![]() ![]() ![]() Since monkey and human manual dexterity as well as their finger-to-brain maps were similar, the team believes they reflect a common ancestral toolkit. As in humans, monkeys can use the thumb both in precision grips, such as pinching an object between the tip of the thumb and other fingers, and in power grips. By contrast, monkeys dorsiflex their hands and place their palms and/or extended fingers on the ground or branch during quadrupedal walking. In chimpanzees (and bonobos and gorillas), the backs of the middle fingers contact the ground (or large branches) during quadrupedal knuckle-walking. Rather, the chimpanzee hand is elongated and hook-like, and effective in hanging from trees. Monkeys can use tools as an extension of their arms, whereas chimpanzees lack tool-related grips, such as forceful gripping, precision handling and power squeezing, owing to their long fingers and short thumbs. 3Įxplaining the importance of each finger having its own unique map on the brain, as well as their choice of the monkey to study, the researchers write: Fine somatosensory resolution is critical to hand dexterity, because the sensory feedback from fingers contributes to adaptive precision grip. Hashimoto et al., via Philosophical Transactions B. A Tokyo team of researchers has concluded, after comparing brain-maps of these hands and feet, that humans evolved their terrific manual dexterity without waiting for balanced bipedal gait to evolve and free up their hands. Unlike these appendages, the human foot has a big toe for balance instead of an opposable thumb-like first digit. The Japanese macaque ( Macaca fuscata) has hands and feet that look and function much like human hands. Thus each finger sends sensory information to a particular spot on the brain and receives instructions for independent movement. ![]() They found that, in both in monkeys and humans, each finger maps to a discrete region on the brain’s cortex. Using magnetic resonance imaging for humans and electrophysiological recordings for monkeys, the team mapped the brain location stimulated by touching each digit. Neurobiologist Iriki says, “ Evolution is not usually thought of as being accessible to study in the laboratory, but our new method of using comparative brain physiology to decipher ancestral traces of adaptation may allow us to re-examine Darwin's theories.” Therefore, the Tokyo team picked the Old World monkey to help them study human hand evolution. The monkey has hands-and even feet-very similar to human hands (see illustration). Chimpanzee hands are specialized for arboreal life and confuse the picture, creating what the authors call “the riddle of man’s ancestry.” 2 The Old World monkey is thought to have diverged from the ape-ancestral line before the supposed human-chimp split. In order to get a handle on the evolutionary history of the human hand, the team chose to use an Old World monkey-a macaque-rather than a chimpanzee. Contrary to the ‘hand-in-glove’ notion outlined above, our results suggest that adaptations underlying tool use evolved independently of those required for human bipedality. In this study, we sought to shed new light on the origins of manual dexterity and bipedalism by mapping the neural representations in the brain of the fingers and toes of living people and monkeys. Either way, it is commonly thought that one led to the other. Neurobiologist Atsushi Iriki, anthropologist Gen Suwa, and colleagues write: People have long speculated whether the evolution of bipedalism in early hominins triggered tool use (by freeing their hands) or whether the necessity of making and using tools encouraged the shift to upright gait. In answer to the question of which came first-better hands or better feet-the University of Tokyo team says, “Neither!” Which Came First? But how could coming down from the trees and walking on two legs provide the evolutionary incentive for hominid brains to grow? Did hands finally free to use tools promote hominid brain evolution or did the necessity of using tools make bipedal locomotion the only way to go further up the evolutionary ladder?Ī study published this month in Philosophical Transactions of the Royal Society B reports that brain-mapping data on monkeys and humans resolves this debate. It was generally easier to claim that small-brained extinct fossilized apes were bipedal than that they had big brains, so the bipedal position won out. Once upon a time, the proponents of human evolution debated about which came first-big brains or bipedal locomotion. Science Daily: “ What Evolved First, a Dexterous Hand or an Agile Foot?”. ![]()
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