Calling In Sick

Infectious diseases amongst the Neanderthals may be one factor involved with their disappearance...

Underdown suggests that "there is a potential role for Transmissible Spongiform Encephalopathies (TSEs), [an infection] initially contracted as a result of cannibalism" (Underdown 2007, p. 4) that acted as the catalyst for Neanderthal extinction. TSEs are similar to "Mad Cow Disease" amongst modern Europeans and North American humans and Kuru amongst the Fore of Papua New Guinea in that they all infect the brain tissue and cause degenerative brain disorders. TSEs can occur sporadically, through hereditary transmission, or through contact with tissues of an infected individual (p . 4-5). Incubation periods can be as long as 50 years, and symptoms are varied, from personality changes, jerky movements to loss of speech, complete paralysis and early death (p. 5).

To test the effects of an infectious disease like TSE amongst the Neanderthals, Underdown uses a ethnographic comparison of Kuru amongst the Fore of Papua New Guinea. He draws comparisons based on the fact that TSE and Kuru are similar types of infectious diseases and that Neanderthals and the Fore share a common lifestyle pattern as hunter-gatherers. Albeit a large generalization to compare the two groups based on superficial life patterns, Underdown claims that: "the many shared cultural adaptations of both species substantially reduce the problems of creating such a cross-species model" (p. 5). The fact that Neanderthals and the Fore lived in different climatic regions, had vastly different diets despite the fact that they both foraged and exhibited very different reactions to the introduction of other human populations (archaic Homo sapiens potentially eradicating the Neanderthals; Europeans "conquering" the Fore) apparently do not matter here.

The hypothesis tested is that cannibalism played a role in Neanderthals' contraction of TSE, which led to their demise. Underdown references the relatively accepted cannibalistic evidence at the Neanderthal site of Moula-Guercy (Defleur, White et al. 2006) and states that this could be the catalyst for the initial infection (p. 5).

A 'Kuru Model' is derived from the case study of the Fore to map out mortality rates and rates of contraction of this infectious disease. Based on this model, Underdown claims that if a population were 15,000 in size, "TSE related deaths could reduce the population to non-viable levels within the space of 250 years" (p. 5). He then relates these hypothetical figures to raw data of Neanderthals. The archaeological record suggests that Neanderthals lived in groups of 10-30 individuals. Genetic analysts hypothesize that the "founding" Neanderthal populations would have been approximately 3000 to 10,000 in size. Population density amongst the Neanderthals would have been relatively low, and a total population size of 10-20,000 Neanderthals in Eurasia at any given point in time is assumed (p. 6). If pockets of Neanderthal populations became infected with TSE as a result of cannibalism, this would lead to "a depletion of population numbers of population thinning" (p. 6). Combined with the climactic variation of Oxygen Isotope Stages 5-3 during the end of Neanderthal existence, the "impact on the ability of small-scale Neanderthal groups to cope with the demands of hunter-gatherer based subsistence patterns would have been pronounced" (p. 6).

Underdown ultimately suggests that his hypothesis "does not seek to remove or dismiss the effects of other processes [which may have lead to Neanderthal extinction] but it does highlight that a 'silent killer' in the form of TSEs could have massively weakened the Neanderthals ability to compete both within a highly changeable environment and latterly against a highly adaptable new arrival in the form of Homo sapiens" (p. 6). In conclusion, Underdown states that Neanderthal extinction was probably a series of events that "may have had little causal factors in common" (p. 6). Therefore, if TSE played a role in the extinction of Neanderthals, to Underdown it would represent only one of many factors involved in their mysterious downfall.

Discussion Points

1) Cannibalism within the Fore of Papua New Guinea is widely accepted. However, Kuru disease may have other roots. Despite Arens' misunderstanding of ethnographic and archaeological evidence (see: "No evidence of cannibalism....ever?", March 29th, 2009, posted by Deborah Hayek), he does make a valid point when he suggests that Kuru may have been introduced by European conquerors as they both 'appear' at roughly the same time. If the Fore had been practising cannibalism prior to European arrival (and it is documented that they had), the fact that Kuru was not apparent earlier does suggest a link with European settlement (Arens 1980). Some suggest that Kuru may have only been diagnosed with the arrival of Europeans but may have been prevalent prior (Collinge et al. 2006). As well, the fact that Kuru symptoms appear to have decreased with the observed decrease in cannibalistic behaviour would suggest a link between cannibalism and Kuru. In the end, more research must be done before drawing conclusions on the catalyst for this infectious disease, especially if it is to be used as a model for potential infectious diseases amongst the Neanderthal.

2) The Fore display trends in their mortality rate patterns common in infectious diseases, where mortality peaks in infants and children under 5 years, as well as in the 15-25 years cohort of prime reproducers. The following charts, abstracted from Alpers (2008), present the demographic effects of Kuru on the Fore:

In contrast, Neanderthal mortality patterns do not indicate infectious disease as infants and children appear to have low mortality patterns. General data on Neanderthal mortality patterns is limited, but Trinkaus (1995) did compile information from 206 archaeological sites. These sites by no means encompass all known Neanderthal sites and the mortality rates found within the Neanderthal archaeological record cannot be construed as an exact reflection of living society because preservation is not necessarily population representative. However, for the sake of providing some terms of comparison, here is an overview of Neanderthal mortality patterns derived from the archaeological record:

The differences between mortality patterns within the Kuru-infected Fore and the Neanderthals suggest that the latter were not subject to an infectious disease like TSE. However, this is based solely on the supposition that the Neanderthal archaeological record is a relatively just representation of general Neanderthal mortality patterns. In addition, the 'Kuru Model' incorporates rates of contraction which would be impossible to hypothesize for Neanderthals.

This paper incites further lines of research that have yet to be examined, such as:

1) Can mortality patterns at Moula-Guercy alone, postulated by Underdown as the birthplace of a TSE outbreak, tell us whether an infectious disease did erupt among the Neanderthals? Would this have meaning if TSE theoretically should have impacted every Neanderthal group?

2) Is it theoretically possible for the Neanderthal rates of mortality in the archaeological record to have skewed real mortality rates completely? If so, would an infectious disease be credible amongst the Neanderthal?

3) Can mortality patterns alone represent the rate of infection of a disease like TSE or Kuru, where incubation can last for up to 50 years and symptoms do not always lead to an early death?

4) Can the final cause or series of causes of the Neanderthal extinction ever be definitely found?

Resources:

Alpers, M. P. 2008. The epidemiology of kuru: monitoring the epidemic from its peak to its end. Philosophical Transactions of the Royal Society B 363: 3707-3713.

Arens, W. 1980. The Man-Eating Myth. Oxford University Press, USA.

Collinge J., J. Whitfield, E. McKintosh, et al. 2006. Kuru in the 21st century - an acquired human prion disease with very long incubation periods. The Lancet 367: 2068-2074.

Defleur, A. A., T. White et al. 2006. Neanderthal Cannibalism at Moula-Guercy, Ardeche, France. Science 286: 128-131.

Trinkaus, E. 1995. Neanderthal Mortality Patterns. Journal of Archaeological Science 22: 121-142.

Underdown, S. 2007. A potential role for Transmissible Spongiform Encephalopathies in Neanderthal extinction. Medical Hypotheses 71: 4-7.