Compassion literally means “to suffer together.” Among emotion researchers, it is defined as the feeling that arises when you are confronted with another’s suffering and feel motivated to relieve that suffering.

Compassion is not the same as empathy or altruism, though the concepts are related. While empathy refers more generally to our ability to take the perspective of and feel the emotions of another person, compassion is when those feelings and thoughts include the desire to help. Altruism, in turn, is the kind, selfless behavior often prompted by feelings of compassion, though one can feel compassion without acting on it, and altruism isn’t always motivated by compassion.

While cynics may dismiss compassion as touchy-feely or irrational, scientists have started to map the biological basis of compassion, suggesting its deep evolutionary purpose. This research has shown that when we feel compassion, our heart rate slows down, we secrete the “bonding hormone” oxytocin, and regions of the brain linked to empathy, caregiving, and feelings of pleasure light up, which often results in our wanting to approach and care for other people.

For more: Learn about self-compassion and compassion fatigue. Read Dacher Keltner’s essay on “The Compassionate Instinct” and Paul Ekman’s “Taxonomy of Compassion,” which reviews different types of compassion.