system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are breasts often considered sexually attractive and private?

Just a drunk thought...
gpt
Breasts are a sexual characteristic of human females. Other mammals only have breasts when breast feeding, otherwise they are small and look the same as the male breast of the species. 

Scientists are still trying to work out the specifics, but the attraction is thought to lay in something about youth (old people=less fertile=worse looking breasts), nutrition (need fat reserves to make nice ones) or simple weird sexual selection (think peacock's tail, not very useful but the ladies like them).

Unlike what many people say, breasts are sexualized across cultures, but the topless ethnic women we see have a different culture on what is considered "nude," not what is considered sexual.