The president of the European Commission appealed for cooperation between the European Union and the United States.

Here is what Jean-Paul Juncker said to U.S. President Donald Trump during their talks in Washington, DC:

"We are close partners – allies, not enemies. We have to work together."

But two new studies show cooperation does not always go the way people might expect.

When cooperation turns selfish

Erol Akçay is an assistant professor of biology at the University of Pennsylvania. He and other researchers have been trying to understand what makes members of a social group cooperative. He noted in an email to VOA that people, animals, plants, and even bacteria help each other.

Akçay and his research team's first finding deals with the kinds of relationships or ties organisms formed. Were these connections with random strangers? Or were they with those related or already known to them, such as with family members or friends of their parents?

Not surprisingly, Akçay learned that groups with many related connections became cooperative. However, as cooperation became more common, he noticed something new: Cooperating individuals also began to help people they were not related to. They helped everyone.

But a few individuals did not give back. As a result, the cooperative nature of the group changed. Everyone began to act selfishly.

Selfish societies were not a goal of Akçay's study. So he tried to find what could bring cooperation back. He looked again at the link between individuals.

Akçay observed that when making a connection seemed costly individuals were more likely to limit their efforts. For example, primates spend more time grooming family members than others in the group. Or, as noted in Science Daily, you and I may go to the trouble of sending a holiday gift to a distant relative, but not to someone we just met on a bus.

As individuals spent time working on their connections with family members and friends, the cooperative nature of the group returned.

And what about those who did not cooperate at all? Akçay wrote in an email that the defectors "pay no cost and provide no benefit."

But they missed something, he noted. If everyone cooperated, they all would have received more in return.

The study was published in the journal Nature Communications.

When good guys finish last

Another study examines how we react to extremely cooperative or generous people. In brief: We don't like those who make us look bad.

The study was a project of researchers at the University of Guelph in Canada. Their findings were reported in the publication Psychological Science.

Pat Barclay, a psychology professor, was the lead researcher. He found that people across cultures enjoy punishing an individual they see as too good. They especially dislike very cooperative people at work or in other competitive situations.

Barclay says that, when faced with a high-performer, others can answer in two ways: "One is to step up your own game. The other is to bring the other person down."

And often, Barclay says, people make the second choice. They claim the high-performer is a hypocrite or question his or her real reasons for being helpful. The goal, he says, is to reduce the social benefit such people earn for their generous acts. It is also to avoid having to do better themselves.

Barclay suggests that one reason may be found in early human history. If one person was an excellent hunter, the others feared he would take control and become their leader, Barclay said. The group wanted to defend their equal status more than reward a really good hunter.

Barclay says he sees a similar situation with activists who urge others to take action to improve the environment or society. Instead of joining the cause, others may choose to continue in their behavior and attack the activist.

I'm Kelly Jean Kelly.

Kelly Jean Kelly wrote this story for VOA Learning English from Washington, D.C. based on reports from Science Daily. George Grow edited the story.

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random - adj. chosen without a particular plan or pattern

defector - n. a good or helpful result or effect

benefit - v. one who causes a weakness or failure

generous - adj. showing kindness and concern for others

step up - v. to do better, make a greater effort, or improve your performance

hypocrite - n. a person who claims or pretends to have certain beliefs about what is right but who behaves in a way that disagrees with those beliefs

status - n. the position or rank of someone or something when compared to others in a society