When and for what function might female orgasm have originated in evolution?

What is it about?

Whereas male orgasm coincides with ejaculation and has a clear reproductive function in sperm transfer, the orgasm in females is not required for reproduction. What is more, female orgasm during reproductive sex is in fact surprisingly rare. This throws doubts on it having a direct reproductive function. Did it nevertheless evolve for some function, and did the function get lost, or changed, in evolution? In this paper we suggest that the human female orgasm is a remnant from the ancestral neuro-endocrine reflex which induces ovaries to release an egg (ovulation). Some species still have such copulation-induced ovulation, like rabbits, or cats. Other species, like humans, have evolved spontaneous ovulation which requires no external induction, however the reflex at coitus appears to have been maintained, even if it does not induce the ovulation anymore. Several strong lines of comparative evidence are provided for this explanation.

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Why is it important?

This work puts a female sexual trait in an evolutionary perspective. What is more, it provides an explanation, why the female orgasm is relatively rare during reproductive intercourse. The lack of female orgasm has long been seen as (mental) disorder. We have shown however that the same groups of species which ovulate spontaneously, have also changed female genital anatomy, positioning the clitoris outside of the copulatory tract.This reduces the direct stimulation during intercourse and naturally reduces the frequency of female orgasm during reproductive sex, requiring additional stimulation.

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