The Love and Happiness Hormone - Oxytocin
I'm currently doing an excellent Edx course called "The Science of Happiness", which is dedicated to describing the scientific research into positive psychology - what has been shown to make us happy, and what are the biological mechanisms of those findings.
One of the strongest predictors of whether someone will be happy is the value of social connections that they have in their life. In other words, whether people have strong relationships with others, where they are able to share their feelings and emotions, and feel close to others. These findings were first described by Diener and Seligman in 2002 (see this site for more information).
The researchers at the Greater Good Science Centre and others have been looking into some of the biological mechanisms that might underpin this finding. What they and others are finding is that rather than this "survival of the fittest" paradigm that we have all been taught is a result of evolution, where we are all biologically programmed to look after only ourselves, there are actual biological mechanisms and pathways in us that promote pro-social behaviour, such as care-giving and altruism, and monogamous loving relationships.
In this video from the course, one of the instructors, Dr Dacher Keltner, describes one of the hormones that promotes this behaviour - oxytocin.
I think it's absolutely fascinating stuff.
You can find out more about the biology of love and other positive emotions from the same scientists here: https://www.healyourownpain.com/single-post/2017/02/12/The-science-of-compassion-touch-and-communication-of-emotions-through-touch and here: https://www.healyourownpain.com/single-post/2017/02/08/Measuring-Compassion-in-the-Body.