"Long before it's in the papers"
January 28, 2015


Even monkeys rationalize, study finds

Nov. 6, 2007
World Science staff
Note: this story has been corrected 
since its original posting. See below.

Af­ter we make a ques­tion­a­ble choice, we of­ten think up—or make up—new rea­sons to be­lieve it was right af­ter all. The pro­cess is called ra­t­ional­iz­a­tion; and al­though it seems point­less and sil­ly, it does some­times help us feel bet­ter about our­selves.

A capuchin monkey (courtesy U.S. Nat'l Science Foundation)

Now, re­search­ers have found that mon­keys do it, too. That raises the pos­si­bil­ity that the pro­cess is ev­o­lu­tion­arily much old­er, and per­haps more au­to­mat­ic, than was pre­vi­ously be­lieved, ac­cord­ing to the sci­en­tists.

Lou­i­sa Egan and col­leagues at Yale Un­ivers­ity in Con­nect­i­cut of­fered cap­u­chin mon­keys choices be­tween M&M can­dies of various col­ors. An ini­tial phase of the test­ing in­volved find­ing “three co­lors a mon­key liked equally—say, red, yel­low, and blue,” Egan wrote in an email. 

The investiga­tors would next give the pri­mate a choice be­tween two of these items; and finally, be­tween the just-rejected co­lor and the third. “For example, if the mon­key chose red over yel­low the first time, we then gave the mon­key a choice be­tween yel­low and blue the sec­ond time,” she explained.

The monkeys’ behavior then changed: a co­lor spurned once, seemed to be­come per­man­ently out­cast. “We found that a mon­key in this si­tu­a­tion would con­sis­tently pre­fer blue over yel­low, even though they liked red, yel­low, and blue equal­ly to start,” she wrote.

This suggests, she added, “that when the monkey chose red over yellow, he devalued the yellow as a means of rationalizing his decision.” Past ex­pe­ri­ments with hu­man adults have reached si­m­i­lar re­sults. The Yale group al­so re­peat­ed a ver­sion of the test with hu­man chil­dren, again with the same sort of out­come. 

“These re­sults pro­vide the first ev­i­dence of de­ci­sion ra­t­ional­iz­a­tion in chil­dren and nonhu­man pri­ma­tes,” the team wrote in the No­vem­ber is­sue of the re­search jour­nal Psy­cho­log­i­cal Sci­ence. Some psy­chol­o­gists pos­tu­late that ra­t­ional­iz­a­tion is a type of de­fense mech­an­ism, a men­tal pro­cess that low­ers stress by ex­pung­ing thoughts that might oth­er­wise threat­en our self-es­teem.

* * *

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Note: this article has been corrected since its original posting. It initially suggested erroneously that after making an initial choice between two colors they previously liked equally, monkeys be­gan to con­sist­ently choose again the col­or they had just cho­sen.


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After we make a questionable choice, we often think up—or make up—new reasons why it was right after all. The process is called rationalization; and although it seems pointless and silly, it does sometimes help us feel better about ourselves. Now, researchers have found that monkeys do it, too. That raises the possibility that the process is evolutionarily much older, and perhaps more automatic, than was previously believed, according to the scientists. The researchers, with Yale University in Connecticut, offered capuchin monkeys a choice between M&M of two colors for which they had, until then, shown equal preference. After they made the choice, though, the primates began to consistently choose again the color they had chosen in the first part of the experiment—as if they had now convinced themselves that the choice was correct. Past experiments with human adults have reached similar results. The Yale team, Louisa Egan and colleagues, also repeated a version of the test with human children, again with the same outcome. “These results provide the first evidence of decision rationalization in children and nonhuman primates,” the team in the November issue of the research journal Psychological Science. Some psychologists postulate that rationalization is a type of defense mechanism, a mental process that lowers stress by expunging thoughts that might otherwise threaten our self-esteem.