Paleoanthropologists reconstruct human history from scant and enigmatic traces of a distant past—often from little more than a handful of objects. The human fossils that form the basis for the discipline are hard to find and not much easier to study. In a highly competitive environment where research material, economic resources, and intellectual property rights are at stake, new discoveries are, at times, closely guarded by their finders. Competition both drives and constrains research as, perhaps inevitably, personal interests become intertwined with questions about our heritage. In recent years, the development of powerful tools for digitization and analysis have provided paleoanthropologists with new ways to preserve and circulate fossil data. For all these reasons, it is time to reconsider our current vision for paleoanthropological research and propose better procedures. The objective should be to maintain proper attribution for new discoveries while ensuring the widest possible dissemination of knowledge.
Origins
One of paleoanthropology’s most striking characteristics is its relatively brief history as a scientific discipline. It was only in the late nineteenth century that researchers began collecting human fossil specimens in a systematic manner. When human remains were unearthed in prior eras, they were treated as curiosities rather than being subjected to rigorous scientific analysis for the purposes of understanding human variability and evolution. Throughout paleoanthropology’s short history, each era has brought new challenges. During the field’s development, paleoanthropologists first had to integrate the theory of evolution, then to accept the notion that other species of humans had existed, and, finally, to embrace the uniqueness of present humanity.
Another important aspect of the field is the interpretational difficulties it poses for researchers. Analyzing fragmentary evidence from long-distant epochs is a process fraught with ambiguity and uncertainty. Research involving human fossils also has obvious implications for our understanding of who we are. In turn, this lends human fossils, already extraordinary in their own right, an additional symbolic value as distant milestones in our own development. Yet, from a strictly paleontological point of view, this is not really the case—ancestrality is rarely straightforward. The human fossil record nonetheless has a particular significance that distinguishes it from the vestiges of any other ancient lifeform. The skeleton of a Tyrannosaurus rex may be worth a great deal of money, but it has none of the symbolic weight imbued in even the tiniest fragments of an ancient human species.
When the name Homo sapiens was introduced by Carl Linnaeus in the mid-eighteenth century, more than 100 years before the field of paleoanthropology emerged, its significance was not merely as an exercise in binomial nomenclature—it was a challenge to the deep-rooted assumption that humanity and the rest of the zoological realm should be understood separately. The discoveries that took place during paleoanthropology’s development were important events, both for the field and broader society. As a result, the identification of a new human species was often a complicated and drawn-out process. First proposed in 1863, the notion of Homo neanderthalensis as a distinct species of archaic humans was only embraced at the beginning of the twentieth century after numerous additional specimens had been found. Similarly, Homo erectus and Australopithecus africanus were not widely accepted in the field for several decades after being described in 1894 and 1925, respectively. Even in the last 30 years, the identification of the oldest known hominids—Ardipithecus ramidus, Sahelanthropus tchadensis, and Orrorin tugenensis—has been the subject of vigorous debate among paleoanthropologists. The same is also true for the identification of Homo floresiensis and, more recently, Homo naledi.
Accessibility
Some of these disputes can be attributed to structural issues within the field. A paleontologist seeking either to be convinced by the claims of a fossil’s discoverers, or to convincingly refute them, would need to study the holotypes for each of the aforementioned species.1 This is not a realistic prospect due to the way the field operates. Fossils are scattered across collections throughout the world, with varying levels of accessibility, whether due to tensions between laboratories and researchers, geopolitical conditions, or simply the travel costs involved. The most recently excavated fossils are unavailable to the wider field because their discoverers understandably wish to be the first to describe and analyze them. There are no consistent rules governing access to fossils, nor is there any likelihood that such a scheme could ever be formulated or enforced. Solutions to the problem of access must be found using other means.
Finding fossils is hard and time-consuming work. Analyzing new discoveries often requires similar levels of concentrated effort. Consider the case of “Little Foot,” a near-complete 3.67 million-year-old Australopithecus skeleton discovered at Sterkfontein in South Africa.2 Two decades elapsed between the initial discovery and its public unveiling in 2017, primarily due to the difficulties involved in extricating the fossils from the surrounding rock. Admittedly, this is an extreme case, but it serves to demonstrate that the timeline between discovery and publication can be unpredictable. Between these milestones, the wider field is left to ponder the implications of what might eventually be revealed. As is the case with the problem of accessibility, there are no obvious administrative solutions. Time limits cannot be imposed for the preparation and analysis of a new discovery.
It seems clear that a short notice, detailed description, and initial publication soon after a new discovery is made would represent a step forward. A few researchers have already adopted this approach, but it should be common practice. These data could be used to begin assessing the validity of the findings and to situate the new specimen within the narrative of human evolution. Practices for presenting new results vary considerably between scientific disciplines. Mathematicians and physicists circulate preprints via repositories such as arXiv so that other researchers can test and challenge their findings before they are published in journals. A similar service, bioRxiv, has been established for the biological sciences. Geneticists, including paleogeneticists, add new sequences to a database, albeit without initially releasing their full analysis. Paleoanthropology could benefit from embracing some of these methods for disseminating new ideas and discoveries.
Imaging
The first and last occurrences of a species in the fossil record are more difficult to establish in paleoanthropology than in paleontology. Because so few human fossils have been found, when new specimens are identified, the timeline of human development can shift drastically as a result. For decades, the oldest fossils attributed to Homo sapiens were the remains found between 1967 and 1974 at the Omo Kibish site in Ethiopia and dated to 195,000 years ago. The oldest found outside Africa were those unearthed at Qafzeh in Israel and dated to 90,000 years ago. In 2017, specimens found at the Jebel Irhoud site in Morocco were re-dated to roughly 280,000 to 350,000 years ago.3 The following year, a fossil from the Misliya site in Israel was dated to between 177,000 and 194,000 years ago.4
These results indicate that our species is much older, and left Africa much earlier, than we had previously thought. It is important to note that we are yet to find any other fossils in these locations dating from the period between 300,000 and 100,000 years ago. We are thus none the wiser as to precisely where our species originated or when it first left Africa. There are simply insufficient data to extrapolate further. Indeed, similar limitations apply for many theories. But the old adage that any new discovery in paleoanthropology is sufficient to upend the theories in place is, at best, an exaggeration. Exceptional discoveries do occur from time to time—Homo floresiensis is a good example.5 But most only upend assumptions that were based on too little data.
The discoveries that do challenge established theories are often poorly received. This would likely be improved if the quantitative data used in studies were more widely available. Few papers in paleoanthropology, whether published in Nature or elsewhere, include the raw data that support their findings. Any publication should include, wherever possible, full measurement details, especially for fossil samples with limited accessibility and for new fossil specimens. Details in relation to cranial thickness, tissue volumes of teeth, sinus size, semicircular canal dimensions, and the like must be documented.
Gathering these details can be an issue when the specimens are as fragile, rare, and valuable as those in paleoanthropology. The models generated from X-ray-based imaging techniques offer solutions to these problems as well as, potentially, a means to improve the accessibility of fossil data. High-resolution three-dimensional models describe an object’s shape and surface characteristics, as well as its internal composition, at a level of detail suitable for researchers.6 The internal structure of specimens can be scanned without affecting either their integrity or prospects for preservation. Geometric morphometrics offer new options for analysis based on a set of coordinates that describe morphologically distinct features among a set of specimens. From these coordinates, methods of statistical analysis are used to identify variations in form.7
These new approaches are not without their limitations. To date, there have been no large-scale studies examining the effects of the intense and often repeated exposure of paleoanthropological specimens to X-rays.8 In some cases, these imaging techniques have been found to have implications for other types of analysis. A study found that CT (computed tomography) scans of teeth involved radiation exposure sufficient to leave traces in the enamel, rendering ESR (electron spin resonance) dating ineffective.9 For microtomographic analysis, the level of irradiation, it should be noted, has been found to have little or no impact on the preservation of ancient DNA.10 Technical standards for fossil imaging should be defined to help guide researchers in their use of these techniques.
Another limitation involves the conservation and sharing of data. The question of ownership, not to mention the management of data, is far from straightforward in some countries. Ideally, custodian institutions would be responsible for generating the raw digital data for the objects in their collections. In France, imagery obtained for scientific research is free of copyright since it is an objective replica of a specimen, without any artistic or personal contribution. All the tomographic data generated from the anthropological collections of the Muséum national d’histoire naturelle in Paris are available for any scientific project.11
Homo naledi
Long-held paleoanthropological conventions were turned on their head following the discovery of Homo naledi in South Africa in 2013. This was a significant discovery for numerous reasons, chief among them being the age of the fossils. The specimens are relatively recent, dating from around 300,000 years ago, yet they possess anatomical characteristics reminiscent of the very first members of the genus Homo—the skull of naledi has similarities to that of habilis, which lived two million years ago. The identification of a species with such ancient features that lived almost at the same time as Homo sapiens and Neanderthals was a stunning development.
The discovery of Homo naledi was also notable for the quantity of specimens recovered. More than 1,500 bones were collected during excavation campaigns in 2013 and 2014. The very first scientific articles describing the species were published just a year later, in September 2015.12 Never before had the details of a new human species been published so quickly. The decision to publish at this time was, in fact, both bold and highly unusual. Excavations were still ongoing and the first articles about Homo naledi did not appear in the major journals where important discoveries were usually announced. A collection of 133 high-resolution three-dimensional scans were also made available online when the first articles were published.13 These included scans of the most complete bones, in particular all the specimens used as holotypes or paratypes to define the species. All of this flew in the face of established practice. To date, no other fossil series has ever been made available, even virtually, at the time of first publication.
Since the first papers announcing the discovery were published, there have been numerous studies that have fleshed out the initial descriptions. Still, the novel approaches and speed with which Homo naledi was presented to the field proved polarizing. The way the discovery was handled has been the subject of much debate and generated considerable criticism. Judging from earlier discoveries, this mixed reception should come as no surprise. Such a significant announcement will also inevitably overshadow other specimens and hypotheses, particularly when accompanied by widespread media coverage.
In contrast to the Homo naledi specimens, the fossils of other species that might form the basis for worthwhile comparisons, are accessible only to varying degrees and in some cases not at all. An exhaustive comparative study would be impossible for the simple reason that access to the material from other important discoveries is often limited to just a few tens of specimens. It is for this reason that the release of the high-resolution Homo naledi scans is an event, in my view, almost as striking as the announcement of the new species and represents a significant milestone in the development of the field.
Translated and adapted from the French by the editors.
