一個接受過別人幫助的人,，往往會更愿意給予其他需要的人以同樣的幫助，這種“投桃報李”的行為一直被認為是人類特有的美德,。然而,，科學家卻在近日發(fā)現，這種美德并非只存在于人類身上：一只老鼠在接受其他同類的幫助后，也會變得更加“樂于助人”,。
“一般性互惠”現象
據發(fā)布在PLoS Biology雜志上的最新文章表面,，這種被稱為“一般性互惠”的現象，以前只在人類身上發(fā)現過,。為了解釋“一般性互惠”現象,，瑞士伯爾尼大學的邁克爾·塔波爾斯基舉了一個例子：當一個人在電話亭里撿到別人留下的錢之后，他會更愿意幫助其他陌生人,。
塔波爾斯基表示,，人類社會中存在的這種“投桃報李”現象，雖然也可以用文化方面的原因來解釋,，但如果在其他動物身上也發(fā)現類似的行為,，則說明“投桃報李”更有可能是一種進化現象。
隱藏進化機制
為了測試動物中的“投桃報李”行為,，塔波爾斯基對一些老鼠進行了訓練,，讓它們學會抬起一個杠桿。當這個杠桿被抬起來時,，另一只老鼠就可以吃到食物,，不過抬起杠桿的那只老鼠卻吃不到。研究人員發(fā)現,，和沒有吃到這種免費食物的老鼠相比,，那些受過別人恩惠的老鼠，會有20％的概率更愿意幫助其他陌生同類,。
塔波爾斯基認為,，這種行為并不只存在于老鼠和人類之中。他說：“我相信,，‘一般性互惠’現象是廣泛存在的,，在許多不同的動物種類中都能發(fā)現這種現象，而我們的研究也表明,，這種現象之下隱藏著一種進化機制,。”
具有重要的進化意義
對于生物學家而言，解釋動物之間的合作現象一直是個棘手問題,。根據達爾文的進化理論,，各種生物體總是最大限度地增加自己生存的機會，那么這種“投桃報李”的現象又該如何解釋呢,？
對此,，一種解釋是，這只動物幫助其他同類,，是為了以后得到對方的幫助,。不過,，這樣做無疑很容易受騙，因為它可能會遇到一個只愿索取,、不愿回報的對象,。
另一種解釋是，在動物中也存在“一般性互惠”現象：一只動物會認為,，自己與任何其他個體最近一次的互動,，代表了它所生活的整個社會的一般行為。在這種情況下,，動物不需要記住特定的幫助者,。塔波爾斯基表示：“這種機制更加簡單，因此可能具有更加重要的進化意義,。”
英文原文：
Source: Public Library of Science
Date: July 5, 2007
Altruistic Rats: First Evidence For Generalized Reciprocal Cooperation In Non-humans
Science Daily — Cooperation in animals has long been a major focus in evolutionary biology. In particular, reciprocal altruism, where helpful acts are contingent upon the likelihood of getting help in return, is especially intriguing because it is open to cheaters. In a new study published this week in the open-access journal PLoS Biology, Claudia Rutte and Michael Taborsky demonstrate the first evidence for generalized reciprocal cooperation in non-humans. The authors show that rats who received help in the past were more likely to help another unknown partner.
Although many models have predicted reciprocal altruism, scientists had found evidence only of direct reciprocity ("if you help me, I'll help you") in non-human animals in previous studies. Direct reciprocity is intuitively appealing, yet requires that animals interact repeatedly with the same individuals and remember past interactions. By comparison, generalized reciprocity makes no such cognitive assumptions. In generalized reciprocity, animals are more likely to help a partner if they have been helped in the past, regardless of the past helper's identity.
For example, in humans, people who found a coin in the coin return of a telephone were more likely to help a stranger pick up dropped papers than control subjects who had not previously found money. In humans, this can be explained by cultural experience as well as by natural selection. But if similar reactions to anonymous experience can be found in non human animals, an evolutionary explanation would be far more likely.
In this study, rats received help gaining food from a partner who pulled a stick to produce the food. Rats could therefore be grouped into two classes: those that had previously received help and those that had not. The rats who had previously been helped were then more likely to help another unknown partner receive food. (Credit: iStockphoto/Leroy Dickson)
In this study, Norway rats received help gaining food from a partner who pulled a stick to produce the food. Rats could therefore be grouped into two classes: those that had previously received help and those that had not. The rats who had previously been helped were then more likely to help another unknown partner receive food. This simple mechanism may promote the evolution of cooperation among unfamiliar non-relatives in many other animals.
Citation: Rutte C, Taborsky M (2007) Generalized reciprocity in rats. PLoS Biol 5(7): e196. doi:10.1371/journal.pbio.0050196.
Note: This story has been adapted from a news release issued by Public Library of Science.
