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Comment by laszlojamf | Hacker News Reader

Could be a cliff fitness function. Heard about this relativ typ schizophrenia here on HN a while back. The idea is that some phenotypes promote survival of the species overall, but due to random mutations are sometimes detrimental to individual members of that species

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It could also be indirectly linked to other benefits. Humans have lost the CMAH gene, making us able to run long distances and hunt down large prey animals. But because of this we can no longer process specific sugars that you will still find in mammalian meat. That causes inflammation and arteriosclerosis. But those things only kill you after many decades, so there seems to have been a net positive effect on evolution.

This idea can generally work, but one should be careful of 'just-so' stories in evolutionary biology.

It appears this deletion happens in other animals and may be attributable to pathogen pressure. It's arisen multiple times, which makes it hard to claim that it has a specific role in primates (beyond its presumed antimicrobial benefit, which any animal should enjoy).

https://inflammregen.biomedcentral.com/articles/10.1186/s412...

Evading pathogen pressure is just another benefit behind the scenes. The point is that I would be careful to attribute any of these things to such weird mechanisms when there are so many much more realistic explanations that we just haven't fully uncovered yet.

> Evading pathogen pressure is just another benefit behind the scenes.

I'm imagining that this relates to a specific pathogen that may no longer exist (like the presumed mechanism of the most common cystic fibrosis mutations and cholera).

I'm not sure how this would relate to humans running, however.

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