Modelling brain evolution


June 14, 2018

Three weeks ago in the journal Nature, researchers Mauriucio Gonzales-Fiorero and Andy Gardner proposed”… a metabolic approach that enables causal assessment of social hypotheses for brain-size evolution.”: The abstract of the authors’ paper states:

“The human brain is unusually large. It has tripled in size from Australopithecines to modern humans and has become almost six times larger than expected for a placental mammal of human size. Brains incur high metabolic costs and accordingly a long-standing question is why the large human brain has evolved. The leading hypotheses propose benefits of improved cognition for overcoming ecological, social or cultural challenges. However, these hypotheses are typically assessed using correlative analyses, and establishing causes for brain-size evolution remains difficult,. Here we introduce a metabolic approach that enables causal assessment of social hypotheses for brain-size evolution. Our approach yields quantitative predictions for brain and body size from formalized social hypotheses given empirical estimates of the metabolic costs of the brain. Our model predicts the evolution of adult Homo sapiens-sized brains and bodies when individuals face a combination of 60% ecological, 30% cooperative and 10% between-group competitive challenges, and suggests that between-individual competition has been unimportant for driving human brain-size evolution. Moreover, our model indicates that brain expansion in Homo was driven by ecological rather than social challenges, and was perhaps strongly promoted by culture. Our metabolic approach thus enables causal assessments that refine, refute and unify hypotheses of brain-size evolution.”

Dr Curtis Marean, Foundation Professor and associate director, Institute of Human Origins, School of Human Evolution and Social Change at Arizona State University comments,
“This is a really interesting paper, not so much for any specific conclusion (any of which must be preliminary due to the simplicity of the model), but more for the novelty of the approach.  All other studies have been correlative – trying to correlate brain size to other parameters to answer the question of “what caused brain size increases”.  This paper builds a model, albeit a simple one, and that allows one to start to manipulate the parameters to see effects.  One funny result is that expanded cooperation actually decreases brain size, but then that is consistent with some mammal groups.”

A colleague, Dr William H. Kimbel, and Director of the Institute of Human Origins, adds:
“…what I find intriguing about the conclusions—given the parameters of the model—is the emphasis on ecological (read: diet and feeding behavior) as opposed to social factors in explaining brain size increases.  This is in fact keeping with a growing number of correlational studies on animals as diverse as birds and primates that identify highly nutritious/patchily distributed/embedded or extracted food resources as more strongly linked to large brain size within clades than sociality.”

Read the full Nature paper.

In this same issue of 23 May 2018, there was commentary by Richard McElreath.