THURSDAY, April 10, 2003 (HealthDayNews) -- Our ancestors may have been indulging in more "brain food" than we thought, which might have been good for them and for us.
The discovery of genes that protect against prion diseases has led British researchers, writing in the April 11 issue of Science, to suggest that cannibalism among our prehistoric forebears may have been widespread.
Others think the theory is a bit farfetched.
"That is a real stretch," says Dr. Paul Brown, senior investigator with the National Institutes of Health, who did similar research and published it two years ago in the Journal of Infectious Diseases.
Prions are a certain type of protein which, when present normally in the human body, cause no harm. When the prions fold into a different shape, however, they can cause Creutzfeldt-Jakob disease (CJD, or the human equivalent of "mad cow" disease) and other so-called prion diseases. These diseases cause brain degeneration and eventually death and can, in fact, be spread by eating contaminated body parts, human or otherwise.
Creutzfeldt-Jakob disease is simply the most recent example of the phenomenon. Another prion disease, called kuru or "laughing death," caused consternation earlier in the century.
The Fore people of Papua New Guinea devoured their dead relatives as a routine part of the funeral services. "It was an act of honor and incorporation," Brown reports. "One way to achieve immortality is to become part of a still living person."
According to interviews with villagers conducted by Dr. D. Carleton Gajdusek, who later won a Nobel prize for his work, the practice began after the turn of the century and probably closer to 1920. "That observation is consistent with the notion that a random CJD case got eaten and rapidly, by recycling, caused an epidemic," Brown says. Children of both sexes as well as young adult women were most affected, as they were the ones handling the tissue and also the ones most likely to eat the brain (which, along with nervous system tissue, is the most common reservoir of prions).
Australian administrative authorities banned cannibalism in the mid-1950s and the incidence of kuru declined thereafter. According to the study authors, from University College London and elsewhere, kuru still occurs, but only in older individuals and probably is a reflection of a long incubation period.
The authors of this study, like Brown before them, studied genetic samples from the population that was exposed to kuru and from a more recent population (from the same region) that was not exposed. "We found a very striking difference," Brown says. "The difference was that the population today has a very reduced proportion of homozygotes."
Homozygotes, or people with one each of two different genes, are known to be more susceptible to prion diseases. Heterozygotes, or people with two of the same gene, are less likely to get a form of the disease.
"Our results led us to conclude that the reduction in the number of homozygotes we see in this Fore population today is the result of a disproportionate number of homozygotes having been killed by kuru," Brown says. "It's very straightforward. If you have one genotype that's more susceptible than another to a particular disease, the susceptible genotype will tend to disappear."
The same process appears to be at work with Creutzfeldt-Jakob, as more homozygotes tend to develop the disease.
By the study authors' reckoning, the prevalence of cannibalism among our prehistoric ancestors would have increased the number of heterozygotes and decreased the number of more fragile homozygotes. In other words, you needed strong genes to survive to see your next human meal.
Nowadays, you just need to avoid central nervous system and brain tissue form contaminated bovines.
More information
For more on Creutzfeldt-Jakob disease, visit the CJD Foundation. For more on Carleton Gajdusek, who won the 1976 Nobel Prize in Medicine, visit the Nobel site.
