GEN1499 Although not expressed explicitly in the Torah, the Rabbis understood that, according to [this verse], Potiphar bought the Hebrew, Joseph, specifically for homosexual purposes.  Sotah 13b.  This is significant, as it clearly implies that homosexuality was prevalent in Egypt at that time.  Thus, when the Torah (later on) commands Jews not to imitate the ways of the Egyptians (and Canaanites), this prohibition could also include the practice of homosexuality that was commonly found in these societies.   This in fact is the Rabbinical source prohibiting lesbianism.   [See also 6:12 AMJV 140] AMJV 140