A Neanderthal-eat-Neanderthal world may have spread a mad cow-like disease that weakened and reduced populations of the large Eurasian human, thereby contributing to its extinction, according to a new theory based on cannibalism that took place in more recent history.
Aside from illustrating that consumption of one's own species isn't exactly a healthy way to eat, the new theoretical model could resolve the longstanding mystery as to what caused Neanderthals, which emerged around 250,000 years ago, to disappear off the face of the Earth about 30,000 years ago.
"The story of Neanderthal extinction is one of the most intriguing in all of human evolution," author Simon Underdown told Discovery News. "Why did a large-brained, intelligent hominid that shared so many traits with us disappear?"
To resolve that question, Underdown, a lecturer in the Department of Anthropology at Oxford Brookes University, studied a well-documented tribal group, the Fore of Papua New Guinea, who practiced ritualistic cannibalism.
Gory evidence uncovered in a French cave in 1999 revealed Neanderthals likely practiced cannibalism. The 100,000-120,000 year-old bones discovered at the cave site of Moula-Guercy near the west bank of the Rhone river suggested a group of Neanderthals defleshed the bones of at least six other individuals and then broke the bones apart with a hammerstone and anvil to remove the marrow and brains.
Although it's not clear why Neanderthals may have eaten each other, research on the Fore determined that maternal kin of certain deceased Fore individuals used to dismember corpses and regarded some human flesh as a valuable food source.
Beginning in the early 1900's, anthropologists additionally began to take note of an affliction named Kuru among the Fore. By the 1960's, Kuru reached epidemic levels and killed over 1,100 people.
Subsequent investigations determined that Kuru was related to the Fore's cannibalistic activities and was a form of Transmissible Spongiform Encephalopathy, or TSE. This is a class of disease that includes mad cow disease. Underdown said TSE's have been in existence for possibly millions of years.
According to his new paper, published in the journal Medical Hypotheses, TSE's "cause brain tissue to take on an almost sponge-like appearance, caused by the formation of small holes during the development of the disease."
The disease's latter stages often result in severe mental impairment, loss of speech and an inability to move.
He created a model, based on the Kuru findings, to figure out how the spread of such a disease via cannibalism could reduce a population's size. For example, he calculated that within a hypothetical group of 15,000 individuals, such a disease could reduce the population to non-viable levels within 250 years.
When added to other pressures, this type of disease could therefore have wiped out the Neanderthals, Underdown believes.
"TSE's could have thinned the population, reducing numbers and contributing to their extinction in combination with other factors (such as climate change and the emergence of modern humans)," he said.
Such diseases have very long incubation periods, he further explained, so affected individuals may not show symptoms for a very long time. Similarly, people who consume TSE victims may not exhibit signs of illness immediately after eating.
"Neanderthals would have been unlikely to spot any causal relationship between cannibalism and TSE symptoms," Underdown said.
Since modern clinical tests show that medical instruments can carry infectious prions, which spread TSE's, even after such tools have been sterilized, it's also possible that sharing of stone tools could have additionally spread the disease among Neanderthals, even those that did not practice cannibalism.
Nick Barton, Director of the Institute of Archaeology at the University of Oxford, told Discovery News that he thinks the new paper presents "an extremely novel and very interesting theory."
"Most scholars now believe that the demise of the Neanderthals was not down to a single causal factor," Barton said. "However, if genetic studies eventually show that Neanderthals were susceptible to TSE, or other empirical evidence emerges for persistent cannibalism and consumption of brain tissues in late Neanderthal populations, then we may have to rethink our ideas on extinction."