Mental obsessions of paleoanthropologists

Robert B. Eckhardt

Maciej Henneberg

 This reply has been written in response to an unrefereed self-promotional piece (Down syndrome theory on Hobbit species doesn’t hold [sic] to scrutiny, by Michael Westaway, Arthur Durband and Mark Collard) that was posted on The Conversation. All of the points, originally raised by these authors in a letter to the editors of Proceedings of the National Academy of Sciences of the United States (PNAS), were refuted by us in our own papers published by that journal.

Because we already have dealt substantively and completely in the published, primary scientific literature, with the criticisms made by Westaway, et al., here we simply will intersperse our responses within the text of this Conversation piece, distinguishing our comments with boldface type.

“Claims that bones found in an Indonesian cave are not the remains of a new species of extinct hominin but more likely modern humans suffering from a chromosomal disorder have been disputed by a new look at the evidence.”

“Last year Prof Maciej Henneberg, of the University of Adelaide, and his colleagues sparked intense debate among human evolution researchers when they published a pair of papers (here and here) in the Proceedings of the National Academy of Sciences.”

“Henneberg and colleagues argued that the so-called Hobbits – known by their scientific name Homo floresiensis – were not a new species of early hominin but just small-bodied modern humans with Down syndrome.”

The statements made in the immediately preceding paragraph simply are not true. They are misleading in several important senses. First, what has been presented in this round of The Conversation is not a new look at the evidence – and most certainly, there is no new evidence; there has not been any more skeletal evidence for more than a decade, despite research funds being spent in the unproductive quest for more skeletons that duplicate the morphological characteristics of LB1. Instead, what Westaway and colleagues have given us here is yet another repetition of the same statements that have been made many times before by the small group of paleoanthropologists who are fixated on reifying the invention of an invalid human species on the basis of wholly inadequate and erroneously reported data. This sort of approach — which involves, as here, “publishing” in a public forum the same, tired old points that already have been refuted in a major international generalist scientific journal — is most unusual in real science.

In our experience, in a vigorous but genuine scientific controversy a dialogue develops. Data are gathered, and logical arguments are advanced, based on a body of evidence that, in the usual case, increases with new investigations. In that context, when a particular statement has been proved wrong it no longer is accorded any weight, and the discussion can move toward resolution based on other evidence (and readers of The Conversation should note that we have presented many points – concerning limb proportions, pelvic anatomy, etc., etc. — that have not ever been addressed by supporters of the supposed new species). There has been no new skeletal evidence of “Homo floresiensis” discovered in Liang Bua Cave or any other site, while genuinely new evidence against the existence of this suspect taxon has been discovered elsewhere (e.g. Palau) and published on definitively by scientists (e.g. Dr. Bonita De Klerk, in a most thorough doctoral dissertation) who are not members of our research group.

Second, and much more important in the context of what should be honest scientific controversy, is the repetition of erroneous statements alleging that we have said that the Flores skeletal remains are those of “modern humans suffering from a chromosomal disorder” as written here by Westaway and colleagues. The misleading pluralization is important in this context. In the two papers that we published in Proceedings of the National Academy of Sciences (PNAS) on August 4, 2014, we went to considerable effort to make it clear that among the supposedly 15 separate “individuals” excavated from Liang Bua Cave there is evidence that, as far as we can tell, only one of them (LB1) is abnormal. The remains of the others simply are far too incomplete for us to be able at this time to make any reliable inferences from them about whether they show a chromosomal-based disorder, or indeed a disorder of any sort. It is possible that some of them might exhibit abnormalities, but that is not part of the inferences that we have drawn. Nor, as our papers document, would abnormalities in more than one specimen be damaging to our interpretation.

Third, the first of our two recent papers in PNAS makes it clear that our point about the non-existence of “Homo floresiensis” does not follow from a particular diagnosis of Down syndrome (however original and strong that diagnosis still appears). Rather, our deeply held skepticism about the tenability of any “new hominin species” being represented in Liang Bua Cave is based on the fact that the totality of evidence provided is so very slight (about 125 to 130 bones in all), and is so largely attributed to just one specimen (LB1) that appears pervasively abnormal regardless of the diagnosis. We repeat here, in addition, that the remains of LB1 have been misrepresented consistently in terms of its stature and endocranial volume, both of which have been exaggerated downward, whether by intention to mislead or by scientific incompetence in estimation. These are not mutually exclusive possibilities, as erroneous observations can stimulate fanciful interpretations. Overlooking the importance of the primary focus of the problem (body and brain size) and focusing on a minor point of anatomy (the chin) that is tangential at best to our analysis and the problem in general, should be seen as diversionary – not as an attempt to resolve a problem, but rather to perpetuate an illusion.

“It’s now more than ten years since a joint Indonesian-Australian team led by the late Prof Michael Morwood announced the discovery of the famous Hobbit fossils from the site of Liang Bua on the island of Flores, Indonesia.”

“Opinions about the significance of the fossils for our understanding of human evolution are generally accepted by the majority of the scientific community, although some researchers argue that the Hobbits are pathological modern humans.”

“But the Down syndrome argument does not hold on the basis of the evidence from the two lower jaws (mandibles) from the site, which belong to individuals known as LB1 and LB6, as we argue in a reply published this month, also in the Proceedings of the National Academy of Sciences USA.”

“Here we summarise the main points we make in our reply.”

“No support for a key claim”

“The LB1 and LB6 mandibles are crucial to Henneberg and colleagues’ argument. Both specimens have a “negative chin,” which is where the outer surface of the bone at the front of the mandible, below the incisors, recedes.”

“INSERT” [see Figure in original]

The statement above that “the LB1 and LB6 mandibles are crucial to Henneberg and colleagues’ argument” is patently false. Here is what we actually wrote in the second of our papers (Henneberg, et al., 2014) in PNAS (small type below comprises verbatim supplementary online material):

Microgenia (Micrognathia). LB1 formally exhibits microgenia or micrognathia, an unusually small chin. However, this feature needs to be considered in the context that there exist at least three alternative explanations for the appearance of microgenia in this specimen: (i) as one of the supposedly primitive features of a totally new human species (1); (ii) as a regional feature common in Australomelanesian populations (10); and (iii) as a developmental consequence of DS affecting the morphology of LB1 (55). The second alternative has been confirmed objectively as true (56), and hence casts extreme doubt on the first alternative as, at best, an unnecessary speculation. Plainly, the normal mandibular phenotypes observable in Australomelanesian populations (Flores, Palau, and elsewhere) are known entities, whereas advocacy of the same features as unique to a hypothetical new species is not only objectively falseas with a great many of the unique features of LB1, they are variable in expression and frequency, thus at best unusual only individually or in combinationbut also is the ultimate philosophical resort to an unknown entity. Just as clearly, the second and third alternatives are not mutually exclusive. The mandibles of LB1 and LB6, often said to be identical, quite evidently are not, by simple visual inspection (shown in figures 14 in ref. 57). This contrast is most readily apparent in ramus height, which is much shorter in LB6; in addition, the symphyseal region in LB6 is flatter and more nearly inclined toward the vertical than the more bulbous and receding anterior contour of LB1.

Pertaining to the second alternative, a mandible with a reduced bony chin is a regional characteristic found widely in normal members of Australomelanesian populations (10, 56, 58), a point that is ignored or denied consistently by advocates of the new species hypothesis; the extreme form of this misrepresentation is in figure 19 and its legend in ref. 57, which purports to disprove our documentation of the existence of a reduced (neutral or negative) chin in some Australomelanesians (frequencies of which obviously vary from population to population in the region) by showing a lateral radiograph on one unidentified Australomelanesian with a projecting bony mental tuberosity supposedly within a facial phenotype that has the appearance of a receding chin given by external soft tissue.The argument fails logically, because other than in a typological framework, any one specimen cannot disprove by proxy the existence of traits found in individuals among multiple populations in an entire geographic region. Moreover, there is reason to be skeptical of this particular example because the soft tissue profile is so tenuous that Brown and Maeda needed to delineate its contours with a line that is drawn in, obscuring if not altering the appearance of the soft tissue itself. Even if we do not reject the augmented evidence provided by this single unidentified specimen, it is obvious logically that the existence of any individual Australomelanesian with some bony chin projection covered by soft tissue that gives it a receding appearance cannot establish the generality of that hypothetical or actual anatomical conformation. Among 76 adult Rampasasa, 93.4% exhibited neutral or negative chins externally, on the basis of their soft tissue configuration. In the entire sample, only eight subjects (15.35%) showed a positive bony chin that appeared neutral on the basis of its soft tissue covering, and no subject exhibited a negative soft tissue chin that concealed a salient underlying bony chin (56).

Independently supporting the observation that results showing that reduced or absent bony chins among the Rampasasa (56) do not stand in isolation are the mandibles recovered on Palau (58, 59). Two mandibular fragments (B:OR-14:8-122 and B:OR-14:8- 771) are from recent adult modern humans (59). As noted by the authors of the Palau study, the former specimen lacks a vertical keel, distended inferior margin, T-shaped keel, T-shaped mental trigone, and associated mental fossae. The less complete second specimen lacks part of the symphyseal region but nonetheless also exhibits a highly reduced mental eminence.

With respect to the third alternative for a reduced chin structure, as shown in Table 1, microgenia is a feature that forms part of the facies commonly seen in individuals with DS regardless of the regional population from which they are derived. It should be noted, however, that although some ethnic(i.e., populational or regional) variations are known (60, 61), the facial morphology of DS shows some constant features (6267), as is true also for other serious developmental disorders such as cleft lip and palate (61). In general, the extensive biomedical literature on abnormal variation presents an entirely different perspective from the typological view widely accepted in paleoanthropology. This point is important because, although perspectives may vary, there is no rational basis for believing anything other than that there is only one set of evolutionary developmental principles that apply to hominin populations past and present. Because there is no extensive biomedical literature on the occurrence of DS in Australomelanesian populations, and also recognizing that the differences of the LB1 mandible from that of LB6 combine a further degree of symphyseal reduction with greater evidence for tooth loss and periodontal disease, in this regard, the LB1 mandible seems broadly consistent with a diagnosis of DS.

Summarizing the above material briefly, the statement by Westaway and colleagues that “The LB1 and LB6 mandibles are crucial to Henneberg and colleagues’ argument” simply is false. Whether these paleoanthropologists did not read the pertinent part of our paper (quoted in full above), or did read it and but could not understand it, or read it and chose deliberately to misrepresent it, is beyond our ability to discriminate. It is up to Westaway, Durband and Collard to tell readers of The Conversation which of these unattractive alternatives they wish to claim as an explanation for their misleading statements.

“The researchers who first described the Hobbit fossils argued that this trait sets the LB1 and LB6 mandibles apart from modern humans, who have a protruding chin, and aligns them with the early hominins, who have negative chins (as shown in the image below of the African Homo ergaster fossil OH 22 below).”

“The mandible of Olduvai Hominid 22 (OH 22) illustrates the archaic nature of the negative chin. Professor Colin Groves, Author provided”

[See original for figure]

The figure of the Olduvai Hominid 22 mandible provided by Westway and colleagues is interesting but irrelevant. It would be pertinent to disproving our thesis about the abnormality of LB1 only if we somehow were insisting that neutral or negative chins did not occur in previous hominin populations. But it is a widely known fact, even to undergraduate students as well as, presumably to Westaway, Durban, and Collard, that they did.  The real question is whether neutral or negative chins occur only in ancient hominin populations and not in any members of recent ones. But of course they do occur in some individual members of regional extant Homo sapiens populations, as we already have demonstrated.

“Henneberg and colleagues reject this claim. They contend that negative chins are often found among the indigenous people of Australia and Melanesia. Consequently, they suggest, the occurrence of negative chins on LB1 and LB6 does not stop them from being modern humans.”

“Henneberg and colleagues offer three pieces of evidence in support of their assertion that negative chins are commonplace among the indigenous people of Australia and Melanesia: two previous studies and a photograph (see figure S3 in the Supporting Information) of a mandible from an Australian archaeological site called Roonka.”

“Unfortunately, none of these pieces of evidence withstands scrutiny. One of the studies has not been published, which means that it has not been peer-reviewed and therefore does not meet the minimum standard of scientific quality.”

“The other study has been published in a respectable peer-reviewed scientific journal but has since been severely criticised.”

“And the Roonka mandible does not have a negative chin. This can be seen clearly in the figure (below), which compares a CT scan of the LB1 mandible with a CT scan of the Roonka mandible.”

“The mandible of LB1 (in blue) compared to that of an indigenous person from the archaeological site of Roonka, Australia. CT scan of LB1 courtesy Prof Mike Morwood; CT scan of Roonka 45 generated by Assoc Prof Arthur Durband, Author provided”

“Thus, there is no reason to believe that Australo-Melanesians often have negative chins and therefore no reason to overturn the assessment that the negative chins in LB1 and LB6 precludes their attribution to Homo sapiens.”

Westaway, Durband and Collard repeat here arguments that already have been dealt with in our response to the same points that they raised previously in their letter to PNAS. Briefly:

  1. The evidence that Westaway, et al. reject as not having been peer-reviewed is:

Hastuti J, Rahmawati NT, Suriyanto RA, Jacob T (2007) The chin in Rampasasa pygmies, West Flores. International Seminar on Southease Asian Paleontology Program Guidebook (Gadjah Mada University Univ, Yogyakarta, Indonesia), p.54.

The above paper was cited as reference 56 in the supplementary online material in our paper (Henneberg, et al. August 4, 2014 PNAS).

The original paper was presented at a major international conference to an audience of several hundred academic specialists. No one in that audience, including Mike Morwood (who was present at the conference) and many other “Homo floresiensis” advocates, raised any questions about the evidence. All of the slides from the paper by Hastuti, et al., were reproduced in the set of DVDs that were distributed to all conference participants. If Drs. Westaway, Durband and Collard were interested in perusing the actual data rather than disparaging evidence that they seem not to have examined, it would not have been difficult. We now have made all of the slides from the presentation available on our website (www.LiangBuaCave.org). There no longer is any excuse for their repeated denial of the obvious.

Incidentally, note the piece by Westaway, et al. in this most recent round in The Conversation, “…has not been peer-reviewed and therefore does not meet the minimum standard of scientific quality” — to use their own words. Of course, this is a double standard: Westaway and colleagues imply that peer review is critical as a test of scientific quality – except for their own expressions of opinion, which of course must be unquestioned wherever they are offered, for example here on The Conversation, regardless of its general audience.

Our own perspective is somewhat different. We believe that in scientific discourse, content is more important than form, which is why we ourselves are bothering to respond in this nonrefereed forum.  But that does not prevent us from observing that it is the contents of the communications by Drs. Westaway, Durband, and Collard that are deficient, whether posted as a letter to PNAS or, redundantly here, after disproof there. The simple fact of the matter is that Westaway, et al. sent a letter to PNAS challenging our findings. We were requested by that journal to respond to their letter, and did so. In our reply we showed that their criticisms were unfounded and distorted. The repetition here does not improve their accuracy.

  1. “The other study has been published in a respectable peer-reviewed scientific journal but has since been severely criticised.” The paper referred to here is:

Berger LR, Churchill SE, De Klerk B, Quinn RL (2008) Small-bodied humans from Palau, Micronesia. PLoS ONE 3(3):e1780.

Severely criticized? Really? Oh, my heavens. Just imagine, severe criticism in science. How novel, how utterly devastating.

Anyone familiar with how science works will realize that criticism is part of the process by which data and theories are evaluated. Ideally scientific criticisms are substantive in nature and accurate in their expression, but as in the case of the piece here by Westaway, Durband, and Collard, in paleoanthropology such conventions are not always observed. Those familiar with the field of human evolution will know that, to choose another example, Raymond Dart’s 1924 description and diagnosis of the Taung skull as the first australopithecine was “severely criticised” – really severely criticized, for decades — and Taung was not accepted generally as a hominid until the mid-1950s, and then chiefly because the fraudulent Piltdown find was removed as a valid specimen. Nonetheless, severe criticism is not the same as presentation of appropriate scientific disproof. Piltdown, “Eoanthropus dawsoni,” was defended widely for decades; in the case of “Homo floresiensis” we are just into the early years of our second decade of attempted defense of the indefensible by its partisans, in the face of growing contrary findings. The Palau skeletons described by Berger, et al., however criticised, constitute regional evidence that is highly pertinent to discussions of the Liang Bua Cave remains.

“More inconsistent data”

“The chin is not the only feature of the LB1 and LB6 mandibles that does not support Henneberg and colleagues’ argument.”

“A study that was published several years ago identified a number of other traits that LB1 and LB6 share with early hominins but not with modern humans.”

“One of these traits can be seen in both the photograph of the OH 22 mandible and the CT scan of the LB1 mandible. On the inside of the front of the mandible there is a bulge. Such “buttresses” are common in early hominin mandibles but are not found in modern human jaws.”

The statement above, as with many others made by Westaway, et al., is incorrect. Whatever the morphology of the OH22 mandible dated to very roughly a million years ago and found on another continent, Africa, unless evidence is provided to connect its population with that represented by the Liang Bua Cave remains, the specimen is irrelevant to observations on mandibles of recent humans, which is the point at issue here. The anterior symphyseal portion of the mandible is highly variable in normal human mandibles from the region that includes Palau and Flores. See Figure 5 and its caption from Berger, et al. (2008).   

“A second trait that distinguishes the LB1 and LB6 mandibles from those of modern humans is the presence of [a] distinct gap between the end of the tooth row and the rear section of the jaw.”

This statement is untrue and ignores evidence that already has been presented in the response that we made in PNAS:

Noerwidi S (2012) The significance of the Holocene human skeleton Song Keplek 5 in the history of human colonization of Java: a comprehensive morphological and morphometric study. M.A. Thesis, Erasmus Mundus (Muséum national d’Histoire naturelle).

As indicated in the title of the reference, Song Keplek 5 is a Holocene human mandible that exhibits a retromolar sulcus. Other examples of retromolar sulci could be cited from elsewhere in the world.

 It is difficult to decide which is more indicative of scientific malpractice on the part of Westaway, Durban and Collard: initially being unaware of evidence from the region pertinent to Flores that refuted their statement before it was published in error; or their choosing afterward, as here, to pretend that this evidence contrary to their position does not exist.

“A third trait that links LB1 and LB6 with the early hominins rather than modern humans is the form of their tooth roots.”

More than a decade ago I published a paper that established clearly the point that numbers of tooth roots occur polymorphically in human populations distributed over time and space:

Eckhardt RB (2003) Polymorphisms past and present.  Human Biology 75(4):559-575.

Once again, Westaway, et al. choose to ignore data that contradict factually a position that is counter to the one that they would prefer to be the case.  

“Henneberg and colleagues ignored these traits, but their presence in LB1 and LB6 provides strong support for the hypothesis that the Liang Bua fossils are the remains of early hominins and not those of modern humans.”

As noted in our response published in PNAS and noted again here, we did not ignore these traits, but showed – with evidence – that Westaway and colleagues simply were wrong.

It should be added that the “remains of early hominins” from Flores to which they refer all are dated – however questionably – to a time within the last few tens of thousands of years during which only members of our own species are known everywhere else in the world. The Flores skeletons are not “early hominins” somehow inexplicably caught in a time warp, but instead contemporaries of other Homo sapiens populations and exhibiting features – normal and abnormal – known to be found in other members of our species.

“Taking it on the chin”

“The Down syndrome hypothesis is the latest in a long line of attempts to explain the features of the Liang Bua hominin fossils as pathologies.”

Here again, Westaway, Durband, and Collard continue their misrepresentation of our position. We have not presented data establishing  that ALL the Liang Bua hominin fossils” – note the plural again used here by Westaway and colleagues, as well as the misleading designation as fossils specimens that are not — are pathological. Instead we have made a strong case that the most complete specimen, LB1 (which in and of itself comprises the great bulk of the skeletal elements from the cave), manifests developmental abnormality. The remaining few bones from the cave representing other skeletons are inadequate to allow reasonable certainty on the point of whether the individuals that they represent were normal or abnormal, and at this point there is no need to posit abnormality for all of them.

The LB1 specimen clearly is abnormal, however, and this point cannot be avoided by other than wishful thinking based on misconstrued data.

“It should be the last, we think.

The mandibular evidence disproves the idea that LB1 and LB6 are modern humans, and there are a number of other lines of evidence that do so too, as the work of Prof William Jungers, Prof Peter Brown, and several other colleagues has demonstrated.

It is time for the field to move on. The Hobbits are a new species of early hominins not modern humans with Down syndrome or indeed any other pathological condition.”

It is difficult to conceive of a more self-servingly unscientific statement than the one immediately above, that “It is time for the field to move on.” This statement is particularly out of keeping with the best traditions of science, even a scientific field as commonly partisan and insular as paleoanthropology.

Raymond Dart published his brilliant and prescient description and diagnosis of the Taung child’s skull in 1924, and was attacked widely and savagely for his effort. But neither he, nor even his critics, who turned out to be wrong for all sorts of reasons, called for an end to the quest for pertinent evidence. Indeed, one of the most intellectually and empirically heroic – and I use that term, “heroic,” with full cognizance of its meaning — chapters in evolutionary biology is represented by the work of Dart, Broom, Schepers, and Robinson. This small group of outnumbered and underfunded researchers worked through the 1920s, 1930s, 1940s, and early 1950s to recover steadily more and more abundant and diagnostic australopithecine remains from a variety of sites. MH knows well about this quest, having been a successor to Raymond Dart in his Chair at the University of Witwatersrand in South Africa. Being outnumbered and underfunded does not equate with being wrong. Science is not a democracy but rather a meritocracy, one in which superiority of evidence and reasoning in the long run trumps popularity in the short run.

Where is the spirit of Dart and his colleagues in the debate over the sparse and fragmentary human skeletal remains from Liang Bua Cave? Reiterated rhetorical misrepresentation of our work will not serve. Nor will a continued pattern of garnering research funds for archaeological work that produces no tangible results. Science deserves better than this farrago.

Robert B. Eckhardt

Maciej Henneberg

15 March 2015

 

 

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