Comment by akoboldfrying
4 hours ago
1. How is it advantageous?
2. Assuming it really is: Why would this make it unlikely to be encoded on a single gene? As a layman, the only condition I'm aware of with this "downside but also upside" quality is sickle cell anaemia (downside is anaemia, upside is increased resistance to malaria), which is decided by a single nucleotide change on chromosome 11.
> As a layman, the only condition I'm aware of with this "downside but also upside" quality is sickle cell anaemia
Essentially all traits that you might think of as "traits" and not "features of the species" have downsides and also upsides. Where there's any significant imbalance, the genes for that trait will be purged from the gene pool (if the trait is basically all negatives) or sweep to become universal (if all positives).