August 20, 2004
People With Asymmetric Bodies More Aggressive?

Beware people with uneven body shapes.

Research showed that the farther certain paired body parts were from symmetry – if one ear, index finger or foot was bigger than another, for example – the more likely it is was that a person would show signs of aggression when provoked. The symmetry effects were different in men and women, however.

While the findings may seem strange, there is a plausible explanation, said Zeynep Benderlioglu, co-author of the study and a post-doctoral researcher at Ohio State University.

The physical attraction people have to highly symmetrical faces in the opposite sex is very likely the product of natural selection. The symmetry is a sign of health and reproductive fitness. This latest study shows that asymmetry is even a proxy for a tendency toward impulsiveness.

Body asymmetry is thought to be an indicator that the fetus was under stress (e.g. toxins, nutrient deficiencies or perhaps more stress hormones released by the mother) during development. The visible physical asymmetry is thought to be a proxy for malformations of other less visble parts of the body including the brain.

The study involved 100 college students (51 men and 49 women). Researchers measured differences in size of several paired body parts, including finger length, palm height, wrist diameter, elbow width, ear height and width, foot breadth and ankle circumference. The sum of all the differences in these pairs gave researchers a score of asymmetry for each participant.

The students, who were all volunteers, were told they were going to participate in a study of persuasive ability. They were given a list of phone numbers to call and attempt to raise funds for a fictitious charity organization. But they were actually calling two people involved in the study who were given instructions about how to respond to the study participants.

One of the people the participants called seemed friendly and amenable to giving, but said he didn’t have money to donate. But the second charity target was confrontational. He directly challenged the caller and the worthiness of the donation.

The researchers had rigged the phones so they could measure how hard the participants slammed the receiver down after the call – this was a measure of reactive aggression.

Results showed that, in general, the more asymmetry the participants showed in their body parts, the more force they used when hanging up the phone.

But there were also interesting gender differences.

In men, asymmetry was related to a more aggressive response when ending the phone call under the low-provocation condition – when the person simply didn’t have money to give. But there was no such association between asymmetry and aggression in the high-provocation condition -- when they talked with the rude charity target.

For women, it was just the opposite – there was no relation between asymmetry and aggression with the low-provocation caller, but women with higher asymmetry scores used more force when hanging up from the rude, high-provocation caller.

Benderlioglu said these results probably have to do with the different ways men and women respond to provocation in general.

“Research has shown that men are quicker to anger than are women,” she said. “But while unprovoked men are generally more aggressive than women, the gender differences either disappear under provocation, or women may actually become more aggressive than men.”

High testosterone made men more angry during low-provocation phone calls. But the opposite was the case with women.

Men with high levels of testosterone used more force when slamming down the phone only under the low-provocation condition. In women, higher levels of testosterone were associated with higher aggressiveness only under the high-provocation condition.

One of the most interesting twists is that confrontational behavior does not always elicit an aggressive response. But this makes sense intuitively. In many situations a person who shows fear is more likely to be attacked than a person who acts menacingly.

Update: Also see my related post Premature Birth Produces More Lasting Brain Effects In Boys. Factors that cause less than optimal conditions during pregnancies have the potential of creating behavior problems that will endure for life. Drug abuse, malnutrition, physical abuse of pregnant women, and other stressors on developing fetuses exact a very long term cost to society as a whole.

Share |      Randall Parker, 2004 August 20 04:56 PM  Brain Violence

Fly said at August 20, 2004 6:38 PM:

Interesting post.

Over at GNXP someone commented that the Flynn Effect is likely due to the better health and nutrition of developed countries. He then commented that he didn’t expect to see any further improvement once a country reaches “Developed” status.

I wondered about that second conclusion.

This post is an example of how better parenting could produce a better brain.

In the past you’ve posted on Choline supplements.

Someone at GNXP posted this link to a paper showing Creatine supplementation in vegetarians increased IQ test scores by a standard deviation.

Imagine following:
The best parenting advice. (No smoking, alcohol, or drugs. Proper exercise and rest. Avoid stress.)
The best exercise and diet recommendations.
The best drug or supplement program.
The best lifestyle. (Stay mentally active.)

What would be the combined effect on IQ and memory?

Randall Parker said at August 20, 2004 6:59 PM:


People who are taller, smarter, better looking, and healthier on average already had good fetal development and child development conditions. The effects of better nutrition, reduced exposure to illicit drugs, reduced exposure to the effects of mom getting beaten while pregnant, reduced exposure to sexually transmitted diseases during pregnancy, and assorted other factors would tend to help the lower classes and less bright more than the upper classes and more bright since it is the less able types who are more likely to creating the bad conditions for developing fetuses in the first place.

But how to bring about better parenting? It can't be done without quite a bit of government use of force. Prevent junkies from getting pregnant by either forcibly implanting Norplant or lock them up in institutions while they are pregnant. How to stop men from beating their women? That is already a cottage industry with social workers employed full time on it with a fairly limited amount of success.

Vitamin supplement program? That'd require the women to be responsible enough to take the pills. Some of those who need the pills would be responsible Some wouldn't.

Fly said at August 21, 2004 10:34 AM:

Do intelligent people really know all the ways they could improve their children?
Do intelligent people really know all the ways they could improve their own minds?

Randall, you’ve posted on recent discoveries related to fetal development and nutrition. I doubt many medical doctors are aware of these connections. Certainly most parents aren’t aware.

You posted on the connection between long-term Choline supplementation and memory. I doubt many people are aware of that possible connection.

Until I read that post on Creatine supplementation this week I had no idea Creatine could have such an effect. And I have followed such topics for decades. (That paper claims a standard deviation improvement in IQ. If that result is confirmed it is amazing.)

So what works and what doesn’t.

With brain science advancing so rapidly I expect we will have far better evidence for the effects of optimal nutrition.

Imagine if a standard SAT tutoring program included helpful nutrition and drug advice.

gc said at August 21, 2004 1:58 PM:


Whoa, thanks for bringing that creatine piece to my attention. I'd missed that pickup by Alex B. 15 points!?! That's unbelievable. I remember when I was using creatine that I was in really good shape, and I remember thinking clearly as well - I had assigned that to the rigors of a good exercise/discipline schedule, but perhaps it was biological. Amazing. I think I'll restart supplementation.

Fly said at August 21, 2004 4:36 PM:

GC, I’d be very interested in reading what people on GNXP think of that paper.

More generally I’m interested in a scientific evaluation of all mental supplements or training methods. I know there are many substances that enhance mental performance. It would be nice to have a collection of good science papers that evaluate their effectiveness.

There are many sites online that offer physical training, nutrition, and supplement advice. Is there a comparable site for mental training? (I don’t mean sites that sell junk based on one old rat experiment.)

Joe said at August 21, 2004 10:24 PM:

I know I'd be very interested in an overview of 'mental training' from an unbiased source as well. I find the concept itself facinating, but most of the websites on the topic I've come accross come off as pretty unscientific. Usually just brief mention of studies involving enhancement in the presence of brain damage, and anecdotal evidence. It's really surprising, given the high value westerners place on intelligence, that there seems to be so few studies of enhancement methods out there. I would have thought the creatine study alone should have generated enough interest to see if the effects were due to lower levels of creatine in vegitarians, or if there would be any effect in non-vegitarians as well.

Tj Green said at August 23, 2004 3:06 PM:

One of the reasons we find symmetrical faces/bodies more attractive,is that it shows that there are less errors in the DNA copying process.That the genes control what I find attractive,I find a little disconcerting.Do I/we exist simply to check for genetic errors? When the "y" chromosome(females don`t have a "Y" chromosome,so mutations are left unrepaired) becomes so badly damaged,so that no boys are born,is our species just thrown away? The genes must be unaware of our existance,our reality,yet we are aware of theirs. We can repair the "y" chromosome,so our species is safe for another seven million years.I sometimes wonder if the genes are testing us for intelligence.

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