Quantitative uniqueness of human brain evolution revealed through phylogenetic comparative analysis

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Abstract

While the human brain is clearly large relative to body size, less is known about the timing of brain and brain component expansion within primates and the relative magnitude of volumetric increases. Using Bayesian phylogenetic comparative methods and data for both extant and fossil species, we identified that a distinct shift in brain-body scaling occurred as hominins diverged from other primates, and again as humans and Neanderthals diverged from other hominins. Within hominins, we detected a pattern of directional and accelerating evolution towards larger brains, consistent with a positive feedback process in the evolution of the human brain. Contrary to widespread assumptions, we found that the human neocortex is not exceptionally large relative to other brain structures. Instead, our analyses revealed a single increase in relative neocortex volume at the origin of haplorrhines, and an increase in relative cerebellar volume in apes.

Data availability

All data used in our analyses are provided as supplementary material.

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Ian Forrester Miller

Ecology and Evolutionary Biology, Princeton University, Princeton, United States

For correspondence
ifmiller@princeton.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-2673-9618
Robert A Barton

Department of Anthropology, University of Durham, Durham, United Kingdom

Competing interests
The authors declare that no competing interests exist.
Charles L Nunn

Department of Evolutionary Anthropology, Duke University, Durham, United States

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-9330-2873

Funding

National Science Foundation (BCS-1355902)

Charles L Nunn

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.