14

Because we had found a new species, we needed to give it a name. Taking a break from looking at the fossils, I played around with the Sesotho dictionary on my laptop, trying out words that might have meaning for either the fossils or the site. Occasionally I would speak one out loud for the group who were there, silently working on the fossils. They developed a ritual—thumbs down, not even looking up as they expressed dissatisfaction with one name after another.

Finally, I looked for the Sesotho word for “spring,” as in a source of water. We suspected that the Malapa site might have been a water source that had attracted these hominins and other animals, causing them to fall to their deaths. In Sesotho, the word for “spring” also means “wellspring,” “fountain,” or “source”: sediba.

I said the word out loud and everyone stopped and looked at me. “I like it. What does it mean?” asked Darryl.

I explained the meaning. First Job then each of the others nodded in agreement.

“At least a BBC presenter won’t mispronounce it!” I said, only half-joking. We had our name: Australopithecus sediba.

We made the first public announcement of the new species in April 2010, in the august journal Science. Our announcement describing the fossils noted them as representing a new Homo-like species of Australopithecus. The scientific work showed in detail the mosaic nature of sediba’s anatomy—features seen in several other known hominin species yet never in this combination—and how it appeared to represent a transition between more primitive australopiths and the earliest members of the genus Homo. It was a time of celebration for everyone involved in the discovery, as the work received headlines around the world. Twenty months after Matthew had shouted, “Dad, I found a fossil!” we had now published the first scientific description of two partial skeletons of a new hominin species.

We could not be sure exactly how sediba was related to humans on our family tree. Our study of the features of the skull, jaws, and teeth made it clear that sediba was very close to the branch that led to Homo. That branch included not only extinct species like habilis and erectus, but modern humans too. Its similarities to these species made it possible that something like sediba might have actually given rise to our genus. Certainly we could not rule it out. Neither could we rule out that sediba had evolved for a long time in parallel with Homo. The common ancestor of the two forms might be very different from either.

Science journalists sometimes treat human evolution like a horse race, describing how different fossil discoveries are jockeying for a position as the true ancestor of humanity. It is a tendency that goes back to the Taung Child discovery and even earlier, a mistake sometimes made by scientists as well as journalists. We could not dismiss the possibility that sediba might be an ancestor of Homo, and this proved controversial. Other scientists had claimed much earlier evidence of Homo, or Homo-like relatives, dating back to 2.5 million years ago or even more. This was earlier than the geological age of the Malapa skeletons, which were only around two million years old. To some scientists, the age of the skeletons was enough to answer the question by itself. Sediba might look like a human ancestor in some ways, but it was just too recent. This was a simple argument, the idea that ancestors must be older than their descendants. But in fact, we didn’t know how old sediba might be; we only knew how old the Malapa skeletons were. The species existed for some time, and the evidence didn’t say when that time started or ended.

What we could say was that sediba’s anatomy was an unexpected mosaic, and that had big consequences for the way we understood the origin of Homo. Even the most exceptional skulls of habilis and rudolfensis fossils had no arms or legs accompanying them. What little anyone thought they knew about the rest of the habilis skeleton, it looked like an australopith, and no one had ever found a rudolfensis skeleton. Most scientists called these skulls Homo because they had a slightly bigger brain than most australopiths, with a less massive jawbone and jaw muscles. But most fossils of early Homo didn’t even preserve that much evidence: We might have a single piece of a jaw, a part of a skull, or a handful of teeth. Looking at such a fragment, it is natural to assume it belongs to a human or australopith skeleton as we know them. A fragment of Homo-like jawbone would have belonged to a Homo-like body, with a Homo-like brain size. For some scientists, a jaw that looked like Homo should be evidence that the ancient individual belonged to Homo, whatever the rest of the body might say.

With the Malapa skeletons we had vastly more evidence from across much of the body, and yet we found that different pieces of evidence conflicted with the idea that any one part could predict sediba’s relationships. What if we had only found a part of the jawbone? What if we had found only part of the pelvis? Both these parts were more like Homo than other parts of the skeleton, like the legs, feet, or shoulders. If we had only a fragment, our conclusion could hardly help but be different from what the whole skeletons told us.

Because we weren’t sure, we felt it was important to be cautious claiming anything about sediba’s place in our evolution. We would need a lot more fossil evidence to test such ideas. Our team launched into the work of understanding how the different parts of sediba worked, and how they might fit together into a story about how this species had evolved.

This first description of the new species, which made the cover of Science magazine, was just the beginning of our work. Over the next several years, two special editions of Science magazine dedicated to sediba, each with a cover image of Malapa fossils, would appear. In 2011, our team published papers describing in detail the form of the brain, hand, foot, and pelvis. We also were able to refine the date of the fossils, placing them at a very precise 1.977 million years ago. The two skeletons had been sandwiched between two layers of white flowstone, and we discovered that these, in fact, represented the same short span of time that groundwater was depositing the calcite in the cave. By coincidence, a reversal of Earth’s magnetic poles had occurred during the thousand years or so that these flowstones had been forming. This magnetic event allowed our geochronologists to narrow the time between those flowstones to a very small window. Our next series of scientific papers, published in 2013, described more of the upper limb, spine, and mandible, and something about how sediba must have walked with its humanlike pelvis and strange heel.

Luckily, we were able to satisfy the extraordinary amount of interest in and coverage of our science thanks to the fast pace of new research on the Malapa discovery. By this time, almost a hundred scientists were engaged in different aspects of the work on sediba. The team had grown rapidly because the fossils raised so many new questions that required different kinds of expertise to answer. It also grew rapidly because, even before the public announcement of the discovery, I had set the stage for open access to the fossil material. With a significant find of my own, I could create a program of research in any way my colleagues and I saw fit. My instinct was to open the fossils for any scientist to study, and soon dozens had begun to engage in the science, working with our team.

After the sediba publications, other paleo​anthropo​logists sometimes criticized our team for publishing research too quickly. Such criticism may seem hard to take seriously, because we published our first description of the fossils almost two years after Matthew’s first discovery, hardly a sprint. Our team’s open process led to a much wider array of research than a few colleagues and I would have managed by ourselves, and over the next eight years the research led to dozens of publications by our team and other independent scientists. By taking this approach, we have been able to put our conclusions repeatedly to the highest test: open inspection by the field at large. Publishing scientific work is the way that scientists communicate about data. It is the normal way that science advances. That scientific philosophy does differ starkly from a small fraction of paleo​anthropo​logists who work in comparative secrecy for many years on new discoveries, sometimes laboring alone or in small close-knit groups. But in science, we do not accept conclusions because they are faster or slower, whether they take months or decades. We accept conclusions that are supported by data, data that other scientists can see and replicate.

Making the fossils more open to study meant making copies of the fossils available. As early as 2009, I set up a casting program to create replicas of the Malapa remains with just this in mind. We distributed these first casts to colleagues involved in the descriptions, but then to major museums around the world that housed other hominin fossils. The goal was simple: Put a set of casts of sediba in every major museum in the world that had an interest in studying hominin evolution. With the assistance of the South African government, we pretty much accomplished this by 2013.

THE 2011 ANNUAL MEETING of the American Association of Physical Anthropologists (AAPA) took place in Minneapolis. I carried two large, black gun cases to the meeting, packed with casts of every fossil of the two sediba skeletons. I let as many people see the casts as possible, so they could review the scientific findings by looking at replicas of the real fossils instead of simply trusting what we had written. As our scientific colleagues crowded around the open cases, they had to react to what their eyes told them instead of relying upon what they assumed they already knew. It sounds incredible now, more than five years later, to think that this strategy was practically unheard of at the time. I had brought new fossils from Malapa that our team had not yet published, material that only insiders at other fossil sites might ever have the chance to see. It was so unusual, science reporters at the meetings picked up on the story, and wrote not just about the fossil casts and their implications but also about the openness with which I was sharing my finds.

I donated a full set of the Malapa casts to the association, on the condition that it make them available every year. At the 2012 AAPA meeting, we organized a session in which other museums and institutions also provided casts of their fossil hominins. In this case, we included nothing that had not already been published from other fossil sites, but this still included many copies of fossils that were nowhere available for purchase and were not in teaching collections.

The session was a huge success. Scientists and students packed the room, crowding around tables with copies of fossils they had never seen in person. The sediba fossils, along with fossils from other sites around the world, gave rise to intense discussions among specialists who had never been involved in paleoanthropology before. Many of these experts in human biology or anthropology had avoided the study of human evolution because they would not be allowed to see fossil material. One surprise was how popular the table holding the casts of the little Lucy skeleton turned out to be. Even though it had been found nearly 40 years before, many of the anthropologists had only seen it in photos or in museums, and had never been able to examine a copy firsthand. Something in our discipline was shifting, and it seemed as if sediba was the start of it.