User:Psunco/sandbox

Male-Driven Hypothesis
An alternative explanation for female extended sexuality is the 'Male-driven hypothesis'. The theoretical basis of this hypothesis is based on male uncertainty regarding the fertility status of females. Although some physiological changes occur during the fertile period that may act as reliable indicators (e.g. the concentration of oestrogen can change female scent), most species have not evolved signals advertising fertility (e.g. sexual swellings). Therefore males will be unable to detect fertility with any precision. As a result, female extended sexuality is proposed as a male sexually selected trait. Males will pursue sexual access throughout the entirety of the ovulatory cycle to increase their chances of impregnating the female. According to this hypothesis, females lack any benefit from this activity due to their inability to conceive, yet will be coerced by males to engage in sexual intercourse.

The Training Hypothesis

Another hypothesis claiming that extended female sexuality has evolved to benefit males' interests is the 'training hypothesis'. It has been shown that women's immune systems attack foreign antigens found in sperm. This may reduce the likelihood of conception so reduce the reproductive success for the males. However, prior exposure to sperm antigens can dampen the immune response to increase the chances of successful conception and implantation. Therefore, males may have evolved to train and "condition" women's immune systems by copulating with females during infertile periods, in order to reduce the likelihood of her immune system reacting against the sperm's antigens from lack of exposure. Indeed, this hypothesis is supported by the work of Robertson et al. (2003). They found that couples who used condoms before trying to conceive were more likely to suffer complications, such as pre-eclampsia, during pregnancy as a result of the woman's immune system having no prior exposure to the antigens in the sperm.

This hypothesis has received much criticism. For example, as all mammals experience the same limitations to reproductive success from immune system responses to sperm antigens, this hypothesis predicts that all mammals should exhibit extended female sexuality. However, only few species of mammals exhibit sexual behaviour outside the conceptive period.

Spuhler's Hypothesis
Spuhler's hypothesis suggests that extended female sexuality has evolved as a by-product of an adaptation in females that increases the levels of adrenal hormones. He proposed that secretion of higher levels of adrenal hormones were initially selected in women in order to increase endurance for walking or running. This hypothesis suggests that the larger adrenal glands may have contributed to the development of extended female sexuality as they are also the main source of 'libido hormones', which increase the female's sexual drive. Thus, extended sexuality is little to do with sexual behavior, or evolutionary advantage, but rather it is just a by-product of hormones. However, this hypothesis cannot account for female extended sexuality in invertebrates, which lack adrenal systems. Additionally Spuhler highlighted the existence of larger thyroid and adrenal glands in humans compared to other primates. However, no empirical evidence has established the link between hormones and endurance walking as an adaptation and female extended sexuality as a natural incidental effect. As there are costs to extended sexuality, it can be argued that selection would serve the dissociation of extended sexuality from the mechanism that affects endurance walking.

Spuhler's hypothesis might need to go as a separate section as I don't believe it is related to male driven benefits SarahH04 (talk) 17:16, 4 March 2016 (UTC)