Because we've always known, deep down in our hearts, that this is true, under the headline, "Depth of the Kindness Hormone Appears to Know Some Bounds":
Oxytocin has been described as the hormone of love. This tiny chemical, released from the hypothalamus region of the brain, gives rat mothers the urge to nurse their pups, keeps male prairie voles monogamous and, even more remarkable, makes people trust each other more.
Yes, you knew there had to be a catch. As oxytocin comes into sharper focus, its social radius of action turns out to have definite limits. The love and trust it promotes are not toward the world in general, just toward a person’s in-group. Oxytocin turns out to be the hormone of the clan, not of universal brotherhood. Psychologists trying to specify its role have now concluded it is the agent of ethnocentrism.
A principal author of the new take on oxytocin is Carsten K. W. De Dreu, a psychologist at the University of Amsterdam. Reading the growing literature on the warm and cuddly effects of oxytocin, he decided on evolutionary principles that no one who placed unbounded trust in others could survive. Thus there must be limits on oxytocin’s ability to induce trust, he assumed, and he set out to define them.
In a report published last year in Science, based on experiments in which subjects distributed money, he and colleagues showed that doses of oxytocin made people more likely to favor the in-group at the expense of an out-group. With a new set of experiments in Tuesday’s issue of the Proceedings of the National Academy of Sciences, he has extended his study to ethnic attitudes, using Muslims and Germans as the out-groups for his subjects, Dutch college students.
What does it mean that a chemical basis for ethnocentrism is embedded in the human brain? “In the ancestral environment it was very important for people to detect in others whether they had a long-term commitment to the group,” Dr. De Dreu said. “Ethnocentrism is a very basic part of humans, and it’s not something we can change by education. That doesn’t mean that the negative aspects of it should be taken for granted.”