This is Scientific American — 60-Second Science. I'm Christopher Intagliata.
If I buy you lunch today, chances are you'll pick up the tab next time. We humans reciprocate a lot... days, weeks or even months later. And other primates do it too. Monkeys that are more generous with food, for example, enjoy more grooming from their peers... and they're more likely to get backup later on in a fight.
Now a new study suggests a nonprimate, the dwarf mongoose, also makes cooperative, time-delayed barters... trading grooming for guard duty. Here's how it works.
"When an individual is on sentinel, they are basically on guard duty for the rest of the group." Julie Kern, a behavioral ecologist University of Bristol. "So they will choose an elevated position like a tree or a termite mound from which to sit and then they watch out for predators that are might be coming in to target the group. And then they'll give alarm calls, (alarm calls) to warn the rest of the group."
But throughout the watch, they also remind everyone they're on lookout, with softer surveillance calls (surveillance calls). So any mongooses hunting for bugs can keep calm and carry on.
What Kern and her colleagues observed in the wild was that mongooses who took those lookout shifts also enjoyed more grooming back at the burrow. Then, to establish cause and effect, they played recordings of certain mongoose individuals making surveillance calls — in effect tricking the mongoose's peers into thinking it was on guard duty. And indeed, the supposed sentry was rewarded with more grooming later on... suggesting that dwarf mongooses trade favors, even after time has passed.
The details are in the Proceedings of the National Academy of Sciences.
Not to say mongoose society is quite as complex as ours. "I think there are obviously ways in which we track contributions which are very different to what's going on here." But at a very basic level — it appears mongoose society also follows the rule, "You scratch my back, and I'll scratch yours."
Thanks for listening for Scientific American — 60-Second Science. I'm Christopher Intagliata.
如果我今天请你吃午餐，那下次可能由你来买单 。我们人类经常互相回报——无论是几天、几周甚至几个月后 。其他灵长类动物也会这样做 。例如，更慷慨分享食物的猴子会有更多同伴为其梳毛，而且日后在打架时也可能得到支援 。
现在，一项新研究表明，侏獴这种非灵长类动物也会进行合作性的、时间延迟的交换——用梳毛来换警卫 。下面来解释一下它们的交换原理 。
“当个体侏獴放哨时，它们基本上是在为这个群体的其它成员站岗守卫 。布里斯托尔大学的行为生态学家朱莉·克恩说到 。“所以它们会选择坐在树上或白蚁丘等较高位置，提防可能会来攻击群体的捕食者 。发现情况时它们会发出警报呼叫（警报呼叫），提醒群体里的其它成员 。”
但在整个警戒过程中，它们也会发出较轻柔的监视呼叫，以提醒其它成员它们在放哨（监视呼叫） 。这样一来，找虫子的侏獴就可以保持冷静，继续找虫子 。
克恩和同事在野外观察时发现，轮班警戒的侏獴回到洞穴后会享受到更多的“梳背”服务 。然后，为了建立因果联系，他们播放了某只侏獴发出的监视呼叫声音——这实际上是在欺骗侏獴，让它们以为有成员在放哨 。确实，之后被认为是“哨兵”的侏獴得到了更多的梳毛服务 。这表明侏獴会交换利益，即使已经过了一段时间 。
这并不是说侏獴社会像我们人类社会那样复杂 。“我认为，我们在追踪记录侏獴的互相回报时，有一些明显且不同的方法 。”但从非常基础的层面来说，似乎侏獴社会也遵循“投桃报李”这一规则 。
谢谢大家收听科学美国人——60秒科学 。我是克里斯托弗·因塔利亚塔 。
1. pick up the tab (替一群人)付账，承担费用；
Pollard picked up the tab for dinner that night.
2. trade sth. for sth. 用…进行交换；互相交换；
Tom made me an offer I couldn't refuse. He asked me to tr ade his computer for my old cell phone. He must be crazy!
3. watch out for 密切注意；戒备；提防；
He called out to them to watch out for the unexploded mine.
4. in effect 其实；实际上；
In effect, the two systems are identical.