The evolutionary of roots of “cuddle hormone” oxytocin

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A hormone known as the “cuddle chemical” helps humans to form monogamous bonds, to feel a loving attachment to their kids, and even to produce breast milk. Now, a new report in Science shows that an avian version of that very same hormone also helps birds to stick together as a flock — a sign that of our seemingly unique social bonds must have evolutionary roots shared by other animals.

Researchers at Indiana University, Bloomingdale, studied the role of the neurochemical mesotocin — similar to humans’ oxytocin — in a highly social songbird species, the zebra finch (shown above). When the researchers blocked mesotocin action in the birds, the finches spent less time in groups or with other birds that they knew. When the researchers increased mesotocin in the birds, however, the finches became more social.

There’s one catch: The results only seem to hold for the females, and not for the males. Oxytocin, the neurochemical in humans and other mammals, also seems more important for women than it is for men. It plays a major role in childbearing and maternal attachment, and possibly even in female orgasm. It would seem, the authors write, that similar substances in birds, in fish and in mammals “have influenced social groupings for most of vertebrate history.”