Are human women’s boobs so large because of evolution?

Humans seem to be the only mammals whose boobs are prominent the whole time, so did they evolve like that entirely for sexual attractive reasons?

I just was thinking that it must be a bit weird for half the population to grow noticeable boobs even though they don’t need to be ‘swollen’ all the time, like other mammals.

Ps, I hope no one is offended by this question.