A mother and her child, a married couple, close friendships, they all have one thing in common. These pairs of individuals have a rich fondness for each other, a bond that is not easily severed. What facilitates relationships like this? Evolutionarily speaking, such kinships are enabled by developments in the mammalian brain. Or rather, they’re caused by love.

Love is a fickle and complex emotion. It is remarkably enigmatic in some ways, yet surprisingly well understood in others. This affectionate emotion, like other ones, is regulated through the expression of chemical and hormonal signals within the brain and body. One of the key chemicals involved in these interactions is oxytocin, which acts on the oxytocin receptor.

After having been discovered in the early 1900s, oxytocin has been studied extensively. It, among other neurochemicals, are believed to be responsible for the advancement and enrichment of interpersonal relationships in humans and other mammals alike. Surprisingly, not all animals may have the capacity to feel and experience intense love.

In 1998, psychoneuroendocrinology researcher Porges outlined a rough path of progression into modern day social groups and pairs through observations of various species’ nervous systems. The first of these progressions dealt with the most basic of survival needs. This included sensations such as hunger, and the subconscious action of digestion.

Following this most primal of minds, Porges found that systems linked to the “reptilian brain” were the second iteration. This second stage of progression is linked to the modulation of “fight or flight” type behaviors. It controls an organism’s ability to perceive threats, and determine a course of action.

The third, most recent of these evolutionary progressions is the mammalian brain. The development of these neural pathways enabled animals to form more structured and interdependent relationships with one another. It also introduced the sensation of love, the ability to form deep and lasting bonds with other organisms.

Oxytocin is deeply connected to the ability to form relationships and maintain friendships. It is speculated that the development of oxytocin and its ensuing effects are what prompted the rise of human civilization. A study in 2011 on the effects of oxytocin found evidence pointing towards this. It found that oxytocin played a role in establishing group identities, leading to tightly knit social groups.

There is also evidence that oxytocin may promote bonding between separate mammalian species. The presence of this “love drug” might be the mechanism behind the affection felt between pets and owners. A 2003 study linked enjoyable human and animal contact to heightened oxytocin levels.


[1] https://www.ncbi.nlm.nih.gov/pubmed/9924740

[2] https://physoc.onlinelibrary.wiley.com/doi/abs/10.1113/jphysiol.1906.sp001148

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3029708/

[4] https://www.sciencedirect.com/science/article/pii/S109002330200237X?via%3Dihub



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