Comment by gaoshan | Hacker News Reader

Comment by gaoshan | Hacker News Reader

One line that got me wondering: "...and one group ate their dead relatives’ brains at funerals so consistently that they gave themselves a mad cow type disease called kuru, which killed a large percentage of their population and then, within a few generations, evolved a genetic mutation that protects against it"

I had heard this before but my question now is, did they develop this tradition recently? If it were a historical thing wouldn't that genetic mutation have evolved a long time ago? One would expect that if they had this tradition for a long time the genetic mutation that happened so rapidly would have happened long ago, yet it did not. I'm curious as that thought struck me just now.

CJD develops in about 1/1,000,000 people per year globally, and the Fore people have a population of ~20,000. In theory, that suggests there should be an outbreak within 50 years of the society regularly consuming brain matter. Perhaps that number could be reduced somewhat by the infection rate, but the infection rate seems pretty high, to reach the level it did as fast as it did each person with Kuru needed to infect 1.6 people. Perhaps sporadic CJD isn't as sporadic as we assume, and it's tied to being in environments where others have had CJD? Another possibility is tied to the seeming link between genetics and the infection rate of Mad Cow Disease. Perhaps the population regularly went through boom-bust cycles, where everybody with 2 copies of the recessive gene that makes one more susceptible to transmission gets killed off, then the disease dies off for a long enough time for the carriers to re-introduce their recessive trait back into the gene pool.

At least according to this article[1], you're correct; the practice of eating brains that caused kuru to spread was a recent innovation. However, the article doesn't say how recent. I guess I'd need to go read the actual book, since I can't quickly find anything else on how long this was occurring.

[1] https://www.astralcodexten.com/p/your-book-review-the-family...

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