It’s True, Your Shit Doesn’t Stink, And You Can Thank Evolution For It

Fine, your shit probably does objectively stink, but because you know you’re less likely to catch an unfamiliar disease from it, it disgusts you less. Here’s the abstract from a forthcoming paper by Ming Peng, Lei Chang, and Renlai Zhou that supports an evolutionary explanation for the “source effect.”

Known as the source effect, feelings of disgust have been found to differ depending on the source of the disgusting material, with that emanating from oneself and familiar others eliciting less disgust than that of strangers. We tested the source effect on self-report of disgust feelings (Study 1), physiological response in heart rate (Study 2), and behavioral response in terms of approach–avoidance movement (Study 3). The results showed significantly higher levels of disgust feelings, more reduced heart rates, and faster avoidance behavior when processing disgusting material associated with strangers compared to that of familiar persons. Together these findings support the evolutionary view that disgust, as part of the human behavioral immune system to drive avoidance from disease-carrying agents, will likely be activated more intensely and quickly in response to unfamiliar as compared to familiar conspecifics who carry common germs more defendable by our shared physical immunity.

Now you’ll think twice next time you want to make fun of a dog for sniffing another dog’s poop.

Why Do We Experience Mental States?

While mental states are generally thought to be involved in causing behavior, it is not clear why they are useful for this purpose. Would it not be possible for selection to design people so that, like biological automatons, they adaptively responded to stimuli without experiencing mental states (Dennett, 1991)?


All organisms were faced with problems in their evolutionary past in which they had to choose a response. For some problems, the type of response that maximized fitness depended heavily on subtle variations in context; for other problems, the best response was much less dependent upon subtle variations. However, there is no way to design a nervous system that simply calculates the fitness consequences of different actions to determine the option that maximizes reproduction (Symons, 1992; Tooby & Cosmides, 1990).

Still, the organism must have a nervous system that allows it to make good choices. Selection could imbue the nervous system with a suite of hard-wired response rules, each tailored to a particular context. If the organism is merely a collection of hard-wired rules, it will respond to environmental stimuli without necessarily experiencing mental states. However, hard-wired solutions are less tenable for problems in which the optimal response varies dramatically with subtle changes in context. To deal with a nearly infinite number of subtly varying contexts that could be encountered, the biological automaton must come equipped with a nearly infinite number of hard-wired rules, each of which is invoked in a slightly different context.

Alternatively, selection could design a nervous system that allows the organism, before
making a choice, to internally simulate the likely outcomes of behavioral options and predict which ones best satisfy internal goals (Alexander, 1989). Presumably, internal simulation would be less cumbersome than storing a large number of hard-wired rules and more efficient than post hoc learning. It would require the ability to internally represent the self and the external environment, including other actors if their behaviors must be simulated. Since actors have goals, internal simulation would also require representation of the motivational systems of the actors in the simulation. The organism must then make behavioral decisions on the basis of the outcomes of the internal simulation, which will require some internal standard of utility for identifying and comparing desirable and undesirable outcomes (e.g., aesthetic experience). In short, mental states (such as perceptions, beliefs, emotions, intentions, etc.) may allow an organism to identify a behavioral option (from a large suite of options) that approximates an optimal solution to a problem posed by the environment.

That’s Paul Andrews in an old Evolution and Human Behavior paper.

The Quest For the “Lipstick Effect”

In every economic downturn some intrepid journalist pens a story about the “Lipstick Effect” — the tendency for women to buy more beauty products when the economy is in bad shape. In theory, the behavior is driven by evolutionary concerns. With fewer men able to offer the security of financial stability, women must enhance their beauty in order to deal with the increased competition.

Although economic data provides some support for the Lipstick Effect, there has never been any experimental evidence that demonstrates its existence or explains why it arises. Nevertheless, a group of researchers led by Sarah Hill and Christopher Rodeheffer of TCU decided to put on their Indiana Jones hats and attempt to prove to the world once and for all that the Lipstick Effect is real.

The researchers began by having subjects read articles that were either about the recent economic downturn or architectural design. They then asked subjects to rate how much they desired certain beauty-related or non-beauty related products. Those who read about the recession had a decreased desire to purchase non-beauty products, regardless of whether they were male or female. However, while men also had less desire to purchase beauty-related products, women had an increased desire to purchased beauty-related products.

A follow up experiment found that the female desire for beauty products was mediated by their desire for financial security in a relationship partner, and a third experiment ruled out the possibility that the beauty products were only desired because they were inexpensive. In a final experiment, subjects primed to think about the bad economy were more likely to choose one of two identical products if its advertising slogan focused on attracting a mate.

One interesting question that remains is whether the female response would be different if the cultural circumstances were different. What if there’s a gun shortage in a country rife with violence? Would the same kind of lipstick effect emerge? Or what if there’s a recession in a small country where it’s much more common for people to move away. If women are driven by evolutionary concerns is it possible that an increased number of women will leave the country in search of a financially secure man?

As the researchers point out, there are also bound to be things that men do in response to recessions. Because fewer men are able to offer financial security, finding a way to signal that you’re one of those men has tremendous rewards. Could there be a “Create a Republican SuperPAC Effect” where men attempt to show they’re wealthy by raising money to attack progressive politicians? Only time will tell, but for now those who love the three pillars of American society — sex, the feeling of economic inadequacy, and consumerism — can rest easy knowing the Lipstick effect is alive and well.
Hill, S., Rodeheffer, C., Griskevicius, V., Durante, K., & White, A. (2012). Boosting Beauty in an Economic Decline: Mating, Spending, and the Lipstick Effect. Journal of Personality and Social Psychology DOI: 10.1037/a0028657

When Your Brain Keeps You From Doing the Right Thing (Or, Why I’m Not Batman)

There are certain occasions when the world provides a perfect opportunity to examine human psychology through the window of your own brain.  A few days ago I managed to find myself in such a situation. Here’s what happened:

I was walking with some friends down a relatively busy D.C. street lined with shops and restaurants. About half a block ahead there was a small crowd of people. As we approached we saw that about 30 feet beyond the crowd there was an inebriated, mentally unstable homeless man verbally berating another man and engaging in what I would call physically aggressive behavior (not quite assault). It was hard to tell exactly what was going on, but at first glance it looked like a run-of-the-mill fight between two people.

We stopped at the crowd of  around 10 people and surveyed the situation for a few seconds. At that point the attacker violently pushed the victim to the ground. The victim remained on the ground and the attacker continued yelling nonsensical insults at him.

Now I don’t tend to be a very courageous person, but years of watching drunk people yell and fight at bars and concerts has left me with little tolerance for physical fighting. It’s the only time I’m ready to be a vigilante. Usually if I’m at a bar and two people appear close to fighting I’ll go near them and yell something like “Why don’t you use indoor voices to work this out!” Once in a blue moon I’ll physically get between them.

So I decided to start walking aggressively toward the two men. I wasn’t sure what I was going to do. Ideally, I thought I could reason with the attacker and convince him violence was bad.  Practically, I was hoping to scare the attacker off.

When I got about 10 feet away I stopped.  I wasn’t sure why. I stared daggers at the attacker, but I didn’t move any closer. He continued yelling. A few seconds later another bystander came forward and helped pull the victim away. At this point the attacker began to back off.  The police arrived seconds later and took him away.  The victim escaped with nothing more than a few scrapes.

In the minutes that followed I couldn’t stop wondering why I stopped. The simple explanation is that at the exact moment I approached the scene the attacker was merely yelling. On some level I might have been worried that my presence would incite him to get violent. But that reasoning didn’t completely satisfy me. Eventually, I decided on the following explanation:

Although the attacker being was verbally and physically abusive, there was no reason the man being attacked could not run away. The attacker was not continuously assaulting the victim or restricting his movement in any way. In fact, the attacker held a crutch in one hand. Yet the man just lay on the ground. He didn’t move. Clearly he was afraid, and as a result it seems he resorted to a kind of “stay in fetal position” defense.

I think it was the victim’s lack of movement that stopped me.  In fast moving and potentially dangerous situations our unconscious picks up on a lot of cues. I think I picked up on the fact that the victim was not running away, and that flashed huge warning sign in my head. The attacker must have some other power or weapon. Maybe he has a gun? Maybe a knife? Why wouldn’t the victim just get up? I wasn’t consciously aware of these thoughts, but I think they were there, and their presence was enough to make me pause for just a few seconds.

The situation shows just how hard it is to help others in these types of situations. Although I didn’t do the “right thing” for society, I did do the right thing for me. There was a potentially dangerous situation, and my brain ensured that I didn’t put myself in danger.  From an evolutionary standpoint it was a success. From the standpoint of the victim (or my ego), it was not.

Why We Laugh

Wired has a nice profile on Peter McGraw, a UC-Boulder professor who is one of the world’s leading researchers on the psychology of humor.  McGraw’s grand theory is based on the idea of “benign violations.” It holds that comedy results when the violation of something (social norms, moral norms, personal dignity, etc.) is perceived to not be a threat. Like most things, it’s all evolutionary:

McGraw believes that laughter developed as an instinctual way to signal that a threat is actually a false alarm—say, that a rustle in the bushes is the wind, not a saber-toothed tiger. “Organisms that could separate benign violations from real threats benefited greatly,” McGraw says.

The evolutionary account also explains why we enjoy comedy so much. McGraw’s notion of a violation occurs whenever our predictions are proven to be inaccurate.  If the consequence of a bad prediction is venturing into a bush filled with saber-tooth tigers, that makes bad predictions very problematic.  The result is that realizing the consequences of a predictive failure are benign leads an intense influx of positive affect.

McGraw’s blog is here.