Answer: In an fMRI brain scan, empathy resembles a sort of minor constellation, with clusters of encephalic stars glowing in the cosmos of an otherwise dark brain, says Lydialyle Gibson in "University of Chicago Magazine." This signature network of cells lights up not only when a subject witnesses someone else in pain but also when the subject experiences pain firsthand, though the constellations are somewhat distinct. "The brain knows the difference, and that is important."

Empathy begins with shared emotion, says neuroscientist Jean Decety, and is hard-wired into our brains. A baby hearing another baby cry will begin to cry too, while people of all ages will unconsciously mimic the facial expressions of those they see. But empathy can be learned as well. The good car salesperson is the one with empathy, as is the good boss, teacher, doctor (the doctor who can feel for you will mysteriously help you feel better). Yet people who lose themselves too much in another's distress may sacrifice their capacity to help.

"In human society, empathy is the glue," says Decety, pulling our separate paths together into shared feeling. Amazingly this ancient glue is now detectable by science.

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Send STRANGE questions to brothers Bill and Rich at strangetrue@compuserve.com, co-authors of "Can a Guy Get Pregnant? Scientific Answers to Everyday (and Not-So- Everyday) Questions," from Pi Press.