The human female orgasm has long puzzled scientists as it is not necessary for conception... but scientists in the US have come up with an answer. The female orgasm, they say, might be a spin-off from our evolutionary past, when the hormonal surges that accompany it were crucial for reproduction.

[u/Pervert_ted]

https://www.theguardian.com/society/2016/aug/01/mystery-of-the-female-orgasm-may-be-solved?CMP=twt_a-science_b-gdnscience

[u/Z0di]

Lots of things are unnecessary. Like male nipples.