Proof that the penis is a much later development than the female vulva is found in the evidence that the male himself was a late mutation from an original female creature. For man is but an imperfect female. Geneticists and physiologists tell us that the Y chromosome that produces males is a deformed and broken X chromosome — the female chromosome. All women have two X chromosomes, while the male has one X derived from his mother and one Y from his father. It seems very logical that this small and twisted Y chromosome is a genetic error — an accident of nature, and that originally there was only one sex — the female.
The First Sex, ch. 1 - Woman and the Second Sex (1971).