Are a difficult thing to judge.
And they're a different thing to have.
This certainly gives me pause for thought by comparing all the girlfriends I've had in this life (both married and unmarried).

I think there have been studies that certain bone stuctures, beauty and/or handsomeness, femininity/masculinity are great indicators for libido (but not always). Natural selection and all that.
Even ugly girls can be promiscuous. But the libido is there, often driven by hormones. I know mine drove me for years. Sex is not appealing without the chemistry, so that great unknown enters the equation and the learning comes later.

Women process information differently than men. And I think we find men like our fathers. I think that's instinctively true.
(Wish I would have figured that out earlier.)