The evolution of the complex sensory and motor systems of the human brain.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing comparative neuroanatomy and fossil endocast data
PubMed 18331903 · doi:10.1016/j.brainresbull.2007.10.009
What was done
This narrative review synthesized evidence on the evolution of human sensory and motor systems by combining comparative neuroanatomical studies across living mammalian species (representing the six major mammalian branches) with fossil endocast evidence from extinct species.
What was found
Early mammalian brains were small with limited neocortex divided into approximately 20 to 25 cortical areas, including primary and secondary sensory fields. In early primates, vision expanded to 10 or more visual areas in temporal and occipital cortex, somatosensory forepaw representations enlarged, and the posterior parietal cortex expanded with rostral (somatosensory) and caudal (visual) subdivisions projecting to 7 or more frontal motor and visuomotor areas. Further differentiation occurred in anthropoid primates, culminating in an estimated ~200 cortical areas and hemispheric specializations in modern humans. The human brain expanded primarily via an increase in total neuron number rather than increased average neuron size.
Why it matters
It provides a comparative evolutionary framework explaining how human cognitive, sensory, and motor complexity arose through progressive cortical arealization and increased neuron counts rather than cellular hypertrophy.
Limits
As a narrative review, the abstract provides no specific sample sizes, species counts, or quantitative statistical comparisons. Inferences rely on indirect reconstruction using fossil endocasts and living proxy species rather than direct observation of ancestral soft tissue.
Cited by
- supports Humans have more distinct sensory cortical areas than monkeys and more distant mammalian relatives.