科技。

　　Exercise and addiction.

　　锻炼也会上瘾。

　　Fun run.

　　奔跑的奥秘。

　　People, it seems, have evolved to be addicted to exercise.

　　人类似乎在进化过程中对锻炼上瘾了。

　　AS THE legions of gym bunnies and jogging enthusiasts who race out into the spring sunshine every year clearly demonstrate, running can be fun. More specifically, running triggers the release of brain chemicals called endocannabinoids that create a potent feeling of pleasure. As their name suggests, these endocannabinoids work in the same way as the active ingredient of marijuana.

　　那一大批在春日和煦的阳光中奔跑着的健身爱好者无不向我们展示着奔跑的乐趣。更确切地讲，在奔跑时人体内有一种化学物质被释放，从而使人产生一种强烈的愉悦感。正如其名字的含义一般，这些endocannabinoids有着跟大麻中的有效成分一样的效果。

　　From an evolutionary standpoint this surge of endocannabinoids, and the "runner's high" it creates, make sense. For ancient humans, remaining fit enough to run after game and away from predators and enemies was vital for survival. Yet whether other mammals are also driven to exercise by endocannabinoids has remained a mystery. Now a study led by David Raichlen of the University of Arizona has revealed that the runner's high does exist in other species, but not in all.

　　从进化论的观点来看，人体内endocannabinoids水平的上升及由此而生的"赛跑者的亢奋"对人类的发展是有意义的。那些远古时代的人类，为了能够顺利追捕到猎物并从其他猎食者的追击中逃脱，必须将身体状态始终维持在一个良好的水平。既然人类如此，那么其他哺乳动物是否也会在endocannabinoids的内在驱动下而进行锻炼呢？这仍是个未解之谜。现在一项由Arizona大学的David Raichlen博士领衔的研究已经在其他哺乳动物体内---并非全部都有——发现了endocannabinoids的存在。

　　You expect me to what?

　　你猜我在干什么？

　　Dr Raichlen hypothesised that endocannabinoid-driven exercise highs would be found in those mammals that gain an evolutionary benefit from being fast on their feet: antelopes, horses and wolves, for example. However, he also thought that they would not be present in those which are known for being quick and agile, but not for running, like ferrets. To test these ideas, he and a team of colleagues devised an experiment that monitored the endocannabinoid levels of different species after they had been walking or running on a treadmill.

　　Raichlen先提出了一个假设：像羚羊，马和狼这样一些因拥有"飞毛腿"而在进化过程中受益的哺乳动物中也存在着"锻炼产生的兴奋"现象；而那些以灵动著称，却非凭奔跑文明的动物，如雪貂，则不会出现此现象。为了检验这些猜想，Raichlen和由其同事所组成的团队设计了一个实验——对在跑步机上行走，奔跑过后的动物体内的endocannabinoids水平进行监控。

　　The experimental animals in question were ten people, eight dogs and eight ferrets. Dr Raichlen had them run or walk on the treadmill for 30 minutes. Since running and walking speeds differ from species to species, the speed at which the treadmill moved was varied so that it raised the heart rates of the different participants to the same level. Running speeds were thus set at 2.5 metres a second for people, 1.83 for dogs and 0.84 for ferrets. Walking speeds were set at 1.25 metres a second for people and 1.1 for dogs. The ferrets proved too easily distracted to walk consistently on the treadmills and were thus left to sit quietly in their cages for this part of the study. Each participating animal ran for one session and walked for one other, and did so on separate days, to avoid exhaustion. Before and after each session, blood was drawn from each and the endocannabinoid levels in it were measured.

　　被考虑用来进行实验的动物有以下三种：十个人，八条狗和八只雪貂。Raichlen博士先让他们在跑步机上行走或奔跑30分钟。由于不同的动物速度不一，所以跑步机的传送带速度设置是以使不同动物的心率达到同一水平为依据。这样设置的结果便为：奔跑速度为人类2.5米/秒，狗1.83米/秒，雪貂0.84米/秒；行走速度为人类1.25米/秒，狗1.1米/秒。雪貂由于太易分心，没办法让它持续在跑步机上行走，所以在进行该部分实验时它们被留在了笼中静静地坐着。每只动物会跑一段走一段，为了避免动物们出现筋疲力尽的情况，实验是分成几天进行的。在实验前和试验后，动物们都会被抽血以检验其中的endocannabinoid水平。

　　The researchers report in the Journal of Experimental Biology that, after 30 minutes of walking (or sitting in a cage), participants' endocannabinoid levels did not rise. After running, however, the average human's endocannabinoid levels rose from 2.4 picomoles per millilitre (pmol/ml) to 6.1. Dogs showed a similar trend, with levels rising from 2.4 pmol/ml to 8.0. Ferrets were different. Although they did show an increase, from 3.0 to 3.9 pmol/ml, this was not a statistically significant rise. These findings suggest that dogs experience a "runner's high" but ferrets do not.

　　研究人员在《生物学实验》杂志中提到，在经过30分钟的行走（雪貂是呆在笼中）之后，参加实验的动物的endocannabinoid水平并没上升。然而在奔跑过后情况则有所不同：那10个人的平均endocannabinoid水平从2.4 pmol/ml上升到了6.1 pmol/ml。狗的变化趋势与人类似——由2.4 pmol/ml升至8.0 pmol/ml。唯独雪貂例外。他们的endocannabinoid水平虽亦有所上升——3.0 至 3.9 pmol/ml，但仍处于统计学上可不被纳入考虑的范围内。这些发现表明狗中同样存在着"赛跑者的亢奋"现象，而雪貂则没有。

　　Dr Raichlen argues that it makes sense for ferrets not to have systems that reward cardiovascular activity, since such exercise consumes a lot of energy, may cause injury, and is not crucial to the stealthy hunting technique of sneaking down burrows and killing rabbits in their sleep. What is not clear is whether the endocannabinoid reward is an ancient mechanism that has been lost on branches of the mammalian tree that do not need it, or is something that evolves quickly in species which become active. Given that humanity's arboreal simian ancestors would presumably have had little need to run, it is probably the latter. But to be sure Dr Raichlen will need to put animals far less co-operative than ferrets on the treadmill.

　　看来雪貂体内并不存在对心血管活动进行阳性强化刺激的系统，Raichlen博士认为这对雪貂的发展同样是有意义的，要知道太剧烈的运动会消耗掉过多的能量， 甚至引发受伤，且这并非是雪貂捕猎技术中的关键——它们一般只需偷偷溜进兔子窝并在兔子们熟睡时将其杀死即可。仍有待考证的是，究竟这种endocannabinoid刺激机制是从远古时代起即为哺乳类动物所拥有（但在一些不需此机制的哺乳类分支中渐渐退化），还是从某些活跃的个别物种中进化出来的？鉴于人类的祖先—类人猿是树栖动物，据推测它们很少有奔跑的需要，因此正确结论很可能是后者。但若要确认此假设，Raichlen博士需将更多如雪貂般不太合作的动物哄上跑步机。