As the title of this book implies, authors Chris Rupe and John Sanford lead us on a journey to illustrate how most of the major hominin fossil discoveries have invariably been the source of much discussion and differing interpretations in the field of paleoanthropology. The “contestation” among leading “paleo-experts” (a friendlier term used throughout the book instead of “paleoanthropologists”) is documented with extensive use of quotes and relevant passages from the primary scientific literature, published historical retrospectives, and science news commentaries.

This systematic review accomplishes two main goals. The first is to show that the linear picture of human evolution from ancestral australopithecines is not clearly corroborated from the perspective of the fossil record. Instead of being able to arrange fossil remains in a nicely defined tree structure, paleo-experts are puzzled by what looks more like a tangled bush. “Leading evolutionary scientists acknowledge there are immense difficulties and inaccuracies in the reconstruction of hominin skeletons […]; immense difficulties in correctly dating hominin sites […]; and still no convincing fossil evidence of the critical bridge species which may connect australopiths to Homo” (p.333). The second goal is to highlight the disconnect between this uncertainty, acknowledged in academic circles, and the popular perception of a definitively set picture of human evolution (essentially looking like the iconic “march of progress” illustration). “Why doesn’t the public hear about all the controversies within paleoanthropology? Introductory-level textbooks and the media have failed to present the controversy to students and the general public. This has created the false impression that paleo-experts are in general agreement with one another regarding all the major claims. […] Our goal is to help people hear both sides of these controversies, so they can make better-informed decisions regarding the important question of where we came from” (p.27).

The book emphasizes the strength of the evolutionary paradigm and its effect on the presentation of data. This point is addressed, for example, in chapter 3, which is a masterful description of the trajectory of “rehabilitation” of Neanderthals, from brutes to fully humans, or in the discussion of an illustration published in the journal Science (chapter 6), showing how subtle tricks of the trade we thought we should not worry about in the 21^st century are still used to push an agenda. The book also offers a historical perspective on some of the social components (the power of “group think” and the quest for prestige) that play a role in the way new findings are interpreted (see, for example, chapter 7, which relates the controversy surrounding the classification of hominin fossil material from Hadar and Laetoli).

Contested Bones is well written, nicely illustrated, with accessible language that accomplishes the difficult task of simplifying what can often be very technical jargon, while capturing the essence of relevant information without losing accuracy. The organization of the book is straightforward. The first two chapters are introductory, and lay down terminology, background, rationale, and objectives of the book. Hominin fossil remains are then reviewed in 3 major sections entitled: 1) Bones of the Human Type; 2) Bones of the Ape Type; and 3) Bones of the “Middle” Type. The final chapters present more explicitly the personal interpretative model of the authors but also include two “diversions” into peripheral but relevant topics: the complexities of dating hominin remains (chapter 12) and a discussion of genetic evidence of significance for the hypothesis of human evolution (chapter 13).

Rupe and Sanford have their own views on how to interpret the fossil record of hominins, and have the merit of communicating them with openness and transparency. An interesting dynamic characterizes this book: on the one hand, the reader instantly perceives the militant passion of the authors and their desire to clearly state their perspective; at the same time, the discussions of the paleo-experts are often left to speak for themselves and the reader immediately grasps that this debate is real, not just the fabrication of two fringe dissidents. This “dual register” will make the book a valuable and engaging read also for those who do not agree with the authors’ interpretations, because they will still find much primary information to stimulate personal reflection and further documentation.

What then is the authors’ model? First of all, Rupe and Sanford identify themselves as “lumpers:” “We do not trust the tendency of splitters to define every variant as a new species. We feel lumpers are more realistic” (p.16). They see the human species as able to express a significant amount of skeletal plasticity, part of which could arise from pathology and genetic degeneration. Starting from this premise, they suggest hominin remains can be assigned to distinct types (one human clade and several ape clades), which coexisted and expressed variability within their own lineages but are not related by an ancestral-descendant relationship (fig. 3, p. 342). Therefore, their model falls well within the traditional creationist understanding of human origins and of the hominin fossil record. Perhaps, what the book adds to this understanding is a stronger emphasis on inbreeding within small isolated populations as a key mechanism for generating skeletal variability. Interestingly, this intuition put forward in the book is currently being discussed in prestigious mainstream publications (pp. 337-340). The book also adopts a strong stance in interpreting much Pliocene hominin fossil material as human, as discussed in chapter 11 (Coexistence – Australopith and Man).

When it comes to the specific taxa discussed in the book, the conclusions of the authors can be summarized as follows: Neanderthals are fully humans; Homo erectus, H. floresiensis, and Homo naledi are degenerative human varieties reflecting isolation and inbreeding in small populations experiencing scarcity of resources; Ardipithecus ramidus is an extinct ape; the collection of bones assigned to Australopithecus afarensis represents in part ape remains but also includes misclassified human remains; Homo abilis is a wastebin taxon established from a collection of both human and ape remains; and Australopithecus sediba is a chimaera obtained from erroneously mixing human and ape bones in the reconstruction of two partial skeletons.

This latter claim was something I had not heard stated so forcefully before. In the original publications describing the two partial skeletons representing the holotype and paratype (MH1 and MH2), Berger, the discoverer of Au. sediba, and his collaborators report: “the two skeletons were found in the same stratigraphic horizon, […] separated from one another by no more than half a meter horizontally. The remains of one individual (MH2) were recovered in partial articulation, while those of the other (MH1) were somewhat more disturbed, yet still in close association (distributed over an area of less than 2 m²).”[1] “Bones of the Au. sediba MH2 right wrist and hand were uncovered in a cluster and in close association with the remainder of the right upper limb.”[2] “Foot and ankle elements recovered from the Malapa site […] include an articulated distal tibia, talus, and calcaneus directly associated with the female paratype skeleton, Malapa Hominin 2 (MH2).”[3] “Both individuals preserve a number of thoracic remains that were found in near articulation.”[4] Contrast this with Rupe and Sanford’s assessment of the evidence: “most of the remains were found as separate parts. Only a few of the bones were found in anatomically credible association. The site consisted of a mixed bone bed of many different types of animals; most of the bones were not found physically connected to one another. Thus it is possible that Sediba is not a legitimate species but may be a mixture of bones from more than one species.” In fairness, there are paleo-experts who have suggested the possibility that a mixture of different species is represented in the Malapa hominin material,[5] and their concerns are discussed in the book. Moreover, none of Berger’s et al. original publications seem to contain a diagram showing the spatial representation of individual fossil fragments positioned where they were encountered during excavation. This basic type of primary data would help to form a better idea on the merit of the mixture hypothesis. How this controversy will be resolved will have a major impact for the book, because the authors specifically distinguish portions of the Au. sediba skeletons they think represent human or ape remains. If each partial skeleton indeed comes from a single individual, there would be no other option but to admit that “mosaic” forms are represented in the hominin fossil record, a conclusion Rupe and Sanford seem to resist. If, on the other hand, there is commingling in the Malapa site partial skeletons, the strong stance of the book would be vindicated, projecting considerable credibility on the broader model advocated in the book.

The chapter on dating focuses on K-Ar, Ar-Ar, U-Th, and U-Pb methods, and includes two examples of age determinations that were controversial or complicated (a tuff bed from Koobi Fora, Kenya, and the Homo naledi remains from South Africa). With a critical outlook, the chapter not only points out the difficulties and examples of documented inaccuracies in dating methods, but casts the shadow of cherry-picking and pre-determined selection of acceptable age ranges to the exclusion of anomalies. In their effort to show that this also is a “contested” area in paleoanthropology, the authors seem to project a lack of confidence in the value of the radiochronological enterprise. However, the question of dating remains tangential to the main thrust of the book, which reviews hominin remains within the current conventional understanding of their stratigraphic placement.

The chapter on genetic evidence and human evolution discusses the problems of generating novel genetic information through selection of random mutations, and contains a rebuttal of evolutionary arguments like the human chromosome 2 fusion model. Particularly powerful and instructive was the review of how shared genomic regions between humans and apes that were interpreted as relict junk DNA, and used as evidence of common ancestry, have turned out to be highly functional and essential.

 In evaluating the book, there is one area where I am left with a sense of uncertainty. By defining themselves as lumpers, are the authors somehow downplaying the morphological variability observed in the hominin fossil record? For example, the term “anatomically modern human” is often used to characterize fossils in the book. But what does “anatomically modern” mean for a lumper? Is an erectus skull “anatomically modern” because some of its diagnostic traits can also be found in pathological modern individuals? In chapter 11 (the one on the coexistence of australopiths and humans), there is a summary figure (p. 266-267) listing some fossils as “anatomically human” and describing them in the caption as “anatomically modern bones indistinguishable from H. sapiens.” By characterizing in this way a fossil like the LD 350-1 mandible from Ethiopia,[6] for example, are we failing to emphasize the differences from what typically observed in the majority of modern humans (e.g., the absence of the chin bony prominence)? What gets partially overlooked with this approach is the fact that the predominant anatomically modern human cranial configuration (a big, well rounded skull) is not much documented in the Pliocene fossil record. This dearth of fossil evidence should be acknowledged in a creationist model of origins.

Being lumpers, Rupe and Sanford consider modern humans as capable of expressing broad skeletal plasticity. At the same time, however, they are definite splitters when it comes to separating apes from humans in the fossil record, rejecting the notion of mosaicism. Can this clear binary system of classification be confidently applied to diagnose fragmentary fossil material? What skeletal characters (or combination of characters) are reliable indicators? Should characters be treated as discrete or do they occur in a continuum? Do the boundaries of human plasticity never overlap with ape skeletal variability? Which quantitative statistical methods can be trusted to overcome a sense of subjectivity in classification? These are broad questions that transcend the specificity of this book and are foundational to the practice of paleoanthropology.

A second, minor observation concerns two instances where the authors embrace the findings of recent publications that are still being “contested:” the Cerutti Mastodon site[7] (discussed on p. 28) and the Trachilos footprints[8] (mentioned at the end of several of the book’s chapters). Given the current debate surrounding these reports,[9] a cautionary note would seem advisable.

In conclusion, Contested Bones is an accessible, relevant, passionate treatment that is sure to give food for thought and challenge readers to evaluate their presuppositions, no matter which conviction they hold when it comes to the fossil record of humans.

Reviewed by
Ronny Nalin, PhD
Geoscience Research Institute

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Endnotes

[1] Supporting Online Material for Australopithecus sediba: A New Species of Homo-like Australopith from South Africa. Berger, L.R., de Ruiter, D.J., Churchill, S.E., Schmid, P., Carlson, K.J., Dirks, P.H.G.M., Kibii, J.M., (2009). Science 328, 195, p.2.

[2] Supporting Online Material for Australopithecus sediba Hand Demonstrates Mosaic Evolution of Locomotor and Manipulative Abilities. Kivell, T.L., Kibii, J.M, Churchill, S.E., Schmid, P., Berger, L.R., (2011). Science 333, 1411, p.6.

[3] Zipfel, B., DeSilva, J.M., Kidd, R.S., Carlson, K.J., Churchill, S.E., Berger L.R., (2013). The Foot and Ankle of Australopithecus sediba. Science 333 (6048), 1417-1420.

[4] Schmid, P., Churchill, S.E., Nalla, S., Weissen, E., Carlson, K.J., de Ruiter, D.J., Berger, L.R., (2013). Mosaic Morphology in the Thorax of Australopithecus sediba. Science 340 (6129), 1234598.

[5] Barras, C. (2014). Missing link fossils may be a jumble of species. New Scientist 2964, 11.

[6] Villmoare,B., Kimbel, W.H., Seyoum, C., Campisano, C.J., DiMaggio, E.N., Rowan, J., Braun, D.R., Arrowsmith, J.R, Reed, K.E., (2015). Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia. Science 347 (6228), 1352-1355.

[7] Holen, S.R., Deméré, T.A., Fisher, D.C., Fullagar, R., Paces, J.B., Jefferson, G.T., Beeton, J.M., Cerutti, R.A., Rountrey, A.N., Vescera, L., Holen, K.A., (2017). A 130,000-year-old archaeological site in southern California, USA. Nature, 544 (7651), 479-483.

[8] Gierliński, G.D., Niedźwiedzki, G., Lockley, M.G., Athanassiou, A., Fassoulas, C., Dubicka, Z., Boczarowski, A., Bennett, M.R., Ahlberg, P.E., (2017). Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?. Proceedings of the Geologists' Association 128 (5-6), 697-710.

[9] See, for example, Magnani, M., Grindle, D., Loomis, S., Kim, A.M., Egbers, V., Clindaniel, J., Hartford, A., Johnson, E., Weber, S., Campbell, W., (2019). Evaluating claims for an early peopling of the Americas: experimental design and the Cerutti Mastodon site. Antiquity 93 (369), 789-795; Meldrum, J., Sarmiento, E., (2018). Comments on possible Miocene hominin footprints. Proceedings of the Geologists' Association 129, 577-580.