出處：Web Only 2009/09
為何男性的肌肉比女性大那麼多？男性負責戰鬥和打獵當然是原因之一，女性喜歡擅長戰鬥和打獵的男性，因此會被肌肉大的男性吸引，可能也是原因之一。雄鹿的角、雄孔雀的尾巴，都是性選擇的產物，而William Lassek和Steven Gaulin相信，男性的肌肉也是如此。
The Economist
Mr Muscle
By The Economist print edition
From The Economist
Published: September 04, 2009
WHY are men's muscles so much bigger than women's? Partly, of course, because men do the fighting and hunting. But also, perhaps, because women like men who can do these things well, and are thus attracted to muscular men. Both phenomena—competing with members of the same sex and showing off to members of the opposite—are subject to a form of evolution known as sexual selection. It is sexual selection that created the deer's antlers and the peacock's tail, and William Lassek of the University of Pittsburgh and Steven Gaulin of the University of California, Santa Barbara, think it explains men's muscles as well.
The main characteristic of sexually selected features is that they are expensive to maintain. Since, whether competing or attracting, only the best will do, resources get piled into them, almost regardless of the consequences. In a study just published in Evolution and Human Behavior, Dr Lassek and Dr Gaulin show that this crucial characteristic is true for men's muscles.
Their data came from the National Health and Nutrition Examination Survey, which followed 12,000 American men and women over the course of six years. They found that men require 50% more calories than women do, even after adjusting for activity levels, and that their muscle mass is the strongest predictor of their intake of calories—stronger than their occupation or their body-mass index (a measure of obesity). And there is another cost to being muscly: men's immune systems are less effective than those of women (which was known before), and become worse the more muscular the men are (which was not).
The benefits, however, were there, as well. The more muscular a man, the more sexual partners he reported, both in the past year and over his lifetime, and the earlier his first sexual experience was likely to have been. This may, in part, be a result of the ability of muscular men to intimidate 97lb weaklings. But in a society where extreme forms of such intimidation are curbed by law, female choice seems as likely an explanation—especially as previous studies have confirmed scientifically the everyday observation that women do indeed prefer men with big biceps and triangular torsos.
Because muscles come at such cost, Dr Gaulin thinks an evolutionary fight is going on between natural selection, which conserves metabolic expenditure and promotes longevity, and sexual selection, which willingly trades both for extra mating opportunities. This may explain why men have such a range of muscularity. In the past, the strong man would have had better mating opportunities in the short term, but the skinny guy who outlived him could have had just as much reproductive success over the course of his longer life.
The irony for the skinny guy is that the laws which protect him from aggression also make it less likely that the hulk will fight himself into an early grave. Modern medicine, meanwhile, means the hulk's weakened immune system is less likely to expose him to lethal infection. Time, then, to get the weights out, and start pumping iron.
性擇特徵得花很多成本來維持。Lassek和Gaulin博士最近發表的研究發現，即使調整活動量後，男性需要的卡路里還是比女性多50%。以肌肉量預測男性吸收的卡路里量非常準確，比職業或BMI指數更準。但是肌肉大的男性免疫系統不如女性，而且肌肉越大的人越差。他們的資料來自國家健康及營養調查，該調查追蹤12000名美國男女性，為時6年。
不過，越壯的男性性伴侶越多，初次性經驗也比較早。這也許是因為壯漢有能力威嚇瘦弱的人，但現在法律限制強烈威嚇，女性的選擇似乎才是原因──過去的研究也證明，女人確實比較喜歡二頭肌大塊、身材呈倒三角形的男人。
大肌肉有代價，Gaulin博士相信這是天擇（節省新陳代謝、追求長壽）和性擇（犧牲二者換取更多交配機會）間的進化戰爭。這可以解釋為何人類有各種不同的健壯程度。過去，強壯者在短期內有較多交配機會，但瘦弱者活得比較久，繁殖機會不輸強壯者。
諷刺的是，法律保護瘦子免受壯漢攻擊，也讓壯漢比較不會因爭鬥而早亡。而在現代醫學進展下，免疫系統較差的壯漢碰上致命感染的機會也更低，壯漢也能追求長壽。該是時候開始練身體了。（黃維德譯）
The main characteristic of sexually selected features is that they are expensive to maintain. Since, whether competing or attracting, only the best will do, resources get piled into them, almost regardless of the consequences. In a study just published in Evolution and Human Behavior, Dr Lassek and Dr Gaulin show that this crucial characteristic is true for men's muscles.
Their data came from the National Health and Nutrition Examination Survey, which followed 12,000 American men and women over the course of six years. They found that men require 50% more calories than women do, even after adjusting for activity levels, and that their muscle mass is the strongest predictor of their intake of calories—stronger than their occupation or their body-mass index (a measure of obesity). And there is another cost to being muscly: men's immune systems are less effective than those of women (which was known before), and become worse the more muscular the men are (which was not).
The benefits, however, were there, as well. The more muscular a man, the more sexual partners he reported, both in the past year and over his lifetime, and the earlier his first sexual experience was likely to have been. This may, in part, be a result of the ability of muscular men to intimidate 97lb weaklings. But in a society where extreme forms of such intimidation are curbed by law, female choice seems as likely an explanation—especially as previous studies have confirmed scientifically the everyday observation that women do indeed prefer men with big biceps and triangular torsos.
Because muscles come at such cost, Dr Gaulin thinks an evolutionary fight is going on between natural selection, which conserves metabolic expenditure and promotes longevity, and sexual selection, which willingly trades both for extra mating opportunities. This may explain why men have such a range of muscularity. In the past, the strong man would have had better mating opportunities in the short term, but the skinny guy who outlived him could have had just as much reproductive success over the course of his longer life.
The irony for the skinny guy is that the laws which protect him from aggression also make it less likely that the hulk will fight himself into an early grave. Modern medicine, meanwhile, means the hulk's weakened immune system is less likely to expose him to lethal infection. Time, then, to get the weights out, and start pumping iron.
性擇特徵得花很多成本來維持。Lassek和Gaulin博士最近發表的研究發現，即使調整活動量後，男性需要的卡路里還是比女性多50%。以肌肉量預測男性吸收的卡路里量非常準確，比職業或BMI指數更準。但是肌肉大的男性免疫系統不如女性，而且肌肉越大的人越差。他們的資料來自國家健康及營養調查，該調查追蹤12000名美國男女性，為時6年。
不過，越壯的男性性伴侶越多，初次性經驗也比較早。這也許是因為壯漢有能力威嚇瘦弱的人，但現在法律限制強烈威嚇，女性的選擇似乎才是原因──過去的研究也證明，女人確實比較喜歡二頭肌大塊、身材呈倒三角形的男人。
大肌肉有代價，Gaulin博士相信這是天擇（節省新陳代謝、追求長壽）和性擇（犧牲二者換取更多交配機會）間的進化戰爭。這可以解釋為何人類有各種不同的健壯程度。過去，強壯者在短期內有較多交配機會，但瘦弱者活得比較久，繁殖機會不輸強壯者。
諷刺的是，法律保護瘦子免受壯漢攻擊，也讓壯漢比較不會因爭鬥而早亡。而在現代醫學進展下，免疫系統較差的壯漢碰上致命感染的機會也更低，壯漢也能追求長壽。該是時候開始練身體了。（黃維德譯）
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