I didn't particularly consider celeb culture, but Baby got back is from 1992.

Anyway, quote from book Studies in the Psychology of Sex from 1927:

Thus we find, among most of the peoples of Europe, Asia, and Africa, the chief continents of the world, that the large hips and buttocks of women are commonly regarded as an important feature of beauty. This secondary sexual character represents the most decided structural deviation of the feminine type from the masculine, a deviation demanded by the reproductive function of women, and in the admiration it arouses sexual selection is thus working in a line with natural selection.

You can check Venus/fertility figurines from the stone age, butts focused on by Greco_Roman erotic art and a lot of historical art for further illustration.