Walkers or Tree Climbers? Early Humans Were Both
There has long been a belief among evolutionary anthropologists that our earliest ancestors could be either good climbers (like apes) or efficient walkers (like humans), but they couldn’t be both.
But recent research has thrown this either/or debate into question. In a groundbreaking analysis of fossils and biomechanics, Elaine Kozma, an anthropology doctoral student at The Graduate Center, CUNY, along with Professor Herman Pontzer and their team of researchers, discovered that the earliest hominins (think Lucy) had the bone and muscle structure to both walk upright and to climb trees.
The researchers found their answer in a 10-year journey led by Kozma that brought together several types of analyses including fossil measurements, anatomy research, and biomechanics, and finally by focusing on the pelvic bone, and more specifically the ischium, or sit bone.
What’s important about the ischium is its length and its angle. In chimpanzees, it’s long and angles down toward the feet. In humans, it’s short and angles more toward the back.
For this study, published in the Proceedings of the National Academy of Sciences, the researchers combined biomechanical analyses of hip extension during walking and climbing of living apes, humans, and monkeys with analyses of pelvic bone structures of the earliest hominins, including a 4.4-million-year-old Ardipithecus, the earliest hominin with a preserved pelvis, and Lucy, a younger Australopithecus (about 3.2 million years old).
The researchers found that although hominins had a long ischium, which gave them the power to climb, it was angled slightly back, which allowed them to walk upright and take longer strides. “The Ardipithecus was able to climb powerfully and walk efficiently, and we hadn’t thought that was possible before,” says Pontzer. “Because it had a long ischium, people thought it just walked like an ape,” he says. “This shows they were very efficient walkers, more similar to humans than to apes, but they didn’t give up their powerful climbing abilities.”
Explore This Work
Hip extensor mechanics and the evolution of walking and climbing capabilities in humans, apes, and fossil hominins
Proceedings of the National Academy of the Sciences, 2018
Elaine Kozma (Doctoral Student, Anthropology)
Herman Pontzer (Professor, Anthropology)