两
性之间产生吸引力的重要因素是化学物质。最近的研究表明，如果女性服用激素避孕，如口服避孕药，就会破坏女性身上传出的化学信号，影响她们对男性的吸引力和这些女性自己对爱侣的偏好。
Everett Collection
正在参加舞会的男女们。排卵期内的女性青睐面部对称性强、男性特征更为突出的男性，这些性特征包括肌肉力量、更为男性化的嗓音和支配行为。
研究进化的心理学家和生物学家很早就对人们选择爱侣的因素发生了兴趣。上个世纪九十年代进行了一项有影响的研究，这项研究被人们称为“T恤衫研究”。研究人员请一些女性嗅闻一些男子穿过的T恤衫之后，分别说出这些异性对她们的吸引力。研究结果发现，和很多动物一样，人类可以也可以通过被称之为“外激素”的化学气味来传达和识别性吸引资讯。
这项研究还表明，女性似乎更青睐那些免疫系统与其自身的免疫系统基因（被称为“MHC”）差异最大的男性。基因家族能够让人体识别出哪些细菌是外来入侵者，并且能够保护人体不受这些细菌的感染。科学家认为，从进化的角度来看，如果父母的MHC基因存在差异，那么他们的后代就能免受更多病原体的侵害，从而更为健康。
资料追踪程式显示，在去年一年里，美国医生一共开出了逾9200万个激素避孕处方，包括口服药片、避孕贴和注射剂。
研究人员说，他们的目的不是恐吓或阻止女性采取激素避孕措施。英国伦敦大学学院（University College London）的研究人员亚历山卓•阿尔韦涅（Alexandra Alvergne）说，我们只是想知道，在服用避孕药的时候，我们到底是在做什么。如果这种行为有可能危及我们的浪漫生活和孩子的健康，我们需要加以了解。 阿尔韦涅博士去年在期刊《生态和进化趋势》（Trends in Ecology and Evolution）上发表了一篇评论文章，详细列出了目前有关这个课题的所有文献。
研究显示，在女性排卵期间，也就是她容易受孕的期间，男性和女性对对方的偏好都会发生改变。一些研究追踪了女性对不同男性照片的反应，另一些研究则在几周的时间里询问女性对男性的感觉。结论之一是，排卵期内的女性青睐面部对称性强、男性特征更为突出的男性，这些性特征包括肌肉力量、更为男性化的嗓音和支配行为。女性还似乎尤其欣赏MHC基因的差异性。从进化的角度来看，这些特征表明男性拥有更强的生殖力，也有更优良的基因可以传给后代。
排卵期的女性往往会展现出一些微妙的暗示。男性往往会觉得这个时候的她们更漂亮。加州大学洛杉矶分校的沟通与心理学教授马特尔•哈兹尔顿（Martie Haselton）说，这时候，女性就会竭力展现自己的迷人之处，比如通过穿紧身衣或更为暴露的衣服。这方面的研究包括向几组鉴定人展示女性在一个月内换穿的所有服装的照片。这个时期的女性还会释放化学信号，告诉男性她们处于易受孕期；哈兹尔顿博士说，研究人员测量了这个时期的女性的各种体味。哈兹尔顿博士在期刊《最新心理科学指南》（Current Directions in Psychological Science）上发表了一篇文章，论述男性察觉处于排卵期的女性的能力。
研究显示，当女性采用激素避孕时，这种自然偏好就会被完全破坏。在口服避孕药期间，处于排卵期内的女性不再渴望传统上那种性特征突出的男性。对与自己免疫性有差异的男性的偏好也会消失。科学家说，可能是因为传递排卵期信号的暗示已经不复存在，所以在女性的整个月经周期内，男性对她们的兴趣也就不会发生强弱变化。
长期以来，一些使用口服避孕药的女性反应说，这些药物能改变她们的性欲和心情。服用激素避孕药对女性选择爱侣和忠实于对方有什么影响，这一研究目前尚处于初级阶段。研究人员推断，停止避孕之后，如果爱侣的男性特征较弱，女性可能会降低对对方的兴趣，导致二人之间关系出现罅隙。并且，如果避孕措施会影响女性发觉基因差异的本能，那么，男女相恋时女方正好服用避孕药的话，两人的孩子在基因健康方面可能出现问题。
阿尔韦涅博士说，目前的研究还不足以得出肯定的结论，但是可以肯定的是，如果女性对男性特征[的渴望]不经历一点“提升”，那她最终就很可能选择男性特征不够理想的爱侣。
研究表明，这可能促使一些女性红杏出墙。2010年，新墨西哥大学（University of New Mexico）心理学家史蒂芬•甘杰斯特（Steven Gangestad）和他的研究团队发布的一份研究报告称，他们调查了60对夫妇之后发现，在易受孕期内，爱侣的男性特征不够理想的女性对其他男性会更具吸引力，而与传统上男性特征明显的伴侣结合的女性则不会产生这种冲动。
在另一项研究中，研究人员对48对夫妇的MHC基因样本进行了分析。结果发现，伴侣之间的基因差异越小，女性对伴侣的性要求回应就越差。
越来越多的证据表明，在女性采取避孕措施时，男性的反应有所不同。2004年，期刊《行为生态学》（Behavioral Ecology）刊载的一项研究中也采用了“T恤衫研究”的方法，但是这些T恤衫是女性穿着的。评判小组中的31位男性嗅闻了提供的所有的T恤衫之后，认为没有服用避孕药、正在排卵期的女性穿过的T恤衫对他们的吸引力最大。评判小组中12位女性没有发现T恤衫味道的不同。
一项针对灵长类动物的研究也支持激素避孕影响择偶偏好这一说法。杜克大学（Duke University）的研究人员研究了一些雌性狐猴在接受激素避孕前后分泌的荷尔蒙，并研究了雄性狐猴对这些气味的偏好。
今年的《皇家学会会报：生物科学》(Proceedings of the Royal Society, Biological Sciences)公布了上述研究成果，其中显示，注射甲羟孕酮避孕针（一种获准用于人体注射的长效避孕针剂）可以极大地改变雌性狐猴释放的化学物质，而这些物质能够显示它们的个性特征和基因健康情况。
杜克大学进化人类学专业的教授兼本项研究的资深作者克莉丝蒂娜•德雷（Christine Drea）说，相比注射前，注射避孕药物之后的雌性狐猴对雄性狐猴的性吸引大为降低。她说，避孕药物消除了正常的气味信号所传递的资讯。
德雷教授说，虽然要想获得直接的结论，还需要针对人类进行研究，但是人类与动物之间可能存在相似之处。避孕药物“可以弄乱你[身上发出的信号]，让别人嗅闻不出真实的你，”她说。
Shirley S. Wang
（本文版权归道琼斯公司所有，未经许可不得翻译或转载。）
Much of the attraction between the sexes is chemistry. New studies suggest that when women use hormonal contraceptives, such as birth-control pills, it disrupts some of these chemical signals, affecting their attractiveness to men and women's own preferences for romantic partners.
The type of man a woman is drawn to is known to change during her monthly cycle -- when a woman is fertile, for instance, she might look for a man with more masculine features. Taking the pill or another type of hormonal contraceptive upends this natural dynamic, making less-masculine men seem more attractive, according to a small but growing body of evidence. The findings have led researchers to wonder about the implications for partner choice, relationship quality and even the health of the children produced by these partnerships.
Evolutionary psychologists and biologists have long been interested in factors that lead to people's choice of mates. One influential study in the 1990s, dubbed the T-shirt study, asked women about their attraction to members of the opposite sex by smelling the men's T-shirts. The findings showed that humans, like many other animals, transmit and recognize information pertinent to sexual attraction through chemical odors known as pheromones.
The study also showed that women seemed to prefer the scents of men whose immune systems were most different from the women's own immune-system genes known as MHC. The family of genes permit a person's body to recognize which bacteria are foreign invaders and to provide protection from those bugs. Evolutionarily, scientists believe, children should be healthier if their parents' MHC genes vary, because the offspring will be protected from more pathogens.
More than 92 million prescriptions for hormonal contraceptives, including pills, patches and injections, were filled last year in the U.S., according to data-tracker IMS Health.
Researchers say their aim isn't to scare or stop women from taking hormonal contraceptives. 'We just want to know what we're doing' by taking the pill, says Alexandra Alvergne, a researcher in biological anthropology at University College London in the U.K. 'If there is a risk it affects our romantic life and the health status of our children, we want to know.' Dr. Alvergne last year published a review detailing the existing literature on the topic in the journal Trends in Ecology and Evolution.
Both men's and women's preferences in mates shift when a woman is ovulating, the period when she is fertile, research has shown. Some studies have tracked women's responses to photos of different men, while other studies have interviewed women about their feelings for men over several weeks. Among the conclusions: When women are ovulating, they tend to be drawn to men with greater facial symmetry and more signals of masculinity, such as muscle tone, a more masculine voice and dominant behaviors. The women also seemed to be particularly attuned to MHC-gene diversity. From an evolutionary perspective, these signals are supposed to indicate that men are more fertile and have better genes to confer to offspring.
Women tend to exhibit subtle cues when they are ovulating, and men tend to find them more attractive at this time. Women try to look more attractive, perhaps by wearing tighter or more revealing clothing, says Martie Haselton, a communications and psychology professor at the University of California, Los Angeles. Research on this includes studies in which photos that showed women's clothing choices at different times of the month were shown to groups of judges. Women also emit chemical signals that they are fertile; researchers have measured various body odors, says Dr. Haselton, who has a paper on men's ability to detect ovulation coming out in the journal Current Directions in Psychological Science.
Such natural preferences get wiped out when the woman is on hormonal birth control, research has shown. Women on the pill no longer experience a greater desire for traditionally masculine men during ovulation. Their preference for partners who carry different immunities than they do also disappears. And men no longer exhibit shifting interest for women based on their menstrual cycle, perhaps because those cues signaling ovulation are no longer present, scientists say.
Some women using birth-control pills have long reported changes to their libido and mood. Research is still in the early stages to explore the implications of taking hormonal contraceptives for women's choice of mates and for fidelity in relationships. Researchers speculate that women with less-masculine partners may become less interested in their partner when they come off birth control, contributing to relationship dissatisfaction. And, if contraceptives are masking women's natural ability to detect genetic diversity, then the children produced by parents who met when the woman was on the pill may be less genetically healthy, they suggest.
'We don't have enough research to draw a firm conclusion yet,' says Dr. Haselton. 'It is certainly possible that if women don't experience that little uptick in [desiring] masculinity that they end up choosing less masculine partners,' she says.
That could prompt some women to stray, research suggests. Psychologist Steven Gangestad and his team at the University of New Mexico showed in a 2010 study that women with less-masculine partners reported an increased attraction for other men during their fertile phase. Women partnered with traditionally masculine partners didn't have such urges, according to the study of 60 couples.
In another study, the researchers analyzed MHC gene samples of 48 couples. Women partnered with men with whom they shared the least genetic diversity reported being less sexually responsive to their mates. The study was published in 2006 in the journal Psychological Science.
There is also accumulating evidence indicating men react differently to women when they are on birth control. A 2004 study in the journal in Behavioral Ecology used the T-shirt study methodology but instead put the shirts on 81 women. A panel of 31 men, smelling the T-shirts, experienced the greatest attraction for the non-pill-using women when they were ovulating. Twelve women on the panel didn't detect any difference.
A study on primates appears to support the idea that hormonal contraceptives change mating preferences. Duke University researchers studied hormones secreted by female lemurs before and after the animals received a hormonal contraceptive. They also studied males' preferences for these scents.
The findings, published in the journal Proceedings of the Royal Society, Biological Sciences this year, showed that the injection of Depo-Prevara, a long-lasting contraceptive that is approved for use in humans, dramatically altered the chemicals that female lemurs give off to indicate their identity and how genetically healthy they are.
The females given the contraceptive became overall less appealing to the males than before getting the injection, says Christine Drea, a professor in Duke's evolutionary anthropology department and senior author on the study. The contraceptive erased all the normal information the odor signals conveyed, she says.
Though the study would need to be conducted in humans to draw direct conclusions, there are potential parallels to people, Dr. Drea says. Birth control 'could be mixing up your own [signals] and others aren't smelling the real you,' she says.
Shirley S. Wang
The type of man a woman is drawn to is known to change during her monthly cycle -- when a woman is fertile, for instance, she might look for a man with more masculine features. Taking the pill or another type of hormonal contraceptive upends this natural dynamic, making less-masculine men seem more attractive, according to a small but growing body of evidence. The findings have led researchers to wonder about the implications for partner choice, relationship quality and even the health of the children produced by these partnerships.
Evolutionary psychologists and biologists have long been interested in factors that lead to people's choice of mates. One influential study in the 1990s, dubbed the T-shirt study, asked women about their attraction to members of the opposite sex by smelling the men's T-shirts. The findings showed that humans, like many other animals, transmit and recognize information pertinent to sexual attraction through chemical odors known as pheromones.
The study also showed that women seemed to prefer the scents of men whose immune systems were most different from the women's own immune-system genes known as MHC. The family of genes permit a person's body to recognize which bacteria are foreign invaders and to provide protection from those bugs. Evolutionarily, scientists believe, children should be healthier if their parents' MHC genes vary, because the offspring will be protected from more pathogens.
More than 92 million prescriptions for hormonal contraceptives, including pills, patches and injections, were filled last year in the U.S., according to data-tracker IMS Health.
Researchers say their aim isn't to scare or stop women from taking hormonal contraceptives. 'We just want to know what we're doing' by taking the pill, says Alexandra Alvergne, a researcher in biological anthropology at University College London in the U.K. 'If there is a risk it affects our romantic life and the health status of our children, we want to know.' Dr. Alvergne last year published a review detailing the existing literature on the topic in the journal Trends in Ecology and Evolution.
Both men's and women's preferences in mates shift when a woman is ovulating, the period when she is fertile, research has shown. Some studies have tracked women's responses to photos of different men, while other studies have interviewed women about their feelings for men over several weeks. Among the conclusions: When women are ovulating, they tend to be drawn to men with greater facial symmetry and more signals of masculinity, such as muscle tone, a more masculine voice and dominant behaviors. The women also seemed to be particularly attuned to MHC-gene diversity. From an evolutionary perspective, these signals are supposed to indicate that men are more fertile and have better genes to confer to offspring.
Women tend to exhibit subtle cues when they are ovulating, and men tend to find them more attractive at this time. Women try to look more attractive, perhaps by wearing tighter or more revealing clothing, says Martie Haselton, a communications and psychology professor at the University of California, Los Angeles. Research on this includes studies in which photos that showed women's clothing choices at different times of the month were shown to groups of judges. Women also emit chemical signals that they are fertile; researchers have measured various body odors, says Dr. Haselton, who has a paper on men's ability to detect ovulation coming out in the journal Current Directions in Psychological Science.
Such natural preferences get wiped out when the woman is on hormonal birth control, research has shown. Women on the pill no longer experience a greater desire for traditionally masculine men during ovulation. Their preference for partners who carry different immunities than they do also disappears. And men no longer exhibit shifting interest for women based on their menstrual cycle, perhaps because those cues signaling ovulation are no longer present, scientists say.
Some women using birth-control pills have long reported changes to their libido and mood. Research is still in the early stages to explore the implications of taking hormonal contraceptives for women's choice of mates and for fidelity in relationships. Researchers speculate that women with less-masculine partners may become less interested in their partner when they come off birth control, contributing to relationship dissatisfaction. And, if contraceptives are masking women's natural ability to detect genetic diversity, then the children produced by parents who met when the woman was on the pill may be less genetically healthy, they suggest.
'We don't have enough research to draw a firm conclusion yet,' says Dr. Haselton. 'It is certainly possible that if women don't experience that little uptick in [desiring] masculinity that they end up choosing less masculine partners,' she says.
That could prompt some women to stray, research suggests. Psychologist Steven Gangestad and his team at the University of New Mexico showed in a 2010 study that women with less-masculine partners reported an increased attraction for other men during their fertile phase. Women partnered with traditionally masculine partners didn't have such urges, according to the study of 60 couples.
In another study, the researchers analyzed MHC gene samples of 48 couples. Women partnered with men with whom they shared the least genetic diversity reported being less sexually responsive to their mates. The study was published in 2006 in the journal Psychological Science.
There is also accumulating evidence indicating men react differently to women when they are on birth control. A 2004 study in the journal in Behavioral Ecology used the T-shirt study methodology but instead put the shirts on 81 women. A panel of 31 men, smelling the T-shirts, experienced the greatest attraction for the non-pill-using women when they were ovulating. Twelve women on the panel didn't detect any difference.
A study on primates appears to support the idea that hormonal contraceptives change mating preferences. Duke University researchers studied hormones secreted by female lemurs before and after the animals received a hormonal contraceptive. They also studied males' preferences for these scents.
The findings, published in the journal Proceedings of the Royal Society, Biological Sciences this year, showed that the injection of Depo-Prevara, a long-lasting contraceptive that is approved for use in humans, dramatically altered the chemicals that female lemurs give off to indicate their identity and how genetically healthy they are.
The females given the contraceptive became overall less appealing to the males than before getting the injection, says Christine Drea, a professor in Duke's evolutionary anthropology department and senior author on the study. The contraceptive erased all the normal information the odor signals conveyed, she says.
Though the study would need to be conducted in humans to draw direct conclusions, there are potential parallels to people, Dr. Drea says. Birth control 'could be mixing up your own [signals] and others aren't smelling the real you,' she says.
Shirley S. Wang
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