Nov. 13 (UPI) -- New research suggests it wasn't superior intelligence that set our earliest pre-human ancestors, like Australopithecus, apart from apes.
For the study, scientists analyzed holes in the skull that allow the passage of supply arteries to the brain, calculating blood flow to the cognitive part of the brain. Researchers calibrated their estimates using humans and other mammal models, and then applied their calculations to 96 great ape skulls and 11 Australopithecus fossil skulls.
The data -- published Wednesday in the journal Proceedings of the Royal Society B -- showed modern apes benefit from greater blood flow to their brain's cognitive regions than Australopithecus.
Australopithecus, the species responsible for the famed "Lucy" fossil, had a larger brain than apes. Anthropologists have long assumed larger brains yielded greater cognitive functionality and superior intelligence, but the latest findings suggest otherwise.
"At first, brain size seems reasonable because it is a measure of the number of brain cells, called neurons," Roger Seymour, professor of biological sciences at the University of Adelaide in Australia, said in a news release. "On second thought, however, cognition relies not only on the number of neurons, but also on the number of connections between them, called synapses. These connections govern the flow of information within the brain and greater synaptic activity results in greater information processing."
Synaptic activity fuels the human brain's powerful cognitive abilities, and synaptic activity requires a lot of energy and significant blood supply. The human body has evolved to deliver 15 to 20 percent of its energy to the brain. Additionally, 15 percent of the blood pumped by the heart is directed to the brain.
Through the years, apes have proven capable of impressive cognitive feats. The famous gorilla Koko learned sign language, comprehending more than 1,000 signs. Kanzi, a bonobo, learned English comprehension and syntax, and also built stone tools.
With a brain equal to and bigger than such apes, researchers assumed Lucy and her relatives were smarter.
"It is known that the large human brain looks like a scaled-up primate brain in terms of size and neuron number," Seymour said. "However, the study shows that cerebral blood flow rate of human ancestors falls well below the data derived from modern, non-human primates."
The latest research suggests great apes like Koko received about twice as much blood flow as Lucy to the cerebral hemispheres.
"Because blood flow rate might be better measure of information processing capacity than brain size alone, Koko seems to have been smarter," Seymour said.