Mad Neanderthal Disease?

The impact of Transmissible Spongiform Encephalopathies (TSE) on Neanderthals is the topic of a short paper by Simon Underdown (2008), in press in Medical Hypotheses. You might be familiar with TSEs already: a few years back, the so-called “Mad Cow Disease” scare was caused by Bovine Spongiform Encephalopathy.

Getting back to the study at hand, the gist of the paper is this:

1) Neanderthals are known to have practiced cannibalism.

2) Cannibalism is known to result in TSEs in certain cases.

3) In at least one Homo sapiens hunter-gatherer group (in this case the Fore of New Guinea), the relationship between cannibalism and some kind of fatal degenerative neurological disease has been credibly established (the 'Kuru' epidemic'; Farquhar and Gadjusek 1981).

4) Therefore, it is possible that TSEs transmitted through cannibalism and handling dead Neanderthal tissue contributed to the ‘extinction’ Neanderthals, to wit: “… a silent killer in the form of TSEs could have massively weakened the Neanderthal’s ability to compete both within a highly changeable environment and latterly against a highly adaptable new arrival in the form of Homo sapiens” (Underdown in press: p.3).

The paper itself does a much better job of contextualizing this conclusion than headlines related to the diffusion of this study such as “Cannibalism wiped out Neanderthals” which is overly sensationalistic on top of fostering the curious image of Neanderthals eating one another into oblivion (which would certainly put a new spin on the old ‘competition with moderns over animal resources’!).

And, while it is nearly impossible to conclusively disprove many paleoanthropological hypotheses, it is certainly possible to evaluate their plausibility, and the case for TSEs as a, errr, vector in Neanderthal extinction is improbable. First, the use of the Fore as the single analog is problematic on several levels: they are horticulturalists, a poor analog for highly mobile hunter-gatherers; the kuru epidemic on which Underdown’s scenario depends unfolded over a span of only decades whereas he postulates that TSEs would’ve plagued Neanderthals for millennia; and, importantly, the Fore live at population densities (about 21/km²), orders of magnitude greater than those likely to have characterized, and certainly those proposed for them by Underdown (ca. 0.06-0.1/km²).

Second, the ‘Kuru Model’ is based on one case of a TSE decimating a single population. That is to say, not all cannibalism needs to result (or have resulted) in the development and rapid transmission of TSEs among its practitioners. This is a problem of extrapolating from one documented case among modern humans (ironically enough) to the entirety of Neanderthal groups. This is a common logical flaw whereby Neanderthals are not considered as comprising a multitude of groups of hunter-gatherers spread over a vast range and likely relatively well adapted to their local conditions. Neanderthals (or any fossil human species, for that matter) are not just a species of extinct hominins; that label refers to biologically similar hominins spread far and wide across Eurasia and whose primary adaptations to their environment were behavioral in nature. Think of it this way: do all Homo sapiens behave exactly the same across the world today? No, and neither did they in the past. This is why there is so much debate over how to satisfactorily define “behavioral modernity” and why we can’t just talk about modern humans acting in one way. The same was very likely true for Neanderthals.

Third, the two best-publicized cases of Neanderthal cannibalism (i.e., Krapina, and Moula-Guercy) go back to 100-80 kya at the most recent. There is, as far as I know, little in the way of strong evidence for widespread Neanderthal cannibalism after that; although clear anthropic modifications of Neanderthal remains have been documented at later sites, such as El Sidrón (Rosas et al. 2006), the case for cannibalism there has not been demonstrated since these have not been shown to be similar to those found on other animal remains at the site. Thus, there is little evidence that cannibalism was a widespread Neanderthal behavior around for the 50 ky that led up to their disappearance from the Eurasian fossil record. Interestingly, there is also some very suggestive evidence that Mousterian sites increased in density over the course of that time period (e.g., van Andel et al. 2003), as opposed to steadily decreasing in numbers as implied by the Underdown’s TSE model.

Fourth, there is clear evidence of perimortem processing of Homo sapiens remains with stone tools is also reported from the Aurignacian deposits of Brassempouy, Isturitz, Tarté and La Combe, where human teeth were forcefully removed from their gums and pierced to be transformed into ornaments (White et al. 2003), and in the Middle Stone Age deposits of Herto, where human skulls bear unambiguous traces of defleshing (Clark et al. 2003). Given that Underdown (in press: p. 3) states that TSEs can well have been transmitted “through cuts caused by stone tools used by infected and non-infected individuals,” shouldn’t we therefore also assume that TSEs would have been a major concern for modern humans as well?

Overall, then, while TSEs might well have been a problem for some groups of Neanderthals and some groups of Homo sapiens, there is no reason to assume that it was an especially important factor leading to the disappearance of Neanderthals as a distinct fossil hominin in the paleoanthropological record. I will say this, however: theoretically at least, Underdown’s scenario has the merit of having the potential to be tested empirically and independently through genetic studies. In that sense, it is a move forward in paleoanthropology.

References:

Clark, J.D., Y. Beyene, G. WoldeGabriel, W.K. Hart, P.R. Renne, H. Gilbert, A. Defleur, G. Suwa, S. Katoh, K.R. Ludwig, J.-R. Boisserie, B. Asfaw and T.D. White, 2003. Stratigraphic, chronological and behavioural contexts of Pleistocene Homo sapiens from Middle Awash, Ethiopia. Nature 423:747–752.

Farquhar, J., and D. Carleton Gajdusek. 1981. Kuru. Early Letters and Field-Notes from the Collection of D. Carleton Gajdusek. New York, Raven Press.

Rosas A, Martínez-Maza C, Bastir M, García-Tabernero A, Lalueza-Fox C, Huguet R, Ortiz JE, Julià R, Soler V, de Torres T, Martínez E, Cañaveras JC, Sánchez-Moral S, Cuezva S, Lario J, Santamaría D, de la Rasilla M, and Fortea J.2006. Paleobiology and comparative morphology of a late Neandertal sample from El Sidron, Asturias, Spain. PNAS 103:19266-19271.

UNDERDOWN, S. (2008). A potential role for Transmissible Spongiform Encephalopathies in Neanderthal extinction. Medical Hypotheses DOI: 10.1016/j.mehy.2007.12.014

van Andel, T. H., W. Davies, and B. Wenninger. 2003. The human presence in Europe during the last Glacial Period I: Human migrations and the changing climate. In Neanderthals and Modern Humans in the European Landscape during the Last Glaciation, pp. 31-56. McDonald Institute of Archaeology, Cambridge, UK.

White, R. W., D. Henry-Gambier and C. Normand. 2003. Human-tooth ornaments from the French early Aurignacian: implications for early Upper Paleolithic treatment of the dead. Paper presented at the 2003 Annual Meetings of the Paleoanthropology Society, Tempe, Arizona.