Babies: As we reported yesterday, they just keep getting bigger. And while they haven’t always been trending towards obese, human babies have always been larger, relative to their mothers, than the infants of most other species. This make birth difficult and could have even changed the social structure of early hominids, steering human evolution.
Human babies are about 6.1 percent of their mother’s weight at birth, while chimp babies are about 3.3 percent. A new paper published in the Proceedings of the National Academy of Sciences takes a look at our extinct relatives to determine when this shift occurred, and suggests that it could even have encouraged our ancestors to come down from the trees and to form more complex social arrangements.
As anthropologist Jeremy DeSilva of Boston Univeristy pointed out in his new paper, “carrying a relatively large infant both pre- and postnatally has important ramifications for birthing strategies, social systems, energetics, and locomotion.” [Scientific American]
The bones of our ancestors do not speak across time with ultimate clarity. The fossils with which scientists reconstruct our family tree are often fragments that offer hints and clues to where we came from. So it comes as no surprise when, as part of the flow of science, researchers offer counter-interpretations to even the most famous of finds.
That’s what happening to Ardi.
Last October Ardipithecus ramidus hit the main stage when, after 17 years of study, a large team led by paleoanthropologist Tim White published its work in the journal Science. The 4.4-million-year-old find shakes up our understanding of our own history, White said—primarily the story of how and when we learned to walk.
Ardi cast doubt on the widely accepted view that our ancestors became bipeds because they left the forest and entered a flatland savanna habitat that demanded it. But Ardi appeared to be a kind of hybrid, comfortable in the trees and on the ground. And, White said, analysis of the site where the fossil was found indicated that Ardi lived in a woodland habitat. If it’s true that early humans walked in the woods, then the “savanna hypothesis” would be swept away.
Humanity has a new matriarch: a hominid named Ardi who lived in Ethiopia 4.4 million years ago. Anthropologists have unveiled the results of 17 years of research on a new species named Ardipithecus ramidus, presenting a rich trove of fossils including the partial skeleton of the small-brained, 110-pound female. Ardi is 1.2 million years older than the famed “Lucy,” of the species Australopithecus afarensis, and experts say the find fundamentally changes our understanding of human evolution.
Study coauthor Tim White says that Ardi provides clues to what the last common ancestor shared by humans and chimps might have looked like before their lineages diverged about 7 million years ago…. But despite being “so close to the split,” says White, the surprising thing is that she bears little resemblance to chimpanzees, our closest living primate relatives [Time].
Ardi’s pelvis, leg, and feet bones indicated that she walked upright on two feet, but her opposable big toes suggest that she was also comfortable climbing trees. Her hand, arm, and shoulder bones indicate that she didn’t often swing through the trees, though; instead she probably walked on her palms along tree branches like some extinct apes. Based on Ardi’s anatomy, it appears that chimpanzees may actually have evolved more than humans — in the scientific sense of having changed more over the past 7 million years or so [Time].