SMART NEWS

How Common Was Cannibalism?

July 18, 2012

The Donner party wasn’t so unusual. Throughout history, humans in distress have turned to the tasty morsels next to them—other humans. While eating one another is understandable if stranded on a snowy mountain or desolate wasteland, evidence exists that people also indulged in the practice even when not faced with life-or-death situations.

Slate explores whether day-to-day cannibalism was motivated by religious beliefs or whether people ate people just because they taste good.

Cannibalism per se isn’t bad for you; you can even spoon up and eat most human brains safely. But if your guest of honor happened to suffer from Creutzfeldt-Jakob or another prion disease, those misshapen proteins can slither into your own gray matter when you eat him. This exact scenario unfolded in Papua New Guinea last century, among some highland mountain tribes who consumed their relatives in ritual funeral feasts.

Recently, researchers noticed a strange similarity between Creutzfeldt-Jakob in Papua New Guinea and mad cow disease in the UK. Both diseases wrecked havoc on the brains of people with two copies of the same naturally-occurring prion gene, ATG. Others who had a mutant strain of the prion—GTG—lived healthily for years or never manifested symptoms, despite consuming infected tissue.

The shapes made a difference only when people ate tainted brains, and faced an invasion of the infectious vampire prions. While the bad prions could latch onto one of the two shapes just fine, the other shape could shrug them off and avoid corruption. Overall, then, having two different versions of the prion gene slowed the destruction down.

The prion gene is highly conserved—it doesn’t change much as it passes from generation from generation. Of the 100+ mad cow deaths in the UK, all the victims except one had identical copies of the prion gene rather than one of the mutant strain, GTG. And follow-up work revealed the mutant strain pops up in populations all over the world. The researchers conclude that having two different copies of the prion gene—ATG and the mutant GTG—gives the bearer some protection against prion diseases spread through munching on infected brains.

One group of scientists argued that our ancestors needed that protection because of their cannibalistic ways, Slate reports:

How did GTG spread so far? Perhaps through genetic drift, a random diffusion process. Or perhaps—as a few scientists argued in a controversial paper from 2003—cannibalism was so popular in our past that all human ethnic groups had to stockpile alternative versions of the prion gene or else they’d get wiped out.

Some scientists are critical of the 2003 paper, however, claiming that it overestimates our past propensity for eating one another.

But even these critics acknowledge that the prion gene has a strange history, and that outbreaks of cannibalism like the one in Papua New Guinea could well have altered the DNA of many ethnic groups. And regardless of exactly why the exotic versions of the prion gene spread, the fact that they have means that many of us can now taste the most forbidden flesh of our fellow human beings with relative impunity. Only problem is, they can do the same to you.

In other words, even as we devour one another like so many zombies, evolution continues to tick away, finding ways to save us from our own self-destructive and twisted tendencies.