![]() Twenty percent of figs show no color change during ripening, which poses a sensory challenge. Ripe figs are almost always available when other fruits are scarce, so animals depend on them at these crucial periods.” “They’re not a particularly high-quality fruit, but in a given area, individual trees ripen at different times. “Figs are critically important,” Dominy says. It means chimps can forage more efficiently and consume more calories, especially during lean times when preferred foods are unavailable and they are forced to rely on figs. That speed can make all the difference when animals are competing for limited resources, Dominy says. What’s more, squeezing a fig is four times faster than plucking it, biting it and spitting it out if it was not ripe.Ĭhimpanzee in Kibale National Park, Uganda, squeezing a fig to test its ripeness. Monkeys that compete for the same food must rely on color and bite testing, but squeezing figs by chimpanzees supplies nearly 75 percent more information about ripeness than color. It’s fair for researchers to look at complex hand use among primates and ask if it was a precursor to the manual dexterity that gave rise to modern humans.”īased on field work in Uganda, Dominy and Peter Lucas, researcher at the Smithsonian Tropical Research Institute, who served as one of the study’s co-authors, determined a chimpanzees’ ( Pan troglodytes) ability to feel the ripeness of a fig confers a significant advantage over rival species when selecting fruit. “Hands are a hallmark of human evolution. A surprising omission, he believes, given the importance of hand dexterity and tool use to human development. “We anthropologists have given little thought to why ape hands have greater dexterity than monkey hands,” says Nathaniel Dominy, evolutionary biologist at Dartmouth and lead author of the new study. This video shows a chimpanzee in Uganda evaluating figs (Ficus sansibarica ). Now, a new study published in the journal Interface Focus sheds light on how increased finger dexterity and sensitivity may have benefited the diets of early apes, allowing them a competitive edge in obtaining high-quality food. The additional brain power needed to operate dexterous hands called for a lot of nutritious, high-calorie food as well. Humans stand out as the only hominid with fully opposable thumbs that can turn in toward the palm to touch the tip of each finger.ĭeveloping such complex hands was a costly evolutionary feat, requiring not only anatomical changes to the wrist and fingers, but also expanded nervous tissue to process sensory and motor signals between fingers and brain. One of the primary features that distinguish hominids such as chimpanzees, gorillas and humans from the rest of the animal kingdom are uniquely dexterous hands. The researchers also identified examples of convergent evolution - in which similar traits develop independently in different lineages - including finger elongation in both chimpanzees and orangutans, and high thumb-to-finger ratios among human ancestors and “other highly dexterous anthropoids such as capuchins and gelada baboons.A chimpanzee in Kibale National Park, Uganda, bites a fig. The results, reported in Nature Communications, show that the finger and thumb lengths of human hands have actually changed little since the human-chimp LCA, countering the notions that the LCA’s hands were more chimp-like and that higher thumb-to-finger ratios only emerged in later human ancestors. Combining the data with phylogenetic models, they pieced together a map of evolutionary change in primate hands. Sergio Almécija of Stony Brook University in New York and colleagues made detailed measurements of hand proportions among humans, apes and other living primates, as well as of fossil species like the primitive African ape Proconsul heseloni and the early human ancestors Ardipithecus ramidus and Australopithecus sediba, noting a wide range of hand dimensions among modern hominoids. But rather than humans having the more evolved hand - a prevailing hypothesis since the late 20th century - a new study suggests that chimps' hands, with lower thumb-to-finger-length ratios, have changed considerably more. This trait has endowed our ancestors and us with a particular talent for grasping and working with tools, which likely contributed to our evolutionary success over the last several million years since splitting off from the last common ancestor (LCA) shared by the two groups. Credit: Almécija et al., Nature Communications, 2015, CC BY 4.0.Ĭompared to chimpanzees, our recent evolutionary cousins, humans have long thumbs relative to our fingers. With longer fingers, chimpanzees have lower thumb-to-finger-length ratios than humans.
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