為何30歲女人如豺狼，40歲女人如美洲獅

Men who cheat on their spouses have always enjoyed an expedient explanation: Evolution made me do it. Many articles (here is one, and here is another), especially in recent years, have explored the theory that men sleep around because evolution has programmed them to seek fertile (and, conveniently, younger) wombs.

男人在背叛了自己的妻子後，最愛用的推托之詞就是：這是男人的天性。尤其最近許多篇研究也為這些人背書：男人會到處拈花惹草是因為物種演化，使得男人天生就會找尋「肥沃」，或更貼切的說，「年輕」的子宮。

But what about women? If it's really true that evolution can cause a man to risk his marriage, what effect does that have on women's sexuality?

那麼女人呢？如果真的是物競天擇讓男人寧願冒著賠上自己婚姻的風險，那是什麼原因影響了女人的性慾呢？

A new journal article suggests that evolutionary forces also push women to be more sexual, although in unexpected ways. University of Texas psychologist David Buss wrote the article, which appears in the July issue of Personality and Individual Differences, with the help of three graduate students, Judith Easton (who is listed as lead author), Jaime Confer and Cari Goetz. Buss, Easton and their colleagues found that women in their 30s and early 40s are significantly more sexual than younger women. Women ages 27 through 45 report not only having more sexual fantasies (and more intense sexual fantasies) than women ages 18 through 26 but also having more sex, period. And they are more willing than younger women to have casual sex, even one-night stands. In other words, despite the girls-gone-wild image of promiscuous college women, it is women in their middle years who are America's most sexually industrious.

一篇最新的文章指出，物種演化也促成了女性在某些出乎意料之外的情況下，有更強的性慾望。德州大學心理學家大衛巴斯(David Buss)在三位研究生(列為此篇主要作者的Judith Easton，Jaime Confer以及Cari Goetz)的幫忙下，於七月在社會與人格心理學(Personality and Individual Differences)發表了一篇研究指出，他們發現在界於30歲及40歲出頭的女性，比起較年輕的女性們，有更強的性慾。而27歲到45歲間的女人，也比18歲到26歲的女孩，有更多且更強烈的性幻想。且她們對於逢場作戲的接受度也更高，即使是一夜情也可以。換言之，儘管那些在大學搞雜交的女大生形象在人們心中極為淫亂，但中年女性才是真正全美國最勤於性交的族群。

By contrast, men's sexual interest and output, usually measured by a reported number of orgasms per week, peaks in the teen years and then settles to a steady level (an average of three orgasms per week) for most of their lives. As I pointed out in March, most men remain sexually active into their 70s. According to the new study, as well as the study I wrote about in March, women's sexual ardor declines precipitously after menopause.

比較之下，男人的性趣與精蟲量，通常是以每星期的高潮次數來衡量：於青少年時期來到高峰，之後則以每週三次穩定下來。誠如我於三月份的文章裡指出，男人到了70歲還是會有性慾。而根據最新的研究及我三月份的報告，女人的性衝動於停經後才會急遽下降。

Why would women be more sexually active in their middle years than in their teens and 20s? Buss and his students say evolution has encouraged women to be more sexually active as their fertility begins to decline and as menopause approaches.

為什麼女人在她們來到熟女年紀時會比年輕小女孩們有更強的性慾？巴斯及他的學生們表示，因為物種演化，使得女人在她們生育能力下降及停經期接近時，會有更頻繁的性行為。

Here's how their theory works:
Our female ancestors grew accustomed to watching many of their children — perhaps as many as half — die of various diseases, starvation, warfare and so on before being able to have kids of their own. This trauma left a psychological imprint to bear as many children as possible. Becoming pregnant is much easier for women and girls in their teens and early 20s — so much easier that they need not spend much time having sex.

以下是他們提出的理論：
我們的女性祖先，在她們能夠生小孩之前，已習慣於看到多數(可能多達一半)的小孩，死於疾病、飢荒、戰爭等等事件。這樣子的心理創傷，在她們心裡無形間埋下了「盡可能生越多的小孩」的想法。而懷孕對於20歲出頭的女孩子來說是很簡單的事情，以致於她們不用花太多的心思在生小孩這件事情上。

However, after the mid-20s, the lizard-brain impulse to have more kids faces a stark reality: it's harder and harder to get pregnant as a woman's remaining eggs age. And so women in their middle years respond by seeking more and more sex.

然而，過了25歲以後，她們的腦幹對於「生小孩」這件事，面臨了一件殘酷的事實：對於一個熟女的卵子來說，懷孕可以說是越來越困難了。於是，女人到了她們的中年時期後，就開始追求頻繁的性行為。

To test this theory, Buss and his students asked 827 women to complete questionnaires about their sexual habits. And, indeed, they found that women who had passed their peak fertility years but not quite reached menopause were the most sexually active. This age group — 27 through 45 — reported having significantly more sex than the two other age groups in the study, 18 through 26 and 46 and up. Women in their middle years were also more likely than the younger women to fantasize about someone other than their current partner. The new findings are consistent with those of an earlier Buss paper, from 2002, which found that women in their early 30s feel more lustful and report less abstinence than women in other age groups. In both studies, these findings held true for both partnered and single women, meaning that married women in their 30s and early 40s tend to have more sex than married women in their early 20s; ditto for single women. Also, whether the women were mothers didn't matter. Only age had a strong affect on women's reported sexual interest and behavior.

為了證實這個理論，巴斯和他的學生們邀請了827位女性來完成有關她們性習慣的問卷調查。的確，他們發現那些過了生育能力最強時期，而未到達停經期的女性們，擁有的性行為是最多的。這些27歲到45歲族群的女性，比起那些18到26歲，及46歲以上的女性，有更強的性慾望。而處於中年的女性們，也較那些年輕的女孩們，對於伴侶外男人的性幻想有更高的比例。這也與巴斯在2002年發表的研究相符，該研究指出：30歲出頭的女人，比起其他族群的女性，會感覺自己有更高的性慾(或更淫蕩)，且更難有禁慾的想法。這兩個報告也不約而同地得到了一個實證：30歲到40歲出頭的女性，無論已婚或未婚，都比其他族群的女性有更高的性慾。而且，無論該女性是否已為人母，只有「年齡」才會對於女人的性趣及性行為有明顯的影響。

And yet there are a few flaws with the data in the new paper. Chiefly: some three-quarters of the participants in the study were recruited on Craigslist, a website where many go to seek hookups, meaning there was a self-selection problem with the sample. (The other participants were students at the University of Texas in Austin.) The authors also note that there are some alternative explanations for why women in their 30s and early 40s might be more sexual. Many of them may simply be more comfortable with sex than women in their teens and early 20s. Still, that raises the question of why they are more comfortable: perhaps evolution programmed that comfort.

然而，這份新的報告也有幾個美中不足的地方。首先，這個研究的參與者有四分之三來自Craigslist網站，有許多人都來這個網站尋求社交配對，這也意味著這樣的樣本有自我選擇偏差方面的問題存在(其他的樣本則來自德州大學的學生)。而作者也備註了一些對於熟女們性慾較高的不同解釋：許多熟女們純粹對於「性」這方面較年輕女孩感覺自在；當然，這又冒出了一個為何她們感覺較自在的問題：或許是因為物種演化給了她們這份自在感吧！

Buss is the author of The Evolution of Desire: Strategies of Human Mating, now in its fourth edition, and has become associated with evolutionary explanations for sexual behavior. His theories help explain why men can be cads — and why women can be cougars.

巴斯同時也是「慾望進化論：人類性交策略」(The Evolution of Desire: Strategies of Human Mating)一書的作者，此書目前推出了第四版，它也對於人類的性行為以演化的概念提出了解釋。巴斯的理論解釋了為何男人會成為負心漢，同時也解釋了為何女人會成為美洲獅。

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