The sex drive refers to the strength of sexual motivation. Across many different studies and measures, men have been shown to have more frequent and more intense sexual desires than women, as reflected in 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. No contrary findings (indicating stronger sexual motivation among women) were found.Hence we conclude that the male sex drive is stronger than the female sex drive. The gender difference in sex drive should not be generalized to other constructs such as sexual or orgasmic capacity, enjoyment of sex, or extrinsically motivated sex
[...] Our review of the literature indicated that role of androgens (e.g., testosterone) was crucial in producing sex drive. We focused on the androgens for several reasons. First, scientists’ interest in the effects of testosterone have yielded a wealth of data on its effects. Second, testosterone is one of the primary organizational and activational hormones that differentiates men and women. Although both women and men have natural supplies of testosterone in their bloodstream, the amount of testosterone varies significantly between the genders. On average, men’s blood testosterone levels are 1,000 nanograms per deciliter, whereas women’s blood testosterone levels are only one seventh or one eighth of this amount (see Dabbs, 2000; Mazur & Booth, 1998). Postmenopausal women have especially low levels of testosterone (regardless of whether menopause occurs naturally or as a result of surgical procedures). Most commonly, surgically induced menopause is the result of an oophorectomy (i.e., removal of the ovaries and adrenals) or hysterectomy (i.e., removal of the uterus). Third and perhaps most germane to this analysis, evidence from the animal and human literatures suggests that androgens are responsible for active initiation of sexual activity (i.e., proceptivity), whereas estrogens are responsible for passive acceptance of sexual activity (i.e., receptivity; Beach, 1976; De Jonge & Van de Poll, 1984; Sherwin, 1988).
There are tons of studies cited over at "Alles Evolution" and it is well worth the read (even for people who don't know German).