Are you a social butterfly, or do you prefer being at the edge of a group of friends? Either way, your genes and evolution may play a major role, US researchers reported on Monday.

    While it may come as no surprise that genes may help explain why some people have many friends and others have few, the researchers said, their findings go just a little farther than that.

    "Some of the things we find are frankly bizarre," said Nicholas Christakis of Harvard University in Massachusetts, who helped conduct the study.

    "We find that how interconnected your friends are depends on your genes. Some people have four friends who know each other and some people have four friends who don't know each other. Whether Dick and Harry know each other depends on Tom's genes," Christakis said in a telephone interview.

    Christakis and colleague James Fowler of the University of California San Diego are best known for their studies that show obesity, smoking and happiness spread in networks.

    For this study, they and Christopher Dawes of UCSD used national data that compared more than 1,000 identical and fraternal twins. Because twins share an environment, these studies are good for showing the impact that genes have on various things, because identical twins share all their genes while fraternal twins share just half.

    "We found there appears to be a genetic tendency to introduce your friends to each other," Christakis said.

    There could be good, evolutionary reasons for this. People in the middle of a social network could be privy to useful gossip, such as the location of food or good investment choices.

    But they would also be at risk of catching germs from all sides -- in which case the advantage would lie in more cautious social behavior, they wrote in the Proceedings of the National Academy of Sciences.

    "It may be that natural selection is acting on not just things like whether or not we can resist the common cold, but also who it is that we are going to come into contact with," Fowler said in a statement.

    你是愛好交際還是喜歡獨來獨往？美國研究人員于本周一報告稱，不管你屬于哪一類，你的基因及進化過程可能在這一問題上起著重要的作用。

    研究人員稱，用基因解釋為什么有些人朋友眾多而有些人卻寡朋少友其實并不新鮮，不過他們的研究更深入一些。

    來自馬薩諸塞州哈佛大學的尼古拉斯•克里斯塔奇斯協助開展該研究，他說：“我們發現的一些現象的確很奇怪。”

    克里斯塔奇斯在一次電話采訪中稱：“我們發現一個人朋友之間的親密程度取決于這個人的基因。有的人有四個朋友而且互相認識；而有的人有四個朋友，但他們卻素不相識。也就是說，迪克和哈利是否互相認識是取決于湯姆的基因。”

    克里斯塔奇斯和他的同事、來自加利福尼亞大學圣地亞哥分校的詹姆斯•福勒此前以研究肥胖、吸煙以及快樂會在朋友之間傳播而著名。

    在這項研究中，他們和加利福尼亞大學圣地亞哥分校的克里斯托弗•道維斯使用了一項全國性數據，這項數據對1000多對同卵及異卵雙胞胎的基因進行了對比。由于雙胞胎生活在同一個環境，而且同卵雙胞胎的基因完全相同，而異卵雙胞胎有一半的基因相同，所以這些研究有助于發現基因對人各個方面的影響。

    克里斯塔奇斯說：“我們發現人們在介紹朋友互相認識時有一個基因傾向性。”

    這種傾向性可以用合理的、進化方面的原因來解釋。處于社交圈中的人們可能會參與一些有用信息的傳播，比如哪些地方有吃的，或者好的投資選擇等等。

    但研究人員在發表于《國家科學院院刊》上的研究報告中稱，在這一過程中，人們也會受到來自各方的一些不利影響——由此說來，只有謹慎的社交活動才能給人帶來好處。

    福勒在一份聲明中說：“可能自然選擇不僅會影響我們是否能夠抵抗普通感冒之類的問題，它對我們接觸什么樣的人也有影響。”