Pheromones and the battle of the sexes--论文代写范文精选

女性排卵期有明显的生理和行为变化,嗅觉感知是一种无意识机制，与生理和行为相关联，改变月经周期。女性生育能力仍将连着亲子血缘。下面的essay代写范文进行详述。

Abstract 
Parental investment theory [65] predicts that females who look for long-term relationships should seek out and choose males who are ready to invest resources in their offspring. This minimizes female investment, but maximizes overall investment through added male assistance. In contrast, males are expected either to attempt copulation frequently with as many fertile females as possible, or to develop a pair bond. This helps to ensure that either a large number of offspring survive without signifi cant paternal investment, or that paternal investment occurs primarily when another male does not father offspring. According to this theory, it is adaptive for females and males to develop and use cognition in mate selection, which takes into account biological constraints. 

Thus, mate selection is a task of information processing, and evolution would favor individuals who were able to quickly and reliably process information that allowed them to make appropriate mating decisions. Adaptive cognition could be expected to lead to optimal decision-making under a wide spectrum of socioeconomic constraints. The existence of ubiquitarian sex specifi c differences in mate selection criteria [72] attests that male and female cognition is adapted to the biological constraints of mate selection. For example, neither males nor females consciously perceive human ovulation. 

Since ovulation is associated with a number of overt physiological and behavioral changes, it is surprising that it is not consciously detected. However, olfactory perception is one “unconscious” mechanism that is associated both with the physiological and behavioral changes of the menstrual cycle. Alexander and Noonan [73] and also Symons [74] have argued that concealed ovulation evolved because females need to trick males into forming a bond. Males who were not aware of optimal (i.e., ovulatory) female fertility would remain bonded to ensure impregnation and paternity. A female who provided cues to ovulation might risk losing paternal investment, due to paternal uncertainty and limited temporal reproductive interaction. This hypothesis implicates male fear of cuckoldry as an evolutionary pressure [65]. 

One evolutionary outcome would be that the female‘s ability to secure paternal care is affected by mechanisms that increase temporal aspects of the pair bond and enhance male confi dence of paternity. Concealed ovulation is a mechanism that fi ts this hypothesis. In contrast, Benshoff and Thornhill [75] as well as Symons [74] have proposed an alternative evolutionary scenario where concealed ovulation evolved to increase the chances of successful cuckoldry by females so they “can escape the negative consequences of being pawns in marriage games” [76]. Once monogamy is established, a female’s best strategy would be to copulate outside the pair bond because she could then obtain superior genes with a certain expectation of paternal investment, and the increased survival of genetically superior offspring. These two hypotheses imply different impacts of heritable traits. 

If genes, which induce paternal care, were relevant for offspring success, a male paternitysecuring function for concealed ovulation would be possible. If there were other traits not related to paternal care but relevant to offspring survival, then concealed ovulation would allow females to exploit occasional opportunities to mate outside the pair bond [77]. In both cases, overt cues of ovulation may be selected against because it would hinder the female’s mating strategies [73, 78]. The second hypothesis has received considerable support from Bellis and Baker [79]. They conducted a study of 2708 females and found those 13.8% of 145 “unprotected” extra-pair copulations (EPC) occurred during the ovulatory phase of the menstrual cycle and were preceded in most cases by intra-pair copulations (IPC). EPCs were rarely followed by IPCs. 

According to his study EPCs, and thus, female infi - delity peak at ovulation. The authors conclude that these results hint at female-induced sperm competition, which would be expected by the second hypothesis of the evolutionary function of concealed ovulation discussed above. It is still unclear what proximate mechanism or mechanisms cue female EPC at ovulation. The possibility has been raised [80] that conditioning might facilitate response to sexual stimulation should it fi rst be encountered during the follicular phase. In this regard, pheromonal stimuli from a male, fi rst encountered during ovulatory sexual intercourse, might help to neuroendocrinologically condition a female’s sexual response. 

Similarly, pheromonal stimuli from a female, fi rst encountered during ovulatory sexual intercourse, might help to neuroendocrinologically condition a male’s sexual response, and help to ensure properly timed reproductive sexual behavior [81]. In any case, the assumption that concealed ovulation serves to deceive males is common to all these theories. Supposedly, females deceive males about the fertile phase of the menstrual cycle to help ensure male parental investment, which yields an optimal number of offspring. Additionally, concealed ovulation helps females to monopolize reproduction, and – as a consequence - forces males to develop reproductive strategies for gaining access to ovulating females. It is reasonable to expect male counter strategies would develop against deceptive attempts by females to conceal ovulation. Grammer [82] described a possible male counter strategy: the evolution of the androstenone-androstenol signaling system. 

In a study, 290 female subjects rated the odor of androstenone. A change in assessment throughout the menstrual cycle was found: ovulatory women found the scent of androstenone, the most dominant odor of the male armpit, to be more pleasant than on the other days of the menstrual cycle. These results suggest that there is a change in the emotional evaluation of males triggered by the reaction to androstenone. The fi ndings support previous results by Maiworm [64], which were of borderline signifi cance. Male body odor is usually perceived as unattractive and unpleasant by females but this evaluation changes when conception is most likely, and androstenone, minimally, becomes less aversive. This fi nding is underlined by the fact that anosmia to androstenone also varies with cycle. With optimal likelihood of conception, we fi nd fewer anosmic females [82]. 

It seems possible that changes in the ability to perceive musky male odors during the menstrual cycle could also be a female strategy, although more data need to be gathered to support this hypothesis. However, the change in female attitude towards male body odor can be expected to impact mate selection and perhaps self-initiated copulations by females. With regard to the androstenol-androstenone signaling system, the situation for androstenol seems clear – it makes males more attractive to females. 

But females are less likely to act on this olfactory-based attraction unless fi tter males produce more androstenol. The situation is more complicated because producing androstenol inevitably produces androstenone. The androstenone production has a disadvantage because of its unpleasantness. Attractiveness-enhancing androstenol immediately oxidizes to androstenone, which repels females. A non-producing male could do quite well in a population of producers, because females would not be repelled by his body odor. Thus the attractiveness-enhancing component of the smell does not seem to be the main, or at least only, function of the signaling system. Regarding androstenone, the fact that ovulatory females assess its odor as more pleasant could be advantageous for males, as odorous males would be more suc cessful when approaching ovulating females, rather than non-ovulating females. This suggests that males use a kind of passive “ovulation-radar” for the detection of concealed ovulation. 

The concept of ovulation radar fi ts our hypotheses about affective reactions. For example, a pheromone from the male elicits change in the hormonal milieu of the female. However, the female is not aware of this change, even though the hormonal change affects her behavior. Similarly, pheromones from the female elicit changes in the hormonal milieu of the male that affect his behavior by chemically signaling him that the female is ovulating. Females faced with an evolved male strategy to detect concealed ovulation would be likely to develop a counter strategy. One possible strategy could be to manipulate male cognition and thus adaptive male information processing in mate selection. Other mammalian males, including non-human primates (especially rhesus monkeys) perceive both estrogen-related reproductive fi tness and ovulation through olfaction. Although normally motivated to copulate, when sexually inexperienced rhesus males were made anosmic, they showed no further sexual motivation, despite a powerful visual cue: the female’s swelling [83]. 

Furthermore, rhesus males show no interest in ovariectomized rhesus females, presumably because ovariectomized rhesus females lose the odor characteristic of higher estrogen levels at ovulation. Rhesus males regain interest in copulation when the vaginal secretions from intact (e.g., estrogenized) females are applied to ovariectomized females. Studies on menstrual cycle fl uctuations in the fatty-acid composition of women’s vaginal fl uids indicated that a similar type of estrogen-based chemical signaling system might also exist in humans [84, 85, 86, 87]. For example, human vaginal secretions have a composition that is similar to the vaginal secretions of female rhesus monkeys. 

The application to ovariectomized female rhesus monkeys, either of human, or rhesus vaginal secretions, induced similar activation of rhesus male sexual interest [88]. The behaviorally active fraction of the rhesus vaginal secretions - referred to as “copulins” - consists of volatile, short-chained fatty acids [89]. These same substances (i.e., the short-chained fatty acids: acetic-, propanoic-, butanoic, methylpropanoic-, methylbutanoic-, methylpentanoic acid) occur in human vaginal secretions, albeit in slightly different amounts [85]. In addition, the composition of these copulins varies during the menstrual cycle. Preti and Huggins [86] confi rmed this observation. Cowley, Johnson, and Brooksbank [90] found that rhesus vaginal secretions change peoples’ assessment of other people, and that the application of copulins tends to yield a more positive impression of females. Doty, Ford, and Preti [91] used a questionnaire to evaluate the intensity and pleasantness of different vaginal fl uids from a complete menstrual cycle. They found that odor at ovulation was both the most intense odor, and the least unpleasant odor. Juette [43] synthesized female vaginal secretions (“copulins”) and tested for their ability to act as chemical signals for males. 

Menstrual, ovulatory and pre-menstrual fatty acid compositions of copulins and an odorless water control were presented to 60 nonsmoking male subjects for 25 minutes in a double-blind experiment. To control for changes in sex hormones that were induced by copulins, saliva-samples were taken before and after presentation. While inhaling, either a composition of copulins or a control, males rated pictures of females for attractiveness. Ovulatory fatty acid compositions stimulated male androgen secretion and changed the discriminatory cognitive capacities of males with regard to female attractiveness. Males became less discriminating. Therefore the copulins may act as putative human pheromones and provide beautifully balanced “strategic weapons“ in the “battle of the sexes” and the “war of signals” resulting from sex differences in parental investment theory. However, it is not necessary to view these “battles” or “wars” only from the perspective of parental investment theory. Mammalian pheromones ensure properly timed reproductive sexual behavior in many species. 

It should surprise no one that pheromones would be involved in properly timed human reproductive sexual behavior. If one examines what is known about the interaction between pheromones and our neuroendocrine system, there is support for the extension of mammalian olfactory communication to human behavior. First and foremost is the effect of mammalian pheromones on conspecifi cs of the opposite sex: the LH increase and reported ovulatory increase in male T, for example. Persky, Lief, O‘Brien, Straus, and Miller [92] commented on the observed ovulatory increase in T levels of human males, and suggested that, somehow, the female was signaling the male that she had ovulated, and that he responded, like a male rhesus monkey with an increase in T. Morris, Udry, Khan-Dawood, & Dawood [93] replicated this work and described their fi ndings as an unobserved event that causes increased intercourse. 

Though neither of these studies specifi cally mentioned human pheromones, affective reactions were present both in the male and in the female, and pheromones are the most likely cause of the affective reactions. For example, the increased T in the male can readily be linked to increased intercourse, whether or not the increased T was an observable event. Finally, Singh & Bronstad [81] showed that human males fi nd the natural body odor of ovulatory females to be most pleasant, when compared to the natural body odor during other phases of the menstrual cycle. The male’s hedonic rating of pleasant ovulatory odor; the increased T, and the increased intercourse, collectively offer signifi cant support for the concept that chemical communication is more important to properly timed reproductive sexual behavior than is visual or other sensory input. If, for example, male canines were able to tell us that they preferred the scent of estrus odor, and estrus odor increased male T, we would readily explain the affective reaction of the “bitch in heat” which correlates with increased copulation. 

Because sexual activity is not limited to the ovulatory phase of the menstrual cycle, human sexual behavior is considered to be more complex than that of other mammals who depend upon properly timed reproductive sexual behavior for species survival. There are other cues, besides chemical cues, that are involved. However, it is remarkable that many people consider visual cues to be more important than olfactory cues, when consideration is given for the mammalian mechanisms that ensure properly timed human reproductive sexual behavior.

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