In his lesser known 1872 book The Expression of Emotions in Man and Animals, Darwin proposed that empathy is a universal trait.
"He saw this book as an important contribution showing the commonality of all people," Ekman said. (Read more about Darwin's scientific legacy.)
It's also possible that Darwin encountered Buddhist teachings through letters from other scholars of the time, he added.
Over the past few years, Ekman examined Darwin's book along with Buddhist teachings and divided compassion into three types: simple, global, and heroic.
Simple compassion is the almost instinctual form that exists mostly between a mother and an infant.
Global compassion appears when people help distant strangers, such as the outpouring of international aid after the 2004 Indian Ocean tsunami.
And heroic compassion occurs when a person is motivated into epic acts of bravery, for instance, jumping into an icy pond to save someone else's life.
In a recent book co-authored with the Dalai Lama, Ekman suggests creating "compassion gyms" that could test a person's level of compassion and even offer exercises to prompt deeper caring for others.
The Dalai Lama, meanwhile, believes that just the sight of unbearable suffering is enough to inspire compassion.
Darwin also argued fervently in his 1872 book that animals and humans share the capacity for emotion, an idea that has been borne out by later research, Ekman noted.
Many great ape studies, for example, show that the animals can place themselves into another's shoes, so to speak. This sensitivity comes from being self-aware, Barbara King, an anthropologist at the College of William and Mary in Virginia, told National Geographic News.
"We wouldn't be human in the ways we are human today if apes were not deeply emotional creatures and deeply social ones," King said. "We are products of our past."
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