Cannibalism: A Perfectly Natural History(78)
I was reminded of earlier studies in which lab chimps did not become infected with kuru after being fed infected material through a gastric tube. “So you’re saying that these seemingly immortal proteins can be broken down by our own digestive juices?”
“They’re not immortal,” Manuelidis replied. “And yes, all detectable forms of PrP are digested in the gastrointestinal tract, yet the invasive infectious particle [that causes TSEs like kuru] is not destroyed.”
“The same way that many viruses aren’t destroyed in our GI tract?”
“Right.”
If this was in fact true, then how were the prions, which researchers like Prusiner claimed to be the cause of kuru, getting past a gastrointestinal tract that had evolved to digest dietary proteins? At the very least, if prions did exist, then their spread through the Fore via cannibalism no longer made sense—since their digestive tracts would have broken down the proteins during the normal process of digestion. But if the infective agent causing kuru had been a virus, then transmission through the practice of ritual cannibalism made even more sense, since viruses weren’t broken down by our digestive systems.
Although the majority of the scientific community had clearly accepted prions as the pathogens behind a range of neurological diseases, there are still some strong voices besides Manuelidis’s opposing this view. In a new afterword of his 1998 book, Deadly Feasts, Richard Rhodes admitted to being intrigued by the very real possibility that Dr. Manuelidis could be right.
“I raise the virus issue,” he wrote, “partly because I now believe I gave it less than a fair hearing in the body of this book and partly because the arguments I’ve heard in its favor since I wrote, especially from Laura Manuelidis, seem to me compelling.”
Clearly there remains much for science to explore regarding transmissible spongiform encephalopathies. One can only hope that the funding agencies that poured tens of millions of dollars into prion-related research will not see this story as a fait accompli or that researchers who challenge the very existence of self-replicating, infectious proteins won’t have their voices silenced by skittish granting agencies or peer reviewers, perhaps too set in the conviction that prions are the cause of transmissible spongiform encephalopathies from kuru to mad cow disease and beyond.
* * *
52 According to Noel Gill, lead investigator of the “Appendix” study, further research is now underway to determine whether prion proteins also occurred in samples from the 1970s and earlier—before the appearance of BSE in the UK. Such a finding could reduce the significance of the 2013 study, since it would suggest that prion proteins in a population do not necessarily translate to a major outbreak of spongiform encephalopathy.
Epilogue: One Step Beyond
Hunger hath no conscience.
— Author unknown
Cannibalism makes perfect evolutionary sense. If a population of spiders has an abundance of males from which a female can choose, then cannibalizing a few of them may serve to increase Charlotte’s overall fitness by increasing the odds that she can raise a new batch of spiderlings. On the other hand (and in spiders there are eight of these to choose from), in a population where males aren’t plentiful or where the sexes cross paths infrequently, cannibalizing males would likely have a negative impact on a female’s overall fitness by decreasing her mating opportunities. As a zoologist, I find this kind of dichotomy pleasing, since it’s logical and appears to be more or less predictable in occurrence. In nature, as far as cannibalism is concerned, I’ve found no gray areas, no guilt, and no deception. There is only a fascinating variety of innocent—though often gory—responses to an almost equally variable set of environmental conditions: too many kids, not enough space, too many males, not enough food. The real complexity and the uncertainty didn’t kick in until I shimmied out farther onto our own branch of the evolutionary tree. It was here that I found cannibalism painted in equal shades of red and gray.
Sigmund Freud believed that in humans, atavistic urges like cannibalism and incest are hidden below a veneer of culturally imposed taboos, and that the suppression of such forbidden behaviors signaled the birth of modern human society. This is a compelling explanation, but it’s one that likely requires some serious tweaking.
Compared to other groups such as insects and fishes, cannibalism occurs less frequently in mammals and even less frequently in our closest relatives, the primates—where most examples appear to be either stress-related or due to a lack of alternative forms of nutrition. Though we humans do share some of our genetic makeup with fish, reptiles, and birds, we’ve evolved along a path where cultural or societal rules influence our behavior to an extent unseen in nature. Freud believed that these rules and the associated taboos prevent us from harkening back to our guilt-free and often violent animal past. Similarly, my studies have led me to conclude that the rules we’ve imposed in the West regarding cannibalism serve as constraints to behavior that might otherwise be deemed acceptable if we were looking at protein-starved Mormon crickets instead of indigenous Brazilians consuming their unburied dead.
There is a considerable body of evidence that cultures that were never exposed to these taboos (like Homo antecessor) or encountered them only relatively recently (the Chinese and the Fore of New Guinea) had no such problems undertaking a range of cannibalism-related behaviors as they developed their own sets of rules and rituals. Much to our Western dismay, some of these cultural mores extolled the virtues of cannibalism as an honor bestowed upon a deceased relative or a slain foe, or as a respectful way to treat a gravely ill parent. But even in societies where cannibalism might once have been a perfectly acceptable practice, given the pervasive influence of Western culture across the world, it’s unlikely that ritual cannibalism currently exists, even on a small scale.