The Roots of Racism in Rhesus Monkeys

Why our prejudices may be deeply ingrained in our evolutionary development.
  • Transcript


Question: Can monkeys have human-like prejudices?

Laurie Santos: Our newest line of work is actually trying to explore whether or not the monkeys share some of the aspects of human social cognition that we’re not very proud of.  So these are things like the fact that we are very, very prejudiced. Even though we don’t realize we are, we have these implicit biases against out-group members, against individuals of different religions, different races and so on. And these biases play themselves out in really insidious ways.  We’d really like to know how these biases work, but there are lots of possibilities on the table for where they come from. Like, you know, we grow up in a biased society, there are lots of kinds of cultural influences that are biases.  Are these the real culprits, or is it something a little bit deeper?  Is it something maybe older that might be harder to override?
So we actually started studying whether the monkeys share some of our human-like prejudice against the out-group. Our first study really just asks this in a really simple way. We said, "Do monkeys spontaneously distinguish between guys that are in their in-group and guys that are in the out-group?"  So the experiment was super-simple. We did this down at our field site in Puerto Rico, where we study Rhesus monkeys. Monkeys free range around and we sort of showed up with this sort of big billboard which had two covers at the end of it.  When we opened the covers, there were two pictures of different monkeys.  One guy from their group and one guy from their out-group. And the really simple measure was, do the monkeys increase their vigilance, kind of get worried about it and stare at more the guy that is in the out-group? Again, this is you know, first trial monkeys that have ever really seen this weird billboard set up. But we found the expected result what you might expect from humans, which is that, spontaneously the monkeys actually direct their vigilance towards the guy who is in their out-group. The worrying thing seems to be very similar to the way that humans can devote their attention to out-group members. 
And in our next line of studies, we wanted to see, "Well, are they just kind of looking longer at these guys, or do they actually treat them differently?"  In other words, do they associate them with bad things in their environment?  And there’s a long line of studies in people trying to look at whether people do this implicitly.  There’s a study known as the "Implicit Association Test" which basically asks you to do a couple of categorizations. You’re categorizing good and bad words, and you’re also categorizing in-group and out-group members, you know say, your religion versus a different religion. 
And using this task, researchers have shown that it’s actually very hard to categorize your in-group with the bad words, and your out-group with the good words.  You’re actually slower and you make more errors when these categories don’t match up.  Suggesting that even though we don’t like to think we do, we have these biases against out-group members that can play out in these really simple contexts. 

So we basically did the same categorization measure with our monkeys.  We gave them kind of series of different pictures that either matched in their valance.  So they were all kind of good images to the monkeys, or they were all bad images to the monkeys.  The idea in those cases was the monkey should get bored, kind of good thing, good thing, good thing, or bad thing, bad thing, bad thing.  Or we set up a list of pictures where the valances differed. And one of these cases was one of pictures of their in-group members and pictures of bad things in this case scary spiders.  And what you found was that when the valances were inconsistent—so in other words, when the in-group members were paired with these bad spiders—that actually increased the monkeys' processing time suggesting they don’t treat those categories the same way. However, when you put out-group members with bad things, like spiders, they actually process them very quickly suggesting that, to a monkey a member of it’s out-group is basically, in some sense, equivalent emotionally or in terms of its valance to this scary predator spider creature. 
Same thing when we tried to look at positive images.  So, in-group members, the monkeys seems to process, like fruits really positive, you know, good images that they want to approach and come near. But not so with out-group members.  So, when you give them pictures of out-group members paired with fruits, it actually takes them a lot of processing time.  What it seems like is that spontaneously the monkeys are setting up the same associations that we humans are, where they are treating out-group members like negative things and in-group members like positive things.
Is it difficult to determine which monkeys are "in" and which monkeys are "out" of the group?

Laurie Santos: For monkeys, in-groups and out-groups are very simple. For humans, it’s not that simple, right?  We can form groupings based on all kinds of really stable social groups like our race, our gender, and so on.  But we also form groups on the fly.  You know, we can be Red Sox fans or Yankees fans. You know I can be the gray shirt-wearing person; you could be a different color shirt-wearing person.  Humans can turn these things on really spontaneously. For the monkeys, it depends on how they’re born. So the monkeys in this population are born into a particular social group.  It’s based on who they’re related to, so they are born into a particular group, the females stay in that group for their whole lives and the males actually switch groups. 
So, the monkeys provide this really cool window because the females live in these very stable groups that they’re going to be in for their whole lives, where the males actually switch.  And so the males actually, you know, are in one group for a certain stage of their lives and then switch to a new group.  So they kind of, in some sense, have to update their information about what group they’re in, who they like, and who they don’t like and so on.
What does the Rhesus monkeys’ behavior tell us about human groups?

Laurie Santos:
Our conclusion from this recent line of work suggests that... first that monkeys actually spontaneously form associations, form categories of out-groups in the same way that humans do.  So, the perhaps the exact same thing that humans do when they think about individuals from a different race, the monkeys are doing when they are thinking about individuals from a different social group.  Beyond just the fact that they categorize them, they also seem to valance them in the same way as humans do. Mainly that they tend to think of the in-group as a positive entity, maybe actually devote resources more to the in-group, and they think of the out-group as a negative entity. 
The thing in humans is that we know that this is true implicitly, often explicitly people won’t express these prejudices.  But it suggests that whatever is going on at the implicit level might be a process that’s evolutionarily quite old.  And to us that suggests that getting over these kinds of biases might even be harder than social psychologists have thought before. 
The monkey work is cool because, what we think it’s telling us is something about the roots of human sexism, human racism, human ageism, basically any form of human group ism—we’re seeing the undercurrents of this in the same cognitive processing we’re studying in the monkeys. 

Recorded May 21, 2010
Interviewed by Andrew Dermont