Written by Emily Nagoski, Ph.D.
With regard to genitals, I'm talking about biological homology, something I've talked about a couple of times. With regard to function I'm mostly talking about the central nervous system, specifically the dual control model, the only theory of sexual response I know of that describes the actual MECHANISM underlying desire and arousal, rather than merely describing behavior or experience.
The short version:
The sexual response mechanism is made up of two parts: a gas pedal (sexual excitation system, or SES) and a brakes pedal (sexual inhibition system, or SIS). "Inhibition" here doesn't mean shy or prudish, it just means "off switch" versus SES's "on switch." All the time you've got signals going from your brain down to your spine to your genitals saying, "on!" and "off!" in response to sexually relevant information in the environment or threats, respectively.
Men's and women's sexualities are both made up of these two components. Alike.
What constitutes "sexually relevant information" or "threat" appears
to be almost entirely LEARNED, not innate, for both men and women.
Another thing they have in common. What this means is that it seems
there is no INHERENTLY arousing stimulus, that even a newborn infant
will respond to. (And yes, newborn infants are definitely capable of
arousal and even orgasm, although there's evidence of orgasm in utero.)
So everything that turns you on or turns you off is a product of a
lifetime of learning, NOT anything innate.
Both men's and women's sexualities are linked to their attachment systems, though possibly in different ways, as mediated by, among other things, the oxytocin receptor system. This is one example to illustrate how sex for humans, all humans, is not merely reproductive but SOCIAL.
And there's all the biological stuff: both produce gametes, both have a reproductive lifespan and lifecycle, much of the physiology is the same (increased bloodflow to genitals, myotonia, carpopedal spasms, tachycardia and increased blood pressure and respiration rate, etc., etc.) Famously, when people write down descriptions of their experiences of orgasm without referring to specific body parts, it's impossible to tell which experiences are men's and which are women's.
A there's some bigger stuff that *I* believe they have in common that are more cultural: both men and women are independent sexual agents with the right to ask for, consent to, or deny consent to sex; both men's and women's sexualities function not only for reproduction per se but for social functions: bonding, attachment, establishing dominance hierarchies, sharing resources, resolving conflict, and all the rest of it. And both men's and women's sexualities develop as a consequence of the dynamic interaction of biology and experience: almost nothing is purely innate in either.