When it comes to understanding human evolution, the trove of fossils from South Africa that was unveiled last week offers much more than another potential new species. What’s raised the excitement level surrounding the finding is that it includes not just fragments of an individual or two but a whole population. There were males and females, infants, children and old people, with the promise of more bones to come.
“We’ve never had such a number of bones,” said University of Wisconsin anthropologist John Hawks, one of the scientists on the expedition. And never before has it been possible for so many researchers to instantly handle replicas of the bones, which are being downloaded and 3-D-printed around the world.
Within a few days of last week’s announcement, Kristina Killgrove, a University of West Florida anthropologist, had printed replicas of jawbones, teeth, and a skull of the upright-walking H. naledi. The expedition members made files available through a website called Morphosource.
Soon her students were able to use them to study the creature’s mysterious mix of humanlike and more primitive traits. “To me, this democratizes the process of paleoanthropology,” she says. “As far as I know this is completely unprecedented.”
Interested scientists and students will have plenty of questions to wrestle with, says Daniel Lieberman, a Harvard University paleoanthropologist who is familiar with the findings. The diverse array of individuals represented by these fossils could yield information about how long these people lived, and whether their Paleolithic diets added or subtracted from their life spans.
Also telling will be the so-called sexual dimorphism—size and anatomy differences between males and females. Males and females tend to look alike in more monogamous animals, which also tend to show more paternal care. Humans, for example, are less dimorphic than chimps and gorillas, and males of our species are more likely to help care for offspring. Some scientists see this difference as a crucial step in evolution of our comparatively large brains, but until now it’s been hard to know when and why we diverged in this way from our closest relatives.
What we know so far is that H. naledi’s body is a mosaic of traits – a relatively small brain, apelike shoulders, but a humanlike upright posture, feet, and hands. “There’s already a big debate about how primitive or modern the upper body is,” Lieberman says. The shoulders look like those of a creature adapted to climbing trees, but the feet suggest it walked the way we do. What’s mysterious, says Lieberman, is why we lost some of our tree-climbing prowess, since there’s no obvious reason why a creature can’t be well adapted to walk and climb.
One of the biggest questions scientists on the expedition have yet to answer is when H. naledi lived. This population may have existed quite recently and coexisted with our species, which originated about 200,000 years ago in Africa. Or they may go back much further. Many scientists consider our wider grouping – the genus homo – to define humanity. If the bones go back to the origin of our genus—around 2.5 million years—they may tell us something about the origin and evolution of humanity.
The scientists are expected to get some information from radiocarbon dating – a technique that relies on the steady rate of decay of a radioactive form of carbon after a plant or animal dies. But that technique can only get dates on material that’s been alive within the last 60,000 years, says Lieberman. If the skeletons are older, the team may be able to use other dating methods. Measuring the decay of uranium to lead in nearby limestone deposits can allow them to date materials that go back millions of years.
It’s interesting either way, though more informative if it’s old enough to have been a human ancestor. Whatever the age, the investigation will take place with unprecedented openness, thanks to the efforts of the expedition members to scan the fossils, says Lieberman. “I applaud them for this,” he says. “It should be the rule and not the exception.”