The evolution of the frontal lobes: a volumetric analysis based on three-dimensional reconstructions of magnetic resonance scans of human and ape brains.
Level 5 - mechanism / opinion, no new human data
Level is by design analogy, not clinical CEBM: comparative morphometric study using animal and post-mortem specimens alongside living humans.
PubMed 9085187 · doi:10.1006/jhev.1996.0099
What was done
The authors measured the volume of the total frontal lobe and its principal sectors (dorsal, mesial, and orbital, encompassing cortex and immediately underlying white matter) using three-dimensional reconstructions of magnetic resonance imaging (MRI) scans. Scans were obtained from living humans and post-mortem brains of chimpanzees, gorillas, orangutans, gibbons, and macaques.
What was found
The abstract reports no numerical volumetric values or statistical metrics. Qualitatively, although absolute brain and frontal lobe volumes were largest in humans, the relative proportion of the frontal lobe and its major sectors was similar across all hominoid species examined, indicating the human frontal lobe is not larger than expected for an anthropoid primate of human brain size.
Why it matters
This study challenges the hypothesis that human-specific cognitive capabilities arose primarily from disproportionate volumetric enlargement of the frontal cortex relative to the rest of the brain.
Limits
The abstract does not provide exact sample sizes (noted by authors as remaining small), exact measurements, confidence intervals, or statistical tests. It compares in vivo human MRI scans with post-mortem ape brains, introducing potential tissue fixation and processing artifacts.
Cited by
- contradicts The relative size of the human prefrontal cortex is uniquely large compared to close animal relatives.