|Fore People of Papua New Guinea.|
Until the late 1950s the Fore people of Papua New Guinea had an unusual way of honouring their dead - they ate them, or more particularly, they ate their brains in a funeral ritual. This ritual meant that they caught kuru, a disease of the brain which killed some 2500 Fore before its cause was identified and the practice was stopped.
Kuru is caused by a prion and is invariably fatal. It is closely related to the prion which causes 'mad cow' disease in cows, scrapie in sheep and Creutzfeldt-Jakob disease in humans. These are also caused by eating brains and central nervous system tissues and was caused in humans in the UK when the government deregulated the animal feed industry, making it permissible for ground-up dead animals, including sheep which had died of scrapie, and even dead cows, to be fed to cattle and other farm animals. Scrapie crossed the species barrier to produce 'mad cow' disease, which then crossed the species barrier again to produce variant Creutzfeldt-Jakob disease (vCJD) in humans, of which 166 people have so far died.
They found a mutation in 51 of the survivors and their descendants which was not found in a single victim of kuru. This mutation is in the gene which codes for the prion protein PRNP which, when it becomes deformed, causes other proteins to also become deformed, destroying the brain in a chain reaction which proceeds exponentially. The mutation appears to prevent the formation of disease-causing prions.
This mutation arose about 200 years ago by accident in a single individual and was inherited by his or her descendants so that, about 100 years ago when the kuru epidemic was at its height, there were just a couple of families who were carriers of the mutant gene. They and their descendants survived whilst many of the non-carriers died, so, under intense selection pressure, the frequency of the mutant allele increased hugely in the gene pool in just a few generations.
I hope it will become a textbook example of how evolution happens. It's a striking and timely example, given the 150th anniversary of the publication of Darwin's Origin of Species.Interestingly, this example gives the lie to three Creationist assertions:
Simon Mead - one of the team of researchers
- Evolution doesn't happen.
- Mutations are always harmful.
- No new information can arise by mutation.
Here we see a beneficial mutation rapidly increasing in a population by a simple process of Darwinian evolution by natural selection. And of course we also see how environmental context gives meaning to a change in information in the genome. In the absence of kuru, the mutation would have been devoid of meaning.
Evolution Via Cannibalism: The Case Of Kuru (Science Life)
Kuru Field Studies in Papua New Guinea (MRC Prion Unit)
Gene Change In Cannibals Reveals Evolution In Action (New Scientist)