Washington, Oct 8: Early hominids may have developed finger dexterity and tool use ability before bipedal locomotion was developed in them, a new study has suggested.
Combining monkey and human behavior, brain imaging, and fossil evidence, a research team led by neurobiologist Dr. Atsushi Iriki and including Dr. Gen Suwa, an anthropologist from the University of Tokyo Museum, have overturned the common assumption that manual dexterity evolved after the development of bipedal locomotion freed hominid hands to use fingers for tool manipulation.
In the study, the researchers employed functional magnetic resonance imaging in humans and electrical recording from monkeys to locate the brain areas responsible for touch awareness in individual fingers and toes, called somatotopic maps.
With these maps, the researchers confirmed previous studies showing that single digits in the hand and foot have discrete neural locations in both humans and monkeys.
However, they found new proof that monkey toes are combined into a single map, while human toes are fused into a single map, but with the prominent exception of the big toe that has its own map not seen in monkeys.
These findings suggest that early hominids evolved dexterous fingers when they were still quadrupeds.
The brain study was supported 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.
The findings suggest that the 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 study has been published in Philosophical Transactions of the Royal Society. (ANI)