I see what you are getting at - but it's all about pressure and selection. For instance Sickle Cell anemia is hypothesized to actually be a defense we evolved

I see what you are getting at - but it's all about pressure and selection. For instance Sickle Cell anemia is hypothesized to actually be a defense we evolved against malaria: https://en.wikipedia.org/wiki/Human_genetic_resistance_to_malaria https://en.wikipedia.org/wiki/Human_genetic_resistance_to_ma... People that had that mutation were better able to fight off malarial infections in those environments where it was prevalent - and those genes now are passed on specifically in certain ethnicities, etc.