新托福阅读材料：MiceShowHeritableDesireForExercise

会计考友

什么有些人爱运动，能持之以恒的锻炼身体而有些人却不爱运动呢?除了个人性格因素之外还能有什么原因么?也许一项最新的研究能回答这个问题，爱运动的习惯与遗传也有关，至少在老鼠身上做的实验结果如此。  
2 l" b. b7 b+ Z& Q8 O9 }　　Always finding excuses to skip the gym? Congrats—you might be able to blame your genes. Because the mere desire to exercise may be inherited, at least in mice. So says a study in the journal Proceedings of the Royal Society B. [Theodore Garland Jr. et al, http://bit.ly/crWNGd]

% X& \5 C, n- K5 _　　The experiment started back in 1993 with 224 mice, divided into eight groups. In four of the groups, the researchers mated the males and females that logged the most distance on their exercise wheels. For the other four groups, they just randomly bred the mice.

　　Forty-three generations later, the mice descended from long distance runners are voluntarily running seven miles a day—three times as far as their lazy counterparts. And they cover those miles in different ways—some are marathoners, while others, especially females, run faster for fewer hours.
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　　The running mice do have physical advantages, like better endurance and less body fat. But it's not just fitness. Previous studies suggest something's changing in the mice's brains too, turning them into exercise addicts. And since mice and humans have similar genes, our itch to hit the track might also depend on how often mom and dad liked to throw on their running shoes.