Yet given her professional background, Dr. Oakley couldn’t help doubting altruism’s exalted reputation. “I’m not looking at altruism as a sacred thing from on high,” she said. “I’m looking at it as an engineer.”

And by the first rule of engineering, she said, “there is no such thing as a free lunch; there are always trade-offs.” If you increase order in one place, you must decrease it somewhere else.

Moreover, the laws of thermodynamics dictate that the transfer of energy will itself exact a tax, which means that the overall disorder churned up by the transaction will be slightly greater than the new orderliness created. None of which is to argue against good deeds, Dr. Oakley said, but rather to adopt a bit of an engineer’s mind-set, and be prepared for energy losses and your own limitations.

Train nurses to be highly empathetic and, yes, their patients will love them. But studies show that empathetic nurses burn out and leave the profession more quickly than do their peers who remain aloof. Give generously to Child A, and Child B will immediately howl foul, while quiet Child C will grow up and write nasty novels about you. “Pathologies of altruism,” as Dr. Oakley put it, “are bound to arise.”

Rachel Bachner-Melman, a clinical psychologist at Hadassah University Medical Center in Jerusalem who specializes in eating disorders, has seen the impact of extreme selflessness on the anorexic young women who populate her ward.

“They are terribly sensitive to the needs of those around them,” she said in an interview. “They know who needs to be pushed in a wheelchair, who needs a word of encouragement, who needs to be fed.”

Yet the spectral empaths will express no desires of their own. “They try to hide their needs or deny their needs or pretend their needs don’t exist,” Dr. Bachner-Melman went on. “They barely feel they have the right to exist themselves.” They apologize for themselves, for the hated, hollow self, by giving, ceaselessly giving.