And I would strongly suspect it’s because it has become enshrined in cultural norms and mores, as is the reprobation of women who subvert these norms (i.e. “sluts”). IME, girls who break that conditioning, say “fuck that noise” and take it upon themselves to initiate don’t do much less of it than if they were one of the lads.
They are also awesome, and I wish there were more of them 
I think you’re over-complicating something that has a very simple explanation:
Gay couples have twice the testosterone of a straight couple.
Lesbian couples have even less testosterone than a straight couple.
Sven, when FtM transsexual take testosterone, they almost invariably report a drastically increased sex drive.
It seems to me that women enjoy sex as much as men, maybe even more than men. When it’s, you know, done right. But that’s not the same thing as having the same drive as men.
AFAICT, this is the only data cited so far in this thread that shows clear evidence for a stronger male sex drive being (almost) indisputably linked to biological rather than cultural reasons.
It’s very hard to draw conclusions about male and female biological differences based only on behavioral differences, because behavior is conditioned by culture as well as biology. But if the same individual essentially experiences the sex drive both as a female and as a male and finds the male drive stronger, and if this holds true for most such individuals, that seems to pretty much settle the question.
(Of course, to be as accurate as possible we’d have to try to take into account psychological effects of the gender reassignment; maybe feeling better about the gender of one’s body increases sex drive. However, if MtF transsexuals find a corresponding decrease in libido when they stop having male bodies—and AFAICT it seems to be generally true that they do—then we can rule that out as a possible confounding factor.)
You can access the entire article here and it does go into significant depth on the multiple lines of evidence that all build towards the conclusion that men have stronger sex drives.
In terms of the science behind sex drive, there seems to be some evidence to suggest that men have a higher sex drive then women. A WebMD article by Richard Sine points to the idea that women are heavily influenced by society and their peers, and thus will garner their level of sexual desire from what is perceived to be “normal”.
How true this really is I don’t know, but as a student of gender history I can see how this conclusion has come about. Our concepts of gender and sex are little more than social constructs. In the 16th century for instance, women were perceived to be the lustful sex, with their desires threatening the status quo. Widows in particular were considered extremely dangerous, as the already “knew man” and often had a certain level of economic independence.
However, come the 18th century and the Evangelical Revival (in Britain at least) altered how women were represented, now portraying them as frail, passive, virginal creatures that were more “godly” than their male superiors in need of protection.
So, women’s perceptions of themselves have mostly likely altered alongside that of society’s, seeing as we are apparently predisposed to rely on the information of others to influence our attitudes to sex (and life more broadly).
Literary sources are particularly useful in tracking the changes in gender conceptualisation. Take, for instance, John Webster’s “The Duchess of Malfi”, that represents women as dangerous, lusty creatures that were likely to succumb to their desires with ease. Bram Stoker’s “Dracula” by contrast sees the character of Lucy Westenra being a pure, virginal, weak female in dire need of men’s assistance in all areas of her life (and death).
All these notions of gender roles feed into our conceptions of sexual desire. Having been constructed by influential institutions (I won’t name names…), they seep into our perceptions of ourselves and eventually become a cultural norm.
So, in conclusion, as far as I can gather there’s some biological evidence to suggest men are hornier than women, but it’s pretty likely that we’ve accepted the fact because its become the conventional idea in society.
Also, sorry for carrying on a bit, I just find this topic pretty interesting!
There’s a high risk of expectation-confirmation bias in this kind of research. When the definition of what constitutes “horniness” is largely driven by thinking of it as defined by and described by horny men, —— and I do believe that is the case —— then it’s likely that studies of the two sexes would indicate that, yeah, males manfest more of it.
Good point. For example, we tend to categorize “desire for short term pairings with a variety of partners” as “horny,” even though first encounters and flings tend to be pretty vanilla and repetitive in terms of what you are actually doing sexually. Not a lot of people bust out the anal double fisting with a hookup from the bar. With a few surprises, casual sex going to be mostly pretty straight forward sex, with the occasional blow job to mix things up.
On some other planet, we may consider plumbing the erotic depths with a longer term partner as representing “horny” more than multiple superficial encounters. We could easily say that “horny” people hold on to an affair while they push their sexual boundaries, while “less horny” people give it a few pumps with whoever is around and figure that is enough.
…which is why multiple measures are helpful. The measures in the linked article included, “spontaneous thoughts about sex, frequency and variety of sexual fantasies, desired frequency of intercourse, desired number of partners, masturbation, liking for various sexual practices, willingness to forego sex, initiating versus refusing sex, making sacrifices for sex, and other measures.”
The OP asked, “How much?” though. That’s more difficult to answer, given the variety of measures listed above.