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paleoanthropology, genetics and evolution

Photo Credit: Remains of Homo naledi. John Hawks CC-BY-NC-ND

How long does it take to publish new hominin species after discovery?

In an earlier post, I looked at descriptions of new hominin species during the last 25 years, to see how long they took from submission to acceptance in the journal where each was published (“Hominin species and time in peer review”). The data show that these papers have taken a median time of 70 days to review. But as I noted, the time in peer review probably doesn’t tell us very much about the quality of review. What stands out is that the duration of review has not changed appreciably across the 25-year span.

Au. sediba
Australopithecus sediba was 20 months from first discovery to publication. Photo credit: Lee Berger

A more interesting time interval is from discovery to publication. This time includes not only the peer review and other editorial processes, but also the primary scientific work. Technicians prepare and conserve the fossils, specialists in anatomy take systematic measurements and observations, and they carry out comparisons with other samples of fossils and skeletal collections.

Analysis can take a lot of time. Some fossils require considerable reconstruction. Today such reconstruction can be carried out virtually after 3D scanning of the material, which sounds like it should save time but somehow always seems to take longer. If a specimen preserves a rare piece of anatomy, the comparable anatomical areas may not have been well-reported in other fossil samples, and therefore one or more researchers may need to make special research trips to study fossils from other parts of the world.

Considering the diversity of fossil preservation across different field sites, you might expect the process of publishing diagnoses of new fossil species to be equally diverse in how long they take to prepare.

The data show the opposite: the duration of scientific work preceding the diagnosis of new hominin taxa has generally been between one and two years, and has remained pretty much the same over the last 25 years.

Discovery dates

When was a species found? This is not a simple question, because the evidence for a new species is rarely limited to a single specimen. A team may find fragments that suggest the existence of a new species in one field season, and later find additional evidence that enhances the case.

For example, the earliest specimen now attributed to Australopithecus anamensis to have been discovered is a humerus fragment from Kanapoi, KNM-KP 271, which was found by Bryan Patterson’s research team in 1966. This fragment was known to represent a very early hominin, but does not present anatomical features that would have enabled a clear diagnosis relative to other known hominin species. Only much later did Maeve Leakey and colleagues uncover more remains from Kanapoi and Allia Bay that enabled a diagnostic comparison with other species.

Every formal description of a new species designates a single specimen, known as the “holotype”, that will serve as an anatomical reference for future scholars. Under the rules of the International Code of Zoological Nomenclature, the holotype is forever tied to the formal species name; it can never be recycled to serve as the holotype for any other species name. For Au. anamensis, Leakey and colleagues designated the specimen KNM-KP 29281, discovered in 1994, as the holotype of the species. So although the first specimen now attributed to Au. anamensis was found in 1966, the holotype was found 28 years later.

Even the holotype discovery date is not really the time of “species discovery”. Generally, a team of scientists tests the hypothesis that a new fossil assemblage belongs to an existing species. If the evidence rejects this hypothesis, a team may move toward formally defining a new species. “Discovery” of this new species may happen more-or-less gradually during the analysis of fossil remains, as researchers develop evidence in comparison with other fossil samples. In some cases the team may recognize this distinctiveness very rapidly, in others more slowly, depending upon the quality of the evidence and the difficulty of making the comparisons. Sometimes additional field seasons may be necessary to add more fossil specimens and thereby broaden the scope of comparisons. In some cases, it is the holotype that is unearthed during a later field season, well after a field team has other specimens that make them think a new species exists.

Looking at the records available in formal taxonomic diagnoses, the only practical alternative is to consider the time of holotype discovery. Papers usually report this date and do not reliably list the discovery dates of paratype specimens. Even with holotypes, the reporting is uneven. Some papers have reported a single day of discovery, in which case it is simple to calculate the time from discovery to publication. In many cases, however, only a month of discovery (e.g., “March 2014”) is provided. There several reasons why a single date may not be available. A holotype may have taken several days to uncover during excavation, or it may have been reconstructed from fragments found over a range of dates. In extreme cases, parts of a holotype might have been found in successive field seasons.

In a few cases, the paper gives only the year of discovery (for example, the only date given for KNM-KP 29281 is “1994”). For my comparisons here, if the paper gives no indication of the timing of the field season, I have assigned a date of January 1 to these discoveries. The resulting timeline is necessarily longer than the real time taken by a research team to describe its discovery, in theory up to 12 months longer if the specimen was actually discovered in December.

The results

Number of months from holotype discovery to publication for hominin species since 1990
Asterisks (**) indicate species for which the discovery year was supplied but not the date; the point in this graph assumes discovery on January 1 of that year, making this the maximum possible time from discovery to publication. In reality they may be as much as 12 months less than indicated here.

In this chart, H. cepranensis is an outlier, as discussed below. The remainder of the data show no reduction or increase in the time from discovery to publication over the last 25 years. Out of the fifteen formally named taxa here, ten were published within two years after the discovery of the holotype specimen. Only two of those appeared within one year after discovery. The median time from discovery to description is 20 months.

The x-axis of the chart is the discovery date, not the publication date. There may be taxa that have been discovered in the past few years that have not yet been published, and obviously any such species would not be represented in the chart. H. gautengensis, published in 2010 but based on a holotype discovered in 1976, is not included in the chart.

This period of two years or less includes the time spent by the species in peer review and revision, which I discussed in the previous post. In the case of Homo floresiensis, for example, the time from submission to acceptance of the manuscript was more than 6 months, and the publication of the paper was still only 14 months after the discovery. The paper describing Australopithecus ramidus was slightly more than two months from submission to acceptance; the total timeline from discovery of the holotype to publication was only 9 months.

In light of discussion about the publication pace of Homo naledi, these data may surprise people. H. naledi may be remarkable for the quantity of anatomical evidence, but not the time from discovery to publication. It took substantially longer to move from discovery to publication for H. naledi than for Au. ramidus (9 months), S. tchadensis (12 months), or O. tugenensis (3 months), and even longer than H. floresiensis (14 months) and Au. garhi (17 months).

What explains the consistency in time to publication?

A varied array of research teams around the world have composed effective and highly-cited diagnoses on a varied array of fossil assemblages, with all necessary research and editorial handling and peer review within two years or less. Setting aside diagnoses of new taxa based on previously-published fossil assemblages, the timeline of the procedure has been remarkably consistent.

I think this consistency of timeline can in large part be attributed to the consistency of content.

  • Formal diagnoses follow a common recipe, with a stereotypical block giving essential diagnostic information, and a discussion that places the new taxon into a phylogenetic and adaptive context.

  • The addition of a new taxon generally must reiterate the key information of the next most similar taxon.

  • Most diagnoses of hominin taxa are relatively short, with a median of 7 text pages. Only Homo naledi and Homo gautengensis were diagnosed in papers longer than 11 pages.

  • Although scientific papers have undergone a major trend during the past 15 years to add supplementary information in addition to the main text, this has affected very few of the hominin taxa included here. Only Au. deyiremeda, Au. sediba, and H. floresiensis were accompanied by supplementary information of substantial length.

Some of these species are now represented by fossil samples that were difficult to reconstruct and analyze. But in nearly all cases, the reconstruction and analysis was a second phase of work that followed the formal diagnosis of the new taxon. Therefore most of the difficult work of reconstruction could follow formal diagnosis. This was perhaps most famously the situation with Au. ramidus, where the most famous specimen is not the holotype. But to one degree or another, the process of later, deeper description has been a routine part of the study of most of these species.

The exceptions

What about the exceptions, the species that took much longer than two years to diagnose?

Five taxa required more than two years from discovery to publication. The diagnosis of one of those taxa, H. cepranensis, was based on a holotype specimen that had been described in a peer-reviewed publication several years earlier. To this we can add several similar cases of new formal diagnoses of taxa published in the last 25 years based on previously published fossil material.

  • Curnoe (2010) based the diagnosis of H. gautengensis on StW 53, which was found in 1976, with a description published by Hughes and Tobias (1977).

  • White et al. (1995) based their diagnosis of the genus Ardipithecus on the species diagnosis of Au. ramidus published in 1994.

  • Haile-Selassie et al. (2004) based their diagnosis of the species Ar. kadabba upon the diagnosis of the subspecies Ar. ramidus kadabba that Haile-Selassie had previously published in 2001.

I don’t think these cases are directly comparable to the original first assessment of newly excavated material. Such secondary study is also a process of discovery, sometimes undertaken due to the recovery of additional material (as in the case of Ardipithecus), but the timeline of such research is extremely variable.

Two of the taxa that took longer than two years to diagnose were subspecies: Ar. ramidus kadabba and H. sapiens idaltu. Providing such formal diagnoses of subspecies is a relatively new innovation in hominin taxonomic practice. One motivation to name a subspecies is to preclude the use of a holotype specimen for other taxonomic diagnosis in the future. As the case of Ar. kadabba shows, future discoveries may force a reassessment of the variation presented by a sample, sometimes prompting the promotion of such a subspecies to a species-level taxon.

I can think of two hypotheses to explain why the diagnosis of these subspecies has occupied a longer period of time than species or genera. One possibility is that the relatively subtle anatomical variation that distinguished a subspecies may require more time to fully understand and characterize. A second possibility is that researchers may work on new species and genus-level diagnoses with greater intensity than a subspecies diagnosis. These are not mutually exclusive, and probably there are other possibilities as well. But again, it is not clear that researchers treat the formal diagnosis of a subspecies as the same kind of task as the diagnosis of a higher-level taxon.

This leaves only Au. deyiremeda and H. antecessor, which required approximately 4 years and 3 years from holotype discovery to description, respectively. Both of these are instances in which additional field seasons may have added more information from additional specimens, and as I move forward, I’ll consider whether the sample size and anatomical regions preserved in the holotype and paratype specimens help to explain the timeline of either of these taxa.

Is everyone “rushing” their research?

The standards by which I judge the quality of science are replicability and originality, not speed. The formal diagnosis of a taxon is one of the least creative exercises in paleoanthropology, with several highly standardized parts. These essential ingredients have emerged through history as a way of ensuring the replicability of the key observations that contribute to attributing other fossils in the future. Considering that many hominin fossils are practically inaccessible to independent scientists, scientists must insist that the formal description of such fossils will meet a high standard of replicability.

With that in mind, is there a correlation between replicability and speed of publication?

I don’t think so. Among the papers that are published within four years of holotype discovery, I just don’t see any obvious correlation between time to publication and replicability.

Keep in mind that this is a very small sample to try to find such a correlation. Certainly there are papers here that omit crucial data, there are papers that have given rise to years of controversy, and there are papers that have led to relatively little subsequent reassessment of the broader phylogenetic pattern of hominins. Any set of independent scientists would probably have a wide variety of “favorites” or choices as “best hominin description EVAH”.

But even if we take the strongest critics of new species, I don’t think we see any relationship between a person’s preferences about which diagnoses are replicable and the timeline of publication.

As an example, Tim White has been publicly critical of many of these species as examples of “taxonomic inflation”. Such “inflated” species include H. naledi, Au. deyiremeda, Au. sediba, K. platyops, O. tugenensis, S. tchadensis, Au. anamensis, and H. georgicus. I may be missing several. The median time from discovery to publication of these eight taxa is at most 20 months. The median time for the three taxa published by White himself is 17 months. Whatever the standard of quality and replicability applied by White, time is not an explanation.

Production of a taxonomic assessment for newly discovered hominin fossils is a basic responsibility of field research. Assessing whether a fossil or an assemblage belong to a previously-known taxon is relatively straightforward. That assessment may rely upon small anatomical details, but a review of the anatomy of a fossil will not likely miss those details if they are present. So there’s nothing about the procedure that in principle should take many years to accomplish.

In light of the evidence from the last 25 years of formal taxonomic diagnosis in hominins, it is clear that in most cases, this process is very efficient.


  1. As in the previous post, I am missing data for Australopithecus bahrelghazali.


References for this post are the same as listed in “Hominin species and time in peer review”.