Today's Great Apes Are Probably Brainier Than Our Pre-Human Ancestors

The great apes alive today outperform pre-humans in the brain department. That's according to research published in the Proceedings of the Royal Society B on Wednesday.

The findings challenge traditional assumptions that the larger-sized brain of Lucy and others of the pre-human species Australopithecus implies they were smarter than the great apes of today, a group that includes gorillas, orangutans and chimpanzees.

"[It] has been generally assumed that intelligence is directly related to the size of the brain," lead author Roger Seymour, a professor in the School of Biological Sciences at Australia's University of Adelaide, said in a statement.

The research was conducted by scientists at the University of Adelaide alongside academics at the University of the Witwatersrand in South Africa, and centered on the rate of blood flow to areas of the brain associated with cognition. This was measured via the size of the holes in various skulls that would have connected the internal carotid artery to the brain—a technique that has been validated by the study of blood flow and holes in the skulls of humans and other mammals (including mice and rats), the researchers say.

"At first, brain size seems reasonable because it is a measure of the number of brain cells, called neurons," said Seymour.

"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."

Lucy the Australopithecus
A sculptor's rendering of the hominid Australopithecus afarensis at an exhibition in the Houston Museum of Natural Science. New research suggests they weren't as brainy as modern great apes. Dave Einsel/Getty

The human brain, for example, spends 70 percent of its energy on synaptic activity.

"It is known that the large human brain looks like a scaled-up primate brain in terms of size and neuron number. However, the study shows that the cerebral blood flow rate of human ancestors falls well below the data derived from modern, non-human primates," said Seymour.

The researchers found that great apes like Koko the gorilla, who learned to communicate using sign language (and more than 1,000 signs), had an estimated rate of blood flow that was approximately twice the size of Lucy's—suggesting she and other great apes are smarter than our 3-million-year-old ancestor. According to the Smithsonian Museum of Natural History, Australopithecus, like Lucy, inhabited Eastern Africa in areas in what is now Ethiopia, Kenya and Tanzania.

"Because blood flow rate might be a better measure of information processing capacity than brain size alone, Koko seems to have been smarter," said Seymour.

brain scan
A brain scan. The human brain occupies 2 percent of body weight but uses between 15 and 20 percent of our energy. Fred TANNEAU / AFP/Getty