When science writer Linda Geddes met fellow science writer Nic Fleming, it was the beginning of a life-changing neuroendocrine experiment. Their interactions and emotional ties became more serious over time, leading to dating and, finally, a marriage proposal. To celebrate their union, they decided that the ceremony would take place in the beautiful countryside of Devon County in England.

Following a flurry of wedding plans, Linda and Nic’s friends and family joined them for their big day. As Linda anticipated walking down the aisle, she felt a mixture of anxiety and excitement. Wearing a beautiful strapless gown, she proceeded past her guests to join her fiancé, who wore a tux with tails. This emotional day was filled with endless traditions and rituals to mark each stage of the wedding. With their friends and family serving as witnesses, they exchanged their vows and then enjoyed a wonderful reception and dinner in a beautiful country house.

Behind the Scenes:

Linda and Nic’s wedding appeared to be a very traditional occasion, similar to many such emotional unions that occur each year. Yet, there was more going on at this picturesque wedding than met the eye. Being science writers, Linda and Nic wanted to do a little experiment on their wedding day. Having read about the hormone oxytocin’s role in love and social bonds, they wondered whether their “love hormones” and those of their guests would increase during the wedding ceremony. They called neuroscientist Paul Zak at Claremont Graduate University and asked if he would collect blood samples from the couple, family, and friends before and after the wedding ceremony. Zak enthusiastically agreed to participate and instructed Linda to locate a refrigerator and other supplies to process the blood onsite at the wedding. Linda took on the task of convincing their friends and family that it wouldn’t be so bad to donate a little blood before and after the “I do’s.” Linda’s childhood friend who was a nurse volunteered to conduct the blood draws, after which the samples were processed and placed on dry ice for the trip back to the United States.

In addition to oxytocin, a few additional neurochemicals were measured in the blood —vasopressin (implicated in social responses such as jealousy and possessiveness), cortisol, and testosterone. What did the results show? Oxytocin levels in the happy couple and their close relatives showed more of an increase during the ceremony than did those of the other guests. Linda, the bride, had the highest oxytocin levels with a 28% increase during the ceremony, followed by her mother, the father of the groom, and (finally!) the groom. The groom’s brother and two other members of the wedding party experienced an increase in oxytocin levels during the ceremony, but the remaining guests and one bridesmaid experienced decreases in oxytocin levels during the ceremony.

Zak and the wedding couple predicted that vasopressin would increase in Nic following the ceremony, as he might feel possessive of his beautiful new bride. However, Nic’s vasopressin levels actually decreased. Not to anyone’s surprise, the stress hormone cortisol was high in the bride before the wedding and increased even further in her post-ceremony blood sample. The groom, however, showed a decrease in cortisol immediately following the ceremony. And, whereas it was predicted that Nic’s testosterone levels would decrease during this bonding ceremony, his results surprised everyone—his plasma testosterone level doubled during the ceremony. He later declared that his mind was not on the upcoming honeymoon, although we suspect otherwise. For now, his testosterone spike will remain a mystery.

Although the heading for this section includes the word “experimental,” this is obviously far from a controlled experiment. It is a combination of a case study and field research, but one with real-world value despite the small number of subjects. Obviously, it is difficult to hold a wedding in the laboratory! Endocrinological, or hormonal, measures are traditionally highly variable with prominent individual differences, so more subjects would be required for more reliable results.

Regardless, this was an interesting case to introduce our investigation of the role of oxytocin, vasopressin, and other hormones—including the reproductive hormones testosterone and estrogen—in social relationships. Extensive research has been conducted to identify the important roles that these hormones play in building social bonds. In this chapter, you’ll read more about the effects of various hormones, especially those involved in affiliative behaviors (behaviors leading to social cohesiveness), such as friendship, and reproductive behaviors, such as sex and parenting.