[vidarh]

Without access to modern hospital treatments it is fairly normal to die very young from sickle cell disease - it causes 100k+ deaths a year.

An in-law of an ex has it, and regularly spends days in hospital during crises. Without access to a high quality hospital he'd have been dead a long time ago.

The average life expectancy for someone with sickle-cell disease in developed countries is 40-60 years, and serious crises tend to start from childhood.

That said, it's recessive, and so it's likely the reverse of what you think: It's not primarily the people with full-blown disease who contributes most to the long term survival of the trait, but that the trait alone confers fairly significant advantage in regions where Malaria is huge killer mostly without causing health problems. So across the combined set of carriers and those with the full disease, the life expectancy in Malaria stricken areas tends to be higher.

Pattern of change of the prevalence of the trait correlating with changes in prevalence of Malaria has been observed many places. E.g. the prevalence among US black people is significantly lower and dropping than in the areas their ancestors came from.

[interroboink]

I think this is right, but just to spell out the recessive gene implications for readers, here's the Punnnett square[1] :

      R  | r
    +----+----+
  R | RR | Rr |
  --+---------+
  r | Rr | rr |
    +---------+

The people with sickle cell disease are "rr" — that's 1/4 the population.

The people who have some malaria resistance are all of the ones with "r". In particular, the "Rr" folks have the resistance, but not the anemia.

So basically, this gene screws over 1/4 of the population and benefits 1/2. In areas with lots of malaria, this tradeoff is worthwhile, evolutionarily speaking.

One of those harsh cases where evolution (if we personify it) does not care about individuals — only the species.

[1] https://en.wikipedia.org/wiki/Punnett_square

[__loam]

Worth noting punnet squares are kind of bunk: https://youtu.be/zpIqQ0pGs1E?si=SDRQP-PW2u_6Jq3d

Although sickle cell does seem to be one of the rare cases where they work out.

[wizzwizz4]

Punnet squares are as "bunk" as Ohm's Law.