New research from the RIKEN Brain Science Institute indicates that, contrary to current belief, early hominids developed finger dexterity before they became bipedal. The long-standing theory that bipedalism "freed up" the proto-human hand for using tools has been overturned by brain imaging and fossil evidence that indicates that the quadruped brains possess the same potential for manual dexterity as human.
"Evolution is not usually thought of as being accessible to study in the laboratory", stated Dr. Iriki, one of the researchers, "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 researchers found that monkey toes were combined into a single "somatotopic map," which indicates the location in the brain responsible for "touch awareness" in fingers and toes. Human toes are also fused into a single map, with the exception of the big toe, which has its own map. This suggests that proto-humans gained fine motor control over their fingers when they were still quadrupeds.
"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 wrote.
That thumbs and big toes evolved in a parallel fashion indicates that both were the consequence of adaptive pressures, instead of the latter creating the conditions in which the former could evolve.