Science: Human Behavior

Washington Post staff writer Shankar Vedantam was online Monday, Aug. 7 at 2 p.m. ET to discuss his weekly series of stories about the sociology and psychology behind news events.

Today's story focuses on the link between hot weather and crime .

Read his past articles, including last week's story about what brain imaging shows about partisan behavior here: Dispatch From the Department of Human Behavior .

A transcript follows .

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Shankar Vedantam: Welcome to the science online chat. We're going to be talking about a couple of my stories today. One story in the paper today talks about how, beyond a certain temperature, hot weather causes violent crime to go down, rather than up. The other story, from last Monday, used brain imaging studies of Democrats and Republicans to show that, rather than weighing all the evidence and coming to a conclusion, partisans often come to a conclusion and then weigh what evidence they need to support that position.

Both these stories are for a weekly series that explores ideas behind the news. If you have recently seen something that intrigued you, speak up and let's chat about it. It could become the subject of a future column!

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Silver Spring, Md.: Shankar -

Ray Bradbury wrote a short story about this phenomenon in the 1950s. I don't remember the name of the story at the moment. A character in the story postulates that 92 degrees is the ideal temperature for violence - hot enough to spark violent activity in response to stress, but not so hot that the person becomes lethargic.

Shankar Vedantam: Thanks for this, Silver Spring. I like Ray Bradbury very much. Don't remember the specific story, though. One interesting thing I couldn't get to in the story today is at what temperature point you start to see this inflection, where violent crime stops going up and starts going down. Turns out, it depends where you are. People from the DC are have gotten used to a certain temperature, so if you take them on a very hot day and plonk them in a very temperate area, you may well unleash the hidden beast. Thankfully, no one has conducted that experiment. (The flip side, of course, is to take violent Washingtonians to Florida, where we can hope the heat will knock them out!)

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Arlington, Va.: Is the same true for cold weather? It seems like the incentive would also be taken away in severely cold weather. Crime rates among Eskimos? In Siberia?

Shankar Vedantam: Excellent question. I have no idea whether people have done such a study. My sense is that the cold tends to predispose people to withdraw (they certainly stay indoors a lot more) so that should have a negative effect on crime. But it is also true that people can drink a lot of alcohol to compensate for it being freezing, and alcohol clearly increases the risk of violence. Interestingly, alcohol has a similar effect on aggression -- it raises it up to a point, but then when people pass out, they are docile as lambs!

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Fairfax, Va.: Neat story. What about the early racial theorists who believed that one's disposition was determined by the climate of one's geographical origin(s)? This was the foundation for many of the racist theories that propped up colonialism in Africa, the southern Americas, etc. The "laziness", "promiscuity", and all other manners of "evil" of the peoples of sub-saharan Africa (as perceived by Europeans) was thought to have been caused by hot weather.

Shankar Vedantam: I agree with you. I hinted at some of this history that tried to compare people in hot countries from those in cold countries. One of the reasons modern statistical methods are so useful is that they can help put such beliefs to the test. Human behavior turns out to be more similar than dissimilar in different places.

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Laurel, Md.: Have you taken a look at the field of evolutionary psychology?

Shankar Vedantam: Hello Laurel. Say more. Yes, I am familiar with some of the work in evolutionary psychology. Did you have something in particular that you wanted to talk about?

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Rockville, Md.: Besides studies on crime and heat, are there other behaviors we humans do more or less of in these hot conditions. Also, what kind of factor does humidity play?

Shankar Vedantam: If you are asking about the sort of stuff we tend not to write about in a family newspaper, well, this is still a family newspaper website! The article today focused only on the question of aggression and temperature.

The humidity question is very interesting. Contrary to their expectations (and mine!) they found that the correlation between temperature and humidity was negative. In other words, the lower the humidity the higher the risk of violent crime. I am not sure whether this is because at very high humidity -- 100 percent -- criminals are deterred by precipitation. That would not explain why you see reduced violence all the way up to 100 percent of course.

The negative relationship between violence and humidity was seen in analyses in Minneapolis and Dallas. Those seem like fairly different weather locales; of course, you might find something quite different if you look at a swampy area.

I suppose one way to look at it is that your discomfort with the humidity rises, you are likely to see less crime! Another reason to enjoy DC's summer discomfort?

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Bradbury story: I don't remember the Bradbury story name either, but I'm pretty sure it was in The October Country anthology. One of my favorites from Ray.

Shankar Vedantam: Posting as followup to earlier conversation ...

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Alexandria, Va.: I found the article on insults particularly interesting--and that in more individualistic countries, family insults may carry less weight. What did the study find as the most common type of insult in the States?

washingtonpost.com: A World of Insults, a World of Reactions

Shankar Vedantam: This question refers to a story a few Mondays ago that explored the sociology of insults, following the Zidane head-butting incident in the World Cup. It found that insults around the world varied depending on whether cultures were individualistic or not; in cultures where family ties were particularly important, the most potent insults seem to be those targeted at family members. At least one psychologist raised the possibility that an insult against Zidane's family, especially given his cultural roots in Arab culture, may have been perceived quite differently than if Zidane's background had been a very individualistic culture.

As for the question about the US, it is a very large country with a lot of different cultures. The story reported that adolescent northerners were less likely to be deeply hurt by insults than adolescent southerners, which speaks to the other factor driving insults -- the greater the masculinity in a certain area, the more the men from that area will trade in insults.

Curiously, and sadly, insults directed at family all over the world focus on women: You will find endless insults about wives and sisters and mothers, but almost nothing about brothers and husbands and fathers.

As for specific insults in the US, I think it would be fair to say they will be about the individual -- the US is among the most individualistic countries in the world.

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Jensen Beach, Fla.: Looking at your inverted "U" in relation to violence, or just plain squirrely behavior, have you ever factored in the heat, time of day, AND a full moon?

Shankar Vedantam: There is a lot of research on other factors besides temperature, but I think you are asking what happens when you combine a lot of different factors that trigger aggression. Obviously, the answer is you get your average Hollywood B movie!

Seriously, as a science writer I have to admit to some skepticism about this, but there is actually some data showing connections between the phases of the moon and violence. Caveat Emptor!

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Washington, D.C.: The partisan study tangibly proves a common sense notion: people can be very close minded! And any additional information is processed through their lens. This may be a bizarre question, but are there known brain chemicals that make people more flexible/open-minded? Kind of like serotonin and sleep or melatonin and happiness?

washingtonpost.com: How the Brain Helps Partisans Admit No Gray

Shankar Vedantam: Thanks. Stories the last two mondays explored the nature of the partisan mind. When Democrats and Republicans are showed candidates they oppose, they have a negative reaction, which is not at all surprising. What is interesting is their brains also seem to turn up the dial on distaste, effectively preventing them from taking in information that would threaten their pre-existing beliefs. When they were shown news items about candidates doing something unpleasant or inconsistent, partisans were quick to spot hypocrisy, but only in the opposing candidate. For their own candidate, the hypocrisy did trigger a negative reaction, but then their brains quickly turned down the dial on the distaste.

I don't know of any specific chemicals that could lead to more open-mindedness. I would also question the need for such chemicals. Being partisan is not a disorder, and there are probably sound evolutionary reasons people are so good at defending their own opinions. Also, don't you mean melatonin-sleep and serotonin-happiness, and not the other way around?

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Chatham, Mass.: I don't believe what you said in your article. It goes against everything I believe in -- I think people are fundamentally fair and want to listen to both sides.

Shankar Vedantam: Well, say more. The data seem pretty clear, and my own perceptions of public discourse tells me that people tend to defend their opinions -- especially when it comes to national politics or the middle east conflict etc -- pretty strongly.

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Lantana, Fla: Can you correct me on the whole 'full moon' issue - the fact that before gas or electrical lighting, people would get in more 'trouble' during full moons since they could see better at night? (I sound whacko, don't I?)

Shankar Vedantam: Hmm. Although wouldn't you say that if you could be seen at night you would be less likely to get up to bad stuff?

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Washington, D.C.: I don't particularly enjoy the recent shift towards fluffier (pop-psychology and sociology) science writing in the Post. The article on the unreasonableness of political partisans was particularly unwelcome---it seemed almost bent to present a scientific defense for the news media coverage that infuriates both the left and right. (Alternate hypothesis: it's just bad journalism that gets partisan blood boiling.) Whatever happened to the important news in physics, biology, chemistry, geology and anthropology, which used to be the beat of writers like Kathy Sawyer?

Shankar Vedantam: Thanks for the comment. The Post does lots of the kind of writing you say is missing. I wrote a story a couple of weeks ago, for example, that explained how scientists were finding that the human genome is undergoing dramatic changes. Kathy Sawyer was certainly irreplaceable, but I think you may be under-counting what some very talented science writers at the Post are doing.

On the specific question about stories related to psychology and sociology, I see no contradiction whatever in being interesting and being scientifically rigorous. I draw my material almost exclusively from the peer reviewed literature. On the partisan story, I fear you may have missed the point of it. There is absolutely no question that media reports can be flawed, or biased. But the experiments examined something else altogether, which is the perception of bias. The fact that pro Israeli and pro Arab partisans can look at the very same clips and come to diametrically opposing conclusion about media bias does tell you something very very interesting about how people watch and read the news.

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Shankar Vedantam: That's all we have time for today. Thanks for the comments and questions!

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