[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.