New Research Challenges Old Evolutionary Theories

Researchers are re-examining Darwin's evolutionary theories with new work published in the journal Philosophical Transactions of the Royal Society, which suggests that early hominids evolved dexterous fingers and the ability to use tools before the ability to walk upright on two legs, a find that overturns the commonly held belief that manual dexterity came after bipedal locomotion.

Researchers from the RIKEN Brain Science Institute in Japan explored the concept by a combined analysis of human and monkey behavior, plus brain imaging and fossil evidence.

Neurobiologist Atsushi Iriki and Gen Suwa, an anthropologist from the University of Tokyo Museum, led the research, which sought to locate brain areas responsible for touch awareness in fingers and toes. These areas are known as somatotopic maps. By using the somatotopic maps, the researchers were able to confirm that individual digits in the hand and foot have discrete neural locations in both humans and monkeys.

The research team uncovered new information on the toes of humans and monkeys. Monkey toes are combined into a single somatotopic map, just like human toes. But unlike the monkeys, humans' big toe has its own map, the researchers learned.

"These findings suggest that early hominids evolved dexterous fingers when they were still quadrupeds. Manual dexterity was not further expanded in monkeys, but humans gained fine finger control and a big toe to aid bipedal locomotion," the authors explained in a statement.

"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," they continued.

The researchers also analyzed well-preserved hand and foot bones of an ancient skeleton of the quadruped hominid Ardipithecus ramidus. The 4.4-million year-old specimen had hand dexterity that predated the human-monkey linage split, the researchers said.

The find suggests "parallel evolution of two-legged locomotion and manual dexterity in hands and fingers in the human lineage were a consequence of adaptive pressures on ancestral quadrupeds for balance control by foot digits while retaining the critical capability for fine finger specialization," the researchers said.