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Sci Tech
Were we cannibals long ago?
DID MAN ever eat man? He eats just about every form of life — fungus, bacteria, plants, insects and animals in water, land or air. Is there a biological difficulty about it, or is it a cultural restriction? Many animals do it, some of them eating their own young. Alex Pacheco, the Chairman of People for the Ethical Treatment of Animals, writes that he had seen starving dogs eat their own kind. In the book "Chimpanzee Politics: Power and Sex among the Apes", authors Frans de Waal and Desmond Morris claim that the great apes too practice cannibalism, albeit less frequently. Did evolution equip us to eat other men, and culture stop it?
Historical accounts on cannibalism are not clear, since they are invariably mixed with prejudice, self-aggrandisement of the colonial and religious or cultic pronouncements. Columbus chronicled that he encountered a man-eater tribe called the Caniba in the Caribbean, and that gave us the term cannibal. It is not clear whether the caniba really ate their fellow men, or whether this was an allegation by an unfriendly neighbouring tribe. In any event, Pope Innocent IV decreed it to be a sin, which led Queen Isabella to order the Spanish colonialists to legally enslave natives thought to be cannibals. This provided the licence, plus the economic interest, to the colonists in making such allegations and conquer territory.
A dispassionate and unprejudiced history of cannibalism is hard to come by. Whenever someone in history reported that they saw men eating human flesh, it was not clear whether it was because of lack of any other food, or done in a more token or ritualistic manner for cultural, religious or medicinal purposes. The fierce Bhairavas of Tantrik Hinduism seem to engage in it, using blood and certain other parts ceremonially. Medieval European medicine men prescribed blood and certain other parts of the human body as cures for epilepsy, porphyria, and arthritis. And the tribe called Fore in Papua New Guinea, chronicled to be man-eaters, appear to do so as part of a religious ritual. The Nobelist Dr. Carleton Gajdusek, who studied a particularly deadly form of brain disease called Kuru among the Fore people, kept a detailed dairy on his visits and stay there. He found that the family and neighbours of a dead Fore ceremonially chewed on the dead person's brain in order to ensure a safe after-life for the deceased. Not studying a practice in context and in detail can lead one to jump into conclusions that would support preconceived notions.
It is thus not clear whether the practice occurred due to biological demands of hunger, or cultural reasons. I should like to believe the latter, at the risk of being thought of as a wimp with a notion in mind. But it now transpires that there may be a biological disadvantage or risk in at least certain types of this practice. Dr. John Collidge of University College London got together with colleagues in Western Australia, and Goroka in Papua New Guinea, to study genetic aspects of the `cannibalistic' practice of the Fore people.
Kuru is a brain disease, a neurodegenerative disorder that wastes the affected person horribly - the equivalent of Scrapie in sheep and the Mad Cow Disease of cattle. Dr. Gajdusek showed that this occurs due to a "slow acting virus" that was present in the flesh of the deceased. It has now become clear that the pathogen is not a DNA virus nor an RNA virus, but actually a malformed miniature protein called a prion (named so, to sound similar to `virion' for a virus). Misfolded prions act as seeds or nuclei, forcing other, native prions, also to misfold and clump together into fibrous masses which kill brain cells. The Cruetzfeldt- Jacob Disease (CJD) is thought to be caused in a similar manner, as are Scrapie and Mad Cow Disease. A normal protein in the nervous system, called Prp-C loses its normal shape in the disease, turning into a misfolded wrongly-shaped form, termed Prp-Sc. This sets out a chain reaction, recruiting more and more of normal Prp-c, misfolding and aggregating it into an insoluble Prp-Sc. Insoluble like the scales in a coffee kettle, or plaque formed on teeth, this is called the amyloid plaque, and causes brain cells to misfire and die.
Collidge and group focused on the gene (called PRNP) that codes for the prion protein in humans and went over to Papua New Guinea to study the PRNP profile of the Fore people. Kuru no longer affects them, because of a ban on `cannibalism' imposed by the Australian authorities there in the 1950s. Collidge decided to look at the PRNP genes in elderly Fores who had practised the ritual before the ban, and in young Fores who had never done it. For comparison, the PRNP gene profiles of `control' populations from Japan, India, Sri Lanka, Africa, Europe and Colombia were also studied. The idea was to compare the gene sequences and mutations, so that the genetic aspects of Kuru could be understood. The approach here is similar to a similar analysis done on CJD patients earlier. In that instance, it was found that the people carrying two identical copies of the gene for the prion protein (PRNP) are more susceptible to developing CJD than those who carry two unmatched variants. This mismatch seems to protect people against the disease.
When the gene sequences were compared, now for Kuru, Collidge found that all ethnic groups carried two unmatched variants of the prion gene. The fact that the variants are so widespread suggests that they have been conserved throughout human history. Based on further comparisons, and comparison with the chimpanzee DNA, the scientists estimate that the variants in the gene arose about 500,000 years ago, during the era of prehistoric ancestors of us modern humans. For most genes, one variant is beneficial for fitness more than the other. The less beneficial disappears over time. Thus, there is a selection pressure due to adaptation.
Among Fore, the number of women carrying one copy of each variant (heterozygotes) instead of two copies of one or the other, was particularly high. This suggests that having one copy of each variant protected many members of the Fore tribe against Kuru. This is what Collidge refers to as "balancing selection". Some genes are selected thus, the haemoglobin gene being an outstanding example. One variant of the globin gene causes sickle cell anaemia in a person who carries two copies of it (one from each parent), but the variant persists because it protects against malaria if it is coupled with another variant.
But the fact that prion gene variants persist in humans across the world suggests that prion diseases were widespread in early human history. The group also suggests that frequent epidemics of prion disease caused by cannibalism in ancient humans would explain existence of protective gene signature ( variant pairing) among today's humans. This is perhaps why, of the 50 million people in England, only 134 fell victim to the Mad Cow Disease, eating prion-contaminated beef; so says Dr Simon Mead of Prion Unit of MRC England, who worked with Dr Collidge. So, was cannibalism prevalent in ancient human history? Collidge thinks so, and Dr. Tim White of the University of California Berkeley says archeological evidence might support the idea. But anthropologists are not convinced and argue that evidence from their field is lacking. We have to wait more in future to know what we did in the past.
D. Balasubramanian
dbala@lvpeye.stph.net
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