[Reading Science] Why Do Humans Marry and Have Children Without 'Love'?

University of California Research Team Studies Prairie Dogs Similar to Humans
"Mating and Parenting Seem to Involve Complex Mechanisms Beyond Hormones"

[Asia Economy Reporter Kim Bong-su] Even after being passionately in love and getting married, couples soon become 'show window couples.' Yet, they do not separate and continue to have children and raise a family. Is this simply a matter of responsibility? How can we understand such human behavior? Recently, scientists conducted an interesting animal behavior experiment related to this. They genetically modified prairie voles, known for their social attachment behaviors such as monogamy and offspring rearing similar to humans, so that they could no longer feel 'love.' Nevertheless, the prairie voles still exhibited similar attachment behaviors. This suggests that mating and parenting behaviors in animals may involve complex mechanisms beyond just the 'love' felt through hormones.

A research team from the University of California published these findings on the 27th of last month in the international scientific journal Neuron. The team used gene-editing technology (CRISPR) to remove the oxytocin receptor, which detects the 'love hormone' oxytocin, from the prairie vole (Prairie vole), which primarily inhabits the North American prairie.

Reference photo. Not related to the article.

Prairie voles maintain lifelong monogamous relationships and show devoted family behaviors, such as caring well for offspring even if they are not their own. They are among the few mammals that form social attachment bonds similar to humans. Therefore, scientists have used prairie vole research to understand the biological basis of human social behavior. It has long been believed that the prairie vole’s unique family affection is due to the action of oxytocin. In fact, the amount of oxytocin secreted in the brains of prairie voles is significantly higher than that found in other rodents. When drugs were injected to block oxytocin receptors, preventing prairie voles from sensing oxytocin, their family-affection behaviors ceased. Even in other rodents like mice, mothers deficient in oxytocin failed to nurse their newborns, causing them to starve. In humans, oxytocin secretion increases with more active social relationships and is closely linked to family relationships and reproduction, such as uterine contractions during childbirth and milk production. Therefore, scientists expected that completely removing oxytocin receptors in prairie vole brains would produce behaviors similar to those seen when oxytocin receptors were blocked.

However, genetically modified prairie voles, despite no longer being able to detect oxytocin, continued to maintain monogamous and offspring-rearing behaviors. Mother prairie voles kept nursing their pups even though their milk supply had decreased. There was no evidence that another hormone involved in social attachment (vasopressin) was secreted more to compensate for the lack of oxytocin. Scientists, who have been studying the potential use of oxytocin in treating human social attachment disorders such as autism, are perplexed by these findings.

The research team believes that complex mechanisms beyond oxytocin receptors influence animal behavior, which explains these unexpected results. Professor Devanand Manoli of the University of California said, “It makes sense that behaviors like monogamy and family care can be resilient to the absence of a single protein (oxytocin receptor). Attachment bonds are very important, and it would be stranger if there were only one single link.” There may be other mechanisms that partially compensate for the loss of oxytocin receptors. In natural prairie voles, such mechanisms may exist and activate when oxytocin receptor function is suddenly lost, whereas genetically modified prairie voles lack oxytocin receptors from the start and thus do not have such compensatory mechanisms.

There are also calls for more precise research on the role of oxytocin. Professor Nirao Shah of Stanford University said, “If we are really going to call oxytocin the ‘love hormone,’ more research is definitely needed.”