According to a news release from the RIKEN Brain Science Institute, early hominids evolved finger dexterity and tool use ability before the evolution of bipedal locomotion. RIKEN researchers contend that their findings identify a solution to a long-lasting puzzle in human evolution.

Researchers analyzed monkey and human behavior, brain imaging and fossil evidence to discredit the common belief that hand control development after the evolution of bipedal locomotion liberated hominid hands to utilize fingers for tool use.

The researchers turned to functional MRI in humans and electrical records from monkeys to find the brain areas responsible for touch alertness in individual fingers and toes, known as somatotopic maps. The researchers used these maps to validate earlier research revealing that single digits in the hand and foot have separate neural areas in both humans and monkeys.

However, the researchers discovered new evidence that monkey toes are combined into a single map, while humans toes are also combined into a single map, but with the important exemption of the big toe, which has its own map not observed in monkeys. These results imply that early hominids developed dexterous fingers when they were still quadrupeds. Hand control was not further honed in monkeys, but humans evolved fine finger control and a large toe to help with bipedal locomotion.

“In early quadruped hominids, finger control and tool use were feasible, while an independent adaptation involving the use of the big toe for functions like balance and walking occurred with bipedality,” the authors said.

The findings were validated by the examination of the hand and feet bones of a 4.4 million year-old skeleton and the quadruped hominid Ardipithecus ramidus, a species with hand nimbleness that predated the human-monkey lineage split.

The results imply that the parallel development of bipedal locomotion and manual aptness in hands and fingers in the human lineage were a result of adaptive pressures on ancestral quadrupeds for balance control by foots digits while keeping the crucial capacity for fine finger specialization.

“Evolution is not usually thought of as being accessible to study in the laboratory,” noted neurobiologist Dr. Atsushi Iriki, “but our new method of using comparative brain physiology to decipher ancestral traces of adaptation may allow us to re-examine Darwin’s theories.”

The study’s findings are described in detail in the journal Philosophical Transactions of the Royal Society.