Humans said to have evolved hand control while still quadrupeds

Oct. 7, 2013 at 5:09 PM
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TOKYO, Oct. 7 (UPI) -- The question of what evolved first -- a dexterous hand or an agile foot -- has been solved, Japanese researchers say, and it's fingers over toes.

Early hominids developed finger dexterity and tool use ability before the development of bipedal locomotion, scientists at the RIKEN researcher institute reported Monday.

The findings contradict long-held assumptions that manual dexterity evolved only after the development of bipedal locomotion freed hominid hands to use fingers for tool manipulation, the said.

The researchers located the brain areas in both humans and monkeys responsible for touch awareness in individual fingers and toes, called somatotopic maps, and found that while monkey toes are combined into a single map, in humans the big toe has its own map not seen in monkeys.

This suggests early hominids evolved dexterous fingers when they were still quadrupeds, the researchers said, and while manual dexterity was not further expanded in monkeys, humans gained fine finger control and a big toe to aid bipedal locomotion.

This assumption was bolstered by analysis of the well-preserved hand and feet bones of a 4.4 million year-old skeleton of the quadruped hominid Ardipithecus ramidus, a species with hand dexterity that preceded the human-monkey lineage split.

"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 researchers wrote.

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