by Chet Raymo
"Click on the image above to make it as big as you can on your screen. It's pretty, is it not? It is, in fact, an image of something invisibly small, so small and so beyond apprehension by the unaided senses that it can only be represented schematically, in his case as a TinkerToy construction of balls-and-sticks (upper right) and, more abstractly, as a multicolored ribbon (left).
What is it? The stick-and-ball construction is the "cuddle" hormone, oxytocin. 43 carbon atoms, 66 hydrogens, 12 nitrogens, 12 oxygens, and 2 sulfurs: the basic TinkerToy set of organic chemistry. It's all in the way they go together; it's all a matter of shape. The ribbon is the carrier protein neurophysin, that links with oxytocin and carries it from its source in the hypothalamus to receptors. Oxytocin mediates many responses, having to do with sexual arousal, lactation, mother-infant bonding, and so on. It is perhaps best known for promoting bonding between groups of individuals in many animals, including humans. Hence, "the cuddle hormone."
Research reported in an issue of "Science" (June 11, 2010) by Carsten De Dreu of the University of Amsterdam and colleagues confirmed that nasally administered oxytocin does indeed enhance altruism within parochial groups. More surprisingly, it also promoted defense mechanisms against those outside the group. Not just cuddle, but "tend and defend." The study, by the way, involved only male participants; it would be interesting to repeat with female subjects.
It is increasingly apparent that humans have evolved the biochemical basis- including oxytocin- for cooperative behavior within local groups, and for defensive and aggressive behavior toward those outside the group. Which raises the question: How much of what we read in the newspapers is mediated by biochemistry over which we have little or no conscious control? How do we achieve a world of universal harmony when we have hormones kicking around in our brains that had a head start of tens of millions of years? That is to say: How can we get the tend without the defend?”