Foot Fossils of Human Relative Illustrate the Evolutionary "Messiness" of Bipedal Walking
A new study on Homo naledi, the extinct human relative whose remains were discovered in a South African cave and introduced to the world last month, suggests that although its feet were the most human-like part of its body, H. naledi didn’t use them to walk in the same way we do. Detailed analysis of 107 foot bones indicates that H. naledi was well adapted for standing and walking on two feet, but that it also was likely comfortable climbing trees. The work, published in Nature Communications today with a concurrent study on H. naledi’s hands, provides insight into the skeletal form and function that may have characterized early members of our genus.
“Homo naledi’s foot is far more advanced than other parts of its body, for instance, its shoulders, skull, or pelvis,” said William Harcourt-Smith, lead author of the new paper, resident research associate in the American Museum of Natural History’s Division of Paleontology, and assistant professor at CUNY’s Lehman College. “Quite obviously, having a very human-like foot was advantageous to this creature because it was the foot that lost its primitive, or ape-like, features first. That can tell us a great deal in terms of the selective pressures this species was facing.”
Modern humans (Homo sapiens) and extinct species including Homo neanderthalensis, Homo erectus, Homo habilis, and Homo naledi are part of the Homo genus. The Homo genus and the Australopithecus genus (extinct, close relatives of Homo) are referred to as hominins.
Walking upright is one of the defining features of the human lineage, and as feet are the only structure that make contact with the ground in bipeds, they can tell us a lot about our ancient relatives’ way of moving. In the Dinaledi Chamber of the Rising Star cave system in South Africa, the H. naledi excavation team recovered at least one specimen from almost every single bone in the new species’ foot. These bones represent at least five individuals—two juveniles and three adults—including one nearly complete foot.
Analysis of these bones has shown that the foot bones look much more like human bones than chimpanzee bones, except for two major areas: the toes of H. naledi’s foot were more curved and their feet were generally flatter than seen in the average modern human. Despite the close similarity in the foot structure, H. naledi likely did not walk exactly like us, the researchers say. Clues from other parts of its body—long and curved fingers, and a more ape-like shoulder joint—paint a picture of a creature that was undoubtedly bipedal but also a tree climber.
“This species has a unique combination of traits below the neck, and that adds another type of bipedalism to our record of human evolution,” Harcourt-Smith said. “There were lots of different experiments happening within hominins—it wasn’t just a linear route to how we walk today. We are a messy lineage, and not just in our skulls and our teeth. We’re messy in the way we moved around.”
Because the H. naledi fossils have not yet been dated, researchers don’t know how this form of bipedalism fits into our family tree.
“Regardless of age, this species is going to cause a paradigm shift in the way we think about human evolution, not only in the behavioral implications—which are fascinating—but in morphological and anatomical terms,” Harcourt-Smith said.
Other authors include Zachary Throckmorton, University of Witwatersrand and Lincoln Memorial University; Kimberly Congdon, University of Witwatersrand and Southern Utah University; Bernhard Zipfel and Lee Berger, University of Witwatersrand; Andrew Deane, University of Witwatersrand and University of Kentucky College of Medicine; Michelle Drapeau, University of Witwatersrand and University of Montreal; Steven Churchill, University of Witwatersrand and Duke University; and Jeremy DeSilva, the University of Witwatersrand, Dartmouth College, and Boston University.
Funding was provided by the Leakey Foundation, Boston University, New York Consortium in Evolutionary Primatology, Lehman College CUNY, the National Geographic Society, and the South African National Research Foundation.
Nature Communications paper: http://dx.doi.org/10.1038/ncomms9432
American Museum of Natural History (amnh.org)
The American Museum of Natural History, founded in 1869, is one of the world’s preeminent scientific, educational, and cultural institutions. The Museum encompasses 45 permanent exhibition halls, including the Rose Center for Earth and Space and the Hayden Planetarium, as well as galleries for temporary exhibitions. It is home to the Theodore Roosevelt Memorial, New York State’s official memorial to its 33rd governor and the nation’s 26th president, and a tribute to Roosevelt’s enduring legacy of conservation. The Museum’s five active research divisions and three cross-disciplinary centers support approximately 200 scientists, whose work draws on a world-class permanent collection of more than 33 million specimens and artifacts, as well as specialized collections for frozen tissue and genomic and astrophysical data, and one of the largest natural history libraries in the world. Through its Richard Gilder Graduate School, it is the only American museum authorized to grant the Ph.D. degree and, beginning in 2015, the Master of Arts in Teaching degree, which began as a pilot in 2012 and is the only non-university affiliated such program in the United States. Annual attendance has grown to approximately 5 million, and the Museum’s exhibitions and Space Shows can be seen in venues on five continents. The Museum’s website and collection of apps for mobile devices extend its collections, exhibitions, and educational programs to millions more beyond its walls. Visit amnh.org for more information.
Become a fan of the Museum on Facebook at facebook.com/naturalhistory, follow us on Instagram at @AMNH, Tumblr at amnhnyc or visit twitter.com/AMNH to follow us on Twitter.