(USA TODAY) -- College students today show less empathy toward others compared with college students in decades before, a study from the University of Michigan says.

Sara Konrath, a researcher at the university's Institute for Social Research, looked at 72 studies that gauged empathy among 14,000 college students in the past 30 years. She found that empathy has been declining -- especially since 2000.

The research finds that college students today show 40% less empathy vs. students in the 1980s and 1990s. The students are less likely to agree with statements such as "I often have tender, concerned feelings for people less fortunate than me" and "I sometimes try to understand my friends better by imagining how things look from their perspective."

The study did not evaluate why students are less empathetic, but Konrath says one reason may be that people are having fewer face-to-face interactions, communicating instead through social media such as Facebook and Twitter.

"Empathy is best activated when you can see another person's signal for help," Konrath says.

Michigan graduate student Edward O'Brian, who helped collect data for the study, says the "explosion" in social networking has caused college students to spend less time with each other.

"You might spend your night posting on Facebook walls and sending out tweets to hundreds of your online friends, but by doing so, you're also not spending time with real people and gaining valuable interpersonal experiences," O'Brian says.

Another cause may be changing expectations about success. Since the 1980s, there has been a steady trend in people feeling more stressed about trying to "get ahead," Konrath says.

"With so much time and effort devoted to yourself so you can succeed, who has time for others?" O'Brian says.

And this doesn't apply only to college students. With different demands at work -- hours answering and writing e-mail -- people have less time to care about others, Konrath says.

If people are less empathic, she says, it has implications for America's aging population, because older people will increasingly rely on younger generations for support and care.

"Empathy is a very important moral trait in terms of everyday caring for people in our environment," she says.

Claire Raines, author of The Art of Connecting and an expert on generations, says such a study focusing on college students leads to stereotypes of the Millennial generation -- people born between 1980 and 2000 -- as more narcissistic and materialistic, which Raines says isn't necessarily true. She notes that the Millennial generation volunteers more than twice as often as Generation X, or people born roughly between 1960 and 1980. They also have better relationships with their parents, she says.

Raines says that empathy is declining in all generations and that people may be closing themselves off from others in response to the increase in the flow of information and bad news.

"If we just open our hearts to all the misfortune around us, it would be just overwhelming," she says.

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