^^^ This was based on Jack's statement in the show, and it's also been pointed out that Jack isn't that great of a doctor, either.
However, assuming that Jack does know how to determine the gender of skeletal remains (pelvic shape & brow ridge differences), here's my theory: As most mythology is to believed to derive from some nugget of reality, I suspect that "Adam and Eve" on the island are the two real people whom the mythological Egyptian gods "
Anubis" and "
Tawaret" are based on, as evidenced by the wall carvings in the temple and statue showing both of these opposing deities -
Anubis, god of the underworld/afterlife/mummification/death and
Tawaret, the god
dess of fertility and child birth.