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This is SCIENCE IN THE NEWS in VOA Special English. I'm Steve Ember.

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And I'm Faith Lapidus. This week -- learn about three separate studies that all involve faces. One has to do with facial blindness -- scientists have found that this disorder is more common than they thought ...

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The second study examines the ability of women to read a man's face ...

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And the third compares the ability of men and women to look at a face and recognize different emotions.

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Some people never forget a face. Some never remember them.

Facial blindness is the inability to recognize the faces of people you have seen in the past or even recently. The scientific name for this condition is prosopagnosia.

Facial blindness can happen in rare cases after a stroke or a brain injury. There is also a genetic form which scientists have considered even rarer.

But a new study suggests that the congenital form of facial blindness is much more common than researchers have believed. And the scientists say the findings provide evidence that this disorder almost always runs in families.

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A team led by researchers at the Institute of Human Genetics at the University of Muenster, in Germany, did the study. They tested almost seven hundred students from local schools. The students answered a series of questions to identify if they had facial blindness.

The researchers found that seventeen students had the condition. Fourteen of those students agreed to have their family members also take part in the study. The researchers found that each one of the fourteen had at least one immediate family member with facial blindness.

The scientists published the first report on how common the disorder is. The report appeared recently in the American Journal of Medical Genetics.

An abnormality in a single gene is believed to cause this condition. The scientists have not yet found the gene.

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Many people with facial blindness recognize close family members. But they can find it difficult to follow along with things like television shows because they do not recognize the actors' faces. In extreme cases, people cannot even recognize their own face in a picture of a group.

Some people with facial blindness avoid social situations. Others use excuses like they need new glasses. No cure is known for facial blindness. People who have it usually develop other methods to recognize people. They pay close attention to other details, like voices, clothing, body shape or the way a person walks.

There is a Web site where you can learn more about facial blindness. The site is operated by research centers at Harvard University in the United States and University College London. The address is faceblind.org.

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You are listening to SCIENCE IN THE NEWS in VOA Special English.

The next study we look at examines the ability of women to tell some things about a man just by looking at him.

This recent study found that a man's face can tell a woman if he is interested in children. The researchers say women are also able to rate the amount of male sex hormone that a man has just by reading his face.

The research took place at the University of Chicago and the University of California, Santa Barbara. The findings appeared in the Proceedings of the Royal Society.

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A group of twenty-nine female students at the California school looked at photographs of men's faces. The young women had to rate what they believed to be the men's interest in children and their manliness. The women also had to rate their own interest in each man. The women were asked if they would be interested in the man as a short-term lover or a long-term partner.

The men in the pictures came from different ethnic backgrounds and were told to have a neutral expression.

Researchers in Chicago used thirty-nine male college students in the study. They tested them to see how much they liked children. The young men looked at pictures of babies and adults and had to say which pictures interested them more. Five showed no interest in the babies. Some showed little or no interest in the adults.

The scientists also tested saliva from the men to measure how much testosterone each man had.

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The researchers compared the results from the women and the men.

The women were able to tell from the photos of the men which ones had high testosterone levels and which ones liked children the most. Twenty of the twenty-nine women correctly identified the men who liked babies. And nineteen of the women correctly identified the men who showed the least interest in children.

So what about when it came to choosing which men appealed most to the women? The study found that the women were more interested in men with high testosterone levels for short-term relationships. The women considered these men to look more masculine.

Earlier research has suggested that a well-defined jaw and thick facial hair are among the signals of high testosterone levels.

The men more likely to be chosen for long-term relationships were those who appeared to like children. The men seen as most interested in children were the same ones who had expressed the most interest in children in the picture test.

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Some people might not find these results all that surprising. But the researchers were surprised at how well women can judge testosterone levels and interest in children. Still, they are not sure what it is exactly about men's faces or their expressions that signal these things to women.

Five female graduate students also looked at the pictures of the men. These women had to rate how happy or angry the men looked. The men who were more interested in babies were more likely to be rated as looking happy.

In any case, the researchers say they found no connection between how much testosterone a man had and how much he liked babies.

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A third recent study looked at the way people recognize emotion in facial expressions. For this study, researchers showed pictures of faces to seventy-eight men and seventy-eight women. Each face expressed one of six emotions. These were anger, fear, disgust, happiness, sadness and surprise.

The researchers asked the study group to identify the different expressions. They also noted the amount of time it took each person to identify the emotion.

The researchers found that anger was the emotion most quickly recognized, a fact that has also been shown in earlier studies. They also found the men were especially quick to identify the faces of angry males. The women were quicker to recognize other expressions, like happiness or sadness.

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The researchers believe their study provides evidence that skills for identifying facial expressions have developed differently in men and women. Men were more likely to face a deadly threat from another man than from a woman. So being able to quickly identify the face of an angry man would have been helpful for survival.

Scientists from the United States and Australia led the study. The findings appeared in Current Biology.

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Finally we have one more study to tell you about. This one involves people who at times become uncontrollably angry. Scientists call it intermittent explosive disorder. They say it is caused by a chemical imbalance in the brain.

Researchers at Harvard Medical School and Massachusetts General Hospital in Boston and at the University of Chicago did the study. They used information from a study of more than nine thousand adults in the United States. They say intermittent explosive disorder is "much more common" than has been recognized. They say it affects as many as seven percent of adults at some point in their lifetimes, depending on how widely it is defined.

Doctors say it is made worse for some by stress from bad drivers, crowded roads and busy lives.

The findings appeared in the Archives of General Psychiatry. More than eighty percent of the people with the disorder also had depression, anxiety or problems with drugs or alcohol. But less than thirty percent were ever treated for their anger. The researchers suggest that early treatment of anger might prevent some of the other disorders.

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SCIENCE IN THE NEWS was written and produced by Brianna Blake. Transcripts and archives of our shows are at WWW.51VOA.COM. I'm Steve Ember.

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And I'm Faith Lapidus. We hope you can join us again next week for more news about science in Special English on the Voice of America.