As humans, we know how important social interactions are. Aside from the importance of immediate family members, we also like to socialize with new people, unrelated people, and generally just people. There are several other species which are also known to be very social, and I'm not talking about bees. In mammals, the size of the frontal cortex, which is very important for higher informational processing, actually varies according to how high the group size of the species generally is. For example, macaques, a very social species, have large frontal cortices,while less social species of primates do not.
Social information is extremely important to primates, including humans. For example, in a job environment, it's very important to know who your boss is, who's under you, and who your direct peers are. In a social group, there are usually undeclared leaders and followers. And in any social situation, you NEED to know who the hot member of the species is over there.
Of course, most things that are necessary for survival become things that are worth doing for other reasons. Thus, social interaction is not only good for us, it FEELS good (for most of us, anyway). We like hanging out with other people, and we especially like (and work hard to) hanging out with those who we perceive to be more powerful or sexually available. And of course it's the same for other primate species such as monkeys, who want to obtain information about other animals in their environment.
But the question is, how worth it is it to hang out with, or obtain information about, other individuals in your social environment? And what would a monkey pay to look at this hotness?
Oh yeah, you know you'd pay good money to see that.
Deaner et al. "Monkeys Pay Per View: Adaptive Valuation of Social Images by Rhesus Macaques" Current Biology, 2005.
In this study, the authors wanted to know what, to the monkeys, was worth looking at, and thus obtain information on how the monkeys obtain and value information about status cues from other monkeys. To do this, they trained a group of monkeys on a "common fluid currency" system. That might sound like a big economic deal, but don't be fooled: it's juice. Monkeys LOVE juice, and so in this case it served as a "currency" which they could use to "pay" for views of other monkeys. Basically, each task went like this:
What you can see up there is the form of the task. It starts with a monkey in a chair (preferably one that wants some juice), facing a computer screen, on which they fix their eyes. Then the monkey is given a choice between two targets, T1 and T2. If he focuses on T1, he'll get some juice. If he focuses on T2, he'll get juice and a picture of another monkey. The choices the monkeys is given are a high ranking monkey's face, a low ranking monkey's face, or a hot piece of female monkey butt, in a pink color indicating that she's in estrous and ready to mate.
Then, they varied the amount of juice that the monkey would have to get, some images were associated with higher amounts of juice, and some with lower amounts of juice. Monkeys were trained to know what combinations to expect out of the target+photo combination, and could then choose their target appropriately. As each image was associated with at least a little bit of juice, images associated with less juice were considered "payment" (they could get more juice by looking at the juice target), and images associated with more juice than average indicated the monkeys were being paid to view the images.
What they saw was something like this:
The X axis of the graph here (the horizontal axis) shows the percentage of juice in comparison to a normal amount, so +25% meant that they got 25% more juice. The Y axis (the vertical axis) shows the amount of times the monkeys picked the image option at that particular juice concentration. You can see the two curves here, the red representing the female's perineum (the female monkey's butt), and the green showing a low status monkey's face relative to the monkey being tested.
What is important here are the differences between the two curves. You can see that the green curve is far to the left of the red curve. What this signifies is that for the red curve, monkeys were willing to give up a pretty significant amount of juice to view some hot female butt, but that they actually had to get at least an average or above average amount of juice to look at a low ranking monkey's face. So this means two things: (1) that monkeys will pay to views things of importance to them, like high ranking money faces and hot monkey butts, but have to BE paid to views things of little use to them, like a low ranking monkey, and (2) that a hot butt is better than an ugly face (male monkeys did not overly value looking at female faces, the butts were far more appealing).
Interestingly, the monkeys, once their choice was made, did not differ in the amount of time spent staring at the images. This is possibly because prolonged staring among monkeys is taken as a social threat (keep this in mind if you go to a zoo, don't stare straight at them if they are looking at you, look at them instead out of your peripheral vision. Makes everyone much more comfortable).
The authors also did one more experiment, to examine how the monkeys reacted to the images. They noticed that the monkeys managed to relate to all of the images they saw relative to their own social status. High ranking monkeys disdained far more images of all the monkeys beneath them, while lower ranking monkeys looked at more images and sacrificed juice for images that were not highly ranked. In order to examine how the monkeys judged their own social status, they did something interesting: they put mirrors in the monkey's cages. Then they measured the time that the monkeys spent gazing captivated by their own reflection. It turns out that highly ranked monkeys are very vain indeed, spending up to 41% of their time staring in the mirror. Low ranking monkeys, on the other hand, had pretty low self-esteem, spending only 19% of their time staring in the mirror. This may help the high ranking monkeys know not only that they themselves are high ranking, but also what makes a high ranking monkey, and thus what to identify when looking for a high-ranking face.
What does this all mean? It means that monkeys value different kinds of social information differently, according to it's usefulness in the wild. You need to know who your boss is, and you need to know who the hot chick with the red butt is. It also shows that monkeys can discriminate against other monkeys based on social status, and that they can do this based on looks alone, without having to see the behavior of other monkeys toward the individual. It is possible that facial recognition of the individuals made the monkeys just remember who was a dig deal and who was an average joe (the monkeys and images were all from the same colony and all knew each other), but together with the information from mirror-staring, this also implies that monkeys might have certain physical features in mind when they look for monkeys of high status.
So I suppose next time you pay money for that copy of that crappy magazine at the grocery store checkout featuring the lifestyles of the rich and famous, you could feel a little bit better. You're only paying for an opportunity to look for high ranking faces. And possibly for a little bit of gossip. But that's a social cue, too, right?
Deaner, R., Khera, A., & Platt, M. (2005). Monkeys Pay Per View: Adaptive Valuation of Social Images by Rhesus Macaques Current Biology, 15 (6), 543-548 DOI: 10.1016/j.cub.2005.01.044