User:SarahH04/sandbox

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Introduction
In order to encourage mating in non-conceptive periods and to encourage males to maintain their proximity, males must possess imperfect knowledge of the female’s fertility status, which is achieved in most animals that exhibit extended female sexuality through concealed ovulation. A review of relevant studies revealed that in humans, females only exhibit subtle changes during estrus, making it difficult for males to assess their fertility with precision. In the !Kung tribe, females lack any overt signals of fertility and are continuously receptive, encouraging males to remain continuously and provide resources.

Male Assistance Hypothesis
Mating outside the fertile window of their ovulatory cycle may incur considerable costs for females, such as in time and energy usage. To counteract these costs, the male assistance hypothesis argues that females exhibit this behaviour to obtain resources from males. The resources vary between species, but can include food, social alliance and protection of the female and her offspring. For example, in the Trobriand tribe, men give women gifts in exchange for sexual access. From this hypothesis, three predictions can be made.

Male provision of non-genetic resources
Firstly, in species that demonstrate extended female sexuality, there should be evidence that the males provide non-genetic resources to females. This prediction is supported in a variety of animals, with reviews revealing that male assistance is provided to certain mammals and communally breeding birds in exchange for mating outside the conceptive period.

Enhanced reproductive success
Secondly, in order to outweigh the aforementioned costs, mating in infertile phases of the ovulatory cycle should increase females’ reproductive success. Current research has only investigated this factor indirectly and predominantly in insects. For example, when male insects deliver material benefits in exchange for sexual access, the reproductive success of the females increases with the number of matings. It is important to note that the mating behaviour assessed was not limited to extended female sexuality. Hence it only provides indirect support for the second hypothesis.

Shifting mate preferences and behaviour across the ovulatory cycle
The final hypothesis has been extensively investigated. It predicts that females will exhibit differing mate preferences during fertile and non-fertile periods of their ovulatory cycle. Specifically, when fertile, the females will be sensitive to indicators of high genetic quality to increase the genetic quality of her offspring. Conversely, outside of the fertile period, females will show a preference for males who can provide resources for her and her offspring. In most species, males of higher genetic quality offer fewer non-genetic resources (such as shelter and food) than those of lower quality, so females are likely to choose different males at each stage.

Evidence for this hypothesis has been found in many different species. In hens, those near peak fertility show a preference for socially dominant roosters with large combs. Larger combs have been reliably associated with health and offspring survival so reliably indicate the genetic quality of the rooster. In the non-fertile phases, hens mate more indiscriminately with less regard for the larger comb size. A similar pattern emerges in humans. A review of relevant studies on female preferences across the ovulatory cycle reveals that women show a greater preference for masculine traits in fertile phases, especially for short term mating intention. This finding occurs across a variety of traits, such as masculine voices, body and facial features, scent and behavioural displays. The level of masculinity acts as an indicator of genetic quality through its association with high testosterone. Similarly, women show a preference for higher levels of symmetry, which is thought to indicate underlying developmental stability. However, during infertile phases, women prefer males with lower masculinity and symmetry as they tend to be more willing to offer material benefits.

In addition to impacting mating preferences, females have been found to exhibit differing mating behaviour at different cycle stages. An analysis of 121 studies with female birds showed that most mate outside their pair bond at a higher rate when fertile, especially when the primary partner possesses indicators of low quality genes. During infertile phases, birds showed reductions in this behaviour, suggesting that the function of extended female sexuality is not to increase the genetic quality of offspring. In humans, females show increased motivation for mating with other males at mid-cycle without an accompanying increase in copulation with their long term partner, especially if the partner is of lesser physical attractiveness.