"How do I love thee? Let me count the ways.
I love thee to the depth and breadth and height my soul can reach..."
Exploring the regions of love and passion tends to be the province of songwriters, dramatists and poets like Elizabeth Browning. But researchers at UC Davis are showing that it is possible to count the ways... with more than just words.
Psychologists William Mason, Sally Mendoza and their colleagues are investigating the ties that bind in a small, South American primate known as the titi monkey (pronounced tee-tee), one of the species living at the California Regional Primate Research Center here at UCD.
The titi monkey could be the poster child for picture perfect monogamy. In both the wild and captivity the members of a pair are rarely more than a few yards apart, and do everything together - feed, travel, rest. When titi lovers hang out, they typically sit against each other with their tails intertwined into one long braid. With this intimacy comes emotional dependence. When spouses are separated into different enclosures for a short time (about an hour), they become clearly upset, as measured by their distress calls and agitation. Furthermore, both members of a pair are actively hostile to strangers. It is likely that in the wild, titi monkeys marry until death do them part.
Mason and Mendoza and their colleagues have found that titis pair bond is not just skin deep. There s a chemistry underlying their behavior. For example, levels of the stress hormone, cortisol (also present in humans), increase in the bloodstream when pairmates are separated. In contrast, the presence of a mate has a soothing influence and prevents the rise of cortisol in otherwise stressful situations, such as being moved to another cage.
Is there a limit to the number of intense attachments an animal can form? If titi spouses love each other, how do they feel about their infants? Apparently not much, is the answer. This is not to say that they are bad parents. The mother and father both tend their infant: the father carries it on his back, and the mother nurses it. But while titi parents may be competent, they could not be called loving. If the baby is removed, neither parent acts upset or shows any hormonal changes. When given a choice of who to be with, titis will almost always choose their mate over their infant. In fact, it appears that titi parents cannot distinguish their own infants from a strange one.
In a titi family, closeness between parent and child is up to the child. A titi infant develops a deep attachment not to the mother, the animal that only feeds it, but to its father, the animal with whom it shares contact.
Titis are highly unusual monkeys. A more common attachment scenario is found in squirrel monkeys, another South American primate living at the Primate Center. In this species, mothers and their infants develop deep, mutual bonds, similar to those between titi mates. Unlike titis, however, squirrel monkeys, who live, not as pairs but in large multi-male, multi-female groups, do not have such close bonds with other adults. Although they form friendly social ties with certain other monkeys, these lack the same intensity and underlying chemistry of true attachment.
It is likely that the different bonds formed by titis and squirrel monkeys relate to differences in their social systems. In the large, fast-paced social groups of squirrel monkeys with many females and many infants, a mutual attachment between mother and baby is the surest way for both to keep together, and thus the surest way for the infant to be protected, fed, and so on. For titis, an infant is never going to be around any adults except its own parents. As long as the mother and father are bonded to each other and the infant is attached to one of them, then the infant will be cared for.
This research suggests that intense emotional attachments in humans
probably also have underlying physiological bases, and have been
shaped by social and biological forces during our evolution. The
work also highlights the importance of studying a problem in more
than just one or two species. If the Primate Center at UC Davis
did not house monogamous titis, as well as the more common group-living
primates, we would never have known that two adult monkeys could
care so much about each other, to the depth and breadth and height
of their souls.
Dept. of Anthropology, University of California, Davis, CA 95616.
e-mail: kjstewart@ucdavis.edu