title: Fossil skulls reveal that blood flow rate to the brain increased faster than brain volume during human evolution.
abstract: The evolution of human cognition has been inferred from anthropological discoveries and estimates of brain size from fossil skulls. A more direct measure of cognition would be cerebral metabolic rate, which is proportional to cerebral blood flow rate (perfusion). The hominin cerebrum is supplied almost exclusively by the internal carotid arteries. The sizes of the foramina that transmitted these vessels in life can be measured in hominin fossil skulls and used to calculate cerebral perfusion rate. Perfusion in 11 species of hominin ancestors, fromAustralopithecusto archaicHomo sapiens, increases disproportionately when scaled against brain volume (the allometric exponent is 1.41). The high exponent indicates an increase in the metabolic intensity of cerebral tissue in laterHomospecies, rather than remaining constant (1.0) as expected by a linear increase in neuron number, or decreasing according to Kleiber's Law (0.75). During 3 Myr of hominin evolution, cerebral tissue perfusion increased 1.7-fold, which, when multiplied by a 3.5-fold increase in brain size, indicates a 6.0-fold increase in total cerebral blood flow rate. This is probably associated with increased interneuron connectivity, synaptic activity and cognitive function, which all ultimately depend on cerebral metabolic rate.
authors.affiliation: School of Biological Sciences , University of Adelaide , Adelaide, South Australia 5005 , Australia.
authors.forename: Roger S
authors.identifier: 0000-0002-3395-0059
authors.initials: RS
authors.lastname: Seymour
authors.affiliation: School of Biological Sciences , University of Adelaide , Adelaide, South Australia 5005 , Australia.
authors.forename: Vanya
authors.initials: V
authors.lastname: Bosiocic
authors.affiliation: Brain Function Research Group, School of Physiology , University of the Witwatersrand , Johannesburg, Gauteng 2193 , South Africa.
authors.forename: Edward P
authors.identifier: 0000-0002-8985-8737
authors.initials: EP
authors.lastname: Snelling
keywords: brain perfusion; cerebral cortex; cognition; evolution; hominin