1. Lactose tolerance in adulthood. Lets an adult drink cow milk without getting gassy or feeling sick. Cow milk has all sorts of good stuff in it and probably drinking it can help a woman support a pregnancy.
2. Sickle cell anemia allele. The heterozygotes don't die of malaria or sickle cell anemia. This is a "heterozygote advantage" in parts of the world where mosquitoes carry malaria.
3. Straight black hair. Sexual selection decoration (historical). People in parts of Asia who had blond or white hair could never get married -- they were discriminated agains
