzel is neuroscientist in the Laboratory of Comparative Anatomy of the Federal University of Rio de Janeiro in Brazil. She is interested in particular in studying the relationship between brain size and the number of neurons.

Corina Logan is a comparative psychologist and zoologist at the department of Zoology of Cambridge University. Corina is interested in the evolution of brain size, behavioural flexibility, and complex cognition using lab and field experiments.