A chimpanzee and a human hold hands at an ape sanctuary in Brazil. New research suggests australopithecines' hands had a mix of ape and human traits. (Image credit: AFP Contributor via Getty Images)
Lucy and her fellow australopithecines may have created and used tools more than 3 million years ago, a new study of hand muscles suggests. The finding provides further evidence that tool use started long before the Homo genus emerged.
"While we can't definitively say that these early humans crafted stone tools, our findings demonstrate that their hands were frequently used in ways that closely align with the actions necessary for human tool manipulation," study co-author Fotios Alexandros Karakostis, a paleoanthropologist at the University of Tübingen in Germany, told Live Science in an email.
In a study published in the November issue of the Journal of Human Evolution, researchers examined muscle attachment sites on the hand bones of three australopithecine species and compared them with ape and human hands to try to understand when our ancestors gained the dexterity that modern humans have. Since australopithecines represent the chronological mid-point in the evolution of humans from ancient apes, the researchers suspected that australopithecine hand bones may also have traits of both apes and humans.
The researchers focused on hand entheses, which are places where tendons attach muscles to bones. When muscles and joints are used frequently, these attachment sites adapt, resulting in a pattern of bony changes that suggest specific habitual activities.
"By studying these muscle attachment sites, we can reconstruct how muscles and ligaments were actively engaged throughout life, giving us a clearer picture of early hominin behavior," Karakostis said.
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Muscle attachment sites on the hands of three australopithecine species revealed that they were all likely able to manipulate objects. But the comparatively recent hominin Australopithecus sediba (1.95 million to 1.78 million years ago) had a more humanlike hand than did the more ancient A. africanus (3.7 million to 3.4 million years ago) and A. afarensis (3.7 million to 3 million years ago), which both had a mosaic of humanlike and apelike traits.
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Although apes can grasp and manipulate objects, their dexterity in these tasks is limited by their hand anatomy. Homo sapiens, meanwhile, have two key anatomical features that are essential to the ability to precisely grasp, grip and pinch objects, the researchers found.
The first dorsal interosseus muscle is located in the palm between the thumb and index finger and lets us precisely pinch things. "This unique functionality provided early hominins with the dexterity needed to manipulate objects -- including tools -- effectively, paving the way for both technological and cultural progress," study first author Jana Kunze, a paleoanthropologist at the University of Tübingen, said.
The pinky finger also plays a crucial role in humanlike grasping, the researchers noted. Early hominins like A. afarensis and A. sediba probably relied on pinky muscles for essential daily tasks such as handling tools and preparing food.
"More broadly speaking, the co-evolution of the thumb and pinky were decisive for hominin biocultural evolution, setting the stage for the advanced humanlike dexterity we see in humans today," Kunze said.
The question of how dexterous australopithecines' hands were is directly tied to the question of which species first made and used tools. When Homo habilis was discovered in the 1960s, scientists named it "handyman" because it was found with very old stone tools dating back 2.3 million years. For many years, researchers assumed australopithecines did not have the mental or physical capacity to make tools. But the 2015 discovery of 3.3 million-year-old tools at a site called Lomekwi in Kenya raised the controversial possibility that A. afarensis made them.
"Our study indicates that Australopithecus afarensis -- the species Lucy belonged to -- frequently performed humanlike grasping patterns, using their hands in ways that suggest regular, skilled manipulation of objects within the hand," Karakostis said. However, "these findings don't directly show that A. afarensis or A. sediba made or used stone tools in particular."
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Tracy Kivell, director of Human Origins at the Max Planck Institute for Evolutionary Anthropology who was not involved in the study, told Live Science in an email that this muscle attachment research is novel and interesting, showing that each species interacted with its environment in different ways, including their manipulative abilities.
"It is likely that each of these australopiths were using tools and climbing," Kivell said, and the muscle attachment sites "provide exciting information about how these particular australopith individuals were using their hands during life."