Nipple stimulation
For women, stimulation of the breast area during sexual intercourse or foreplay, or solely having the breasts fondled, can create mild to intense orgasms, sometimes referred to as a breast orgasm or nipple orgasm. Few women report experiencing orgasm from nipple stimulation. Before Komisaruk et al.s functional magnetic resonance (fMRI) research on nipple stimulation in 2011, reports of women achieving orgasm from nipple stimulation relied solely on anecdotal evidence. Komisaruks study was the first to map the female genitals onto the sensory portion of the brain; it indicates that sensation from the nipples travels to the same part of the brain as sensations from the vagina, clitoris and cervix, and that these reported orgasms are genital orgasms caused by nipple stimulation, and may be directly linked to the genital sensory cortex ("the genital area of the brain").An orgasm is believed to occur in part because of the hormone oxytocin, which is produced in the body during sexual excitement and arousal and labor. It has also been shown that oxytocin is produced when a man or womans nipples are stimulated and become erect. Komisaruk also relayed, however, that preliminary data suggests that nipple nerves may directly link up with the relevant parts of the brain without uterine mediation, acknowledging the men in his study who showed the same pattern of nipple stimulation activating genital brain regions.
The literature started with the argument that female orgasm is a byproduct of shared early male ontogeny, where male orgasm is an adaptation. Research has shifted to investigate and also support the sire-choice hypothesis, which proposes that female orgasm has been shaped by natural selection to function in the selection of high quality sires (male parents) for offspring. Therefore, orgasm increases the chances of conceiving with males of a high genetic quality. Research by Randy Thornhill et al. (1995) suggested that female orgasm is more frequent during intercourse with a male partner with low fluctuating asymmetry. Selective pressure and mating
Wallen K and Lloyd EA stated, "In men, orgasms are under strong selective pressure as orgasms are coupled with ejaculation and thus contribute to male reproductive success. By contrast, womens orgasms in intercourse are highly variable and are under little selective pressure as they are not a reproductive necessity. "Desmond Morris suggested in his 1967 popular-science book The Naked Ape that the female orgasm evolved to encourage physical intimacy with a male partner and help reinforce the pair bond. Morris suggested that the relative difficulty in achieving female orgasm, in comparison to the males, might be favorable in Darwinian evolution by leading the female to select mates who bear qualities like patience, care, imagination, and intelligence, as opposed to qualities like size and aggression, which pertain to mate selection in other primates. Such advantageous qualities thereby become accentuated within the species, driven by the differences between male and female orgasm.