Human ovulation lacks visible signs, unlike chimpanzees and bonobos with conspicuous genital swellings during fertility. This led to the concept of "concealed ovulation," seen as a human adaptation. Proposed reasons include encouraging paternal investment, confusing paternity to deter infanticide, enabling secret mating and female choice, and reducing female rivalry. Many non-human primates also have unsignaled ovulation. While self-reported human mating doesn't match ovulation, debates persist on subtle reproductive cycle influences. Some cultures use menstrual taboos to disclose fertility status. (#39275)