Covid-19 update: our rehoming centres aren’t open for public browsing, but we’re still rehoming and taking in dogs, with measures in place to keep staff and adopters safe. Find out more about how national Covid-19 restrictions are affecting our rehoming procedures and other activity.

The Science of (Puppy) Love

Dog friendly wedding - Jess and Frankie

The Science of (Puppy) Love

Earlier this month some of the Canine Behaviour and Research department attended a talk by evolutionary anthropologist, Dr Anna Machin. Dr Machin’s research focuses on the psychology, cognition and neurobiology of human social relationships; how individuals maintain their closest relationships and why people might differ in their desire and ability to do this. As part of the team is currently investigating the human-canine animal bond (HCAB), and with its implications to how potential dog owners might choose their dog, or how adopters might build bonds with their pet post-adoption, here we briefly sum up Dr Machin’s talk.

Firstly, Machin described the four key neurochemicals underpinning “love behaviours”, which are oxytocin, dopamine, serotonin and beta endorphins. If you feel closely bonded or attached to your pet then it’s likely these neurochemicals have been involved. These neurochemicals are thought to be responsible for bonding humans (and other mammals) closely. So closely in fact that it can often cause behavioural synchronicity and the more recently established physiological synchronisation of aligning heart rates, body temperatures, and neurochemical levels (baseline levels of oxytocin). Gamma wave activity in the brain can also start to align and this, Dr Machin refers to as “biobehavioural synchronisation”, suggesting that high levels are found in healthy relationships and highlighting their association with longevity.

But it’s not that simple, we are all unique (both dog and human), not only do we each have a unique set of DNA which codes for various amounts of these neurochemicals to be made and function, but we also each have had our own personal experiences and learning opportunities that make up our very unique love “style” - and that’s even before trying to match it with someone else’s! Research has investigated the oxytocin receptor gene, which turns out – is highly polymorphic (ie comes in lots of forms). The form it takes can influence our motivation for pair bonding, attachment, self-disclosure (important in influencing a bond), and empathy amongst other things. And that’s just one gene!

Ever wonder why you seem to take break ups harder than other people? There’s a (polymorphic variant of a) gene for that! Studies suggest 2% of the population feel romantic rejections more keenly than others thanks to a function variant in their opioid receptor gene.

Similarly, researchers in Beijing found a supposed “singleton” gene during a study of single women. It was suggested that women with a certain version of the 5-HTA1 serotonin gene were more likely to be single than those with an alternative version because it had an impact to the levels of serotonin in their brain (the same serotonin, which is linked to pair-bonding and love). However, as Machin pointed out it may also relate to those with the gene getting less of a serotonin “buzz” from finding love, and less of a buzz = less motivation to carry out that behaviour.

Equally the impact that different environmental factors can have on different genes (the phenomena that is epigenetics) can affect relationships. Dr Machin discussed her research discovery that high levels of stress can cause higher levels of methylation of oxytocin receptor genes (the same oxytocin that can help form bonds). This can alter the expression of the genes, which is then capable of being inherited! To put it another way - your great-grandad’s early life experiences might play a tiny part in your dating life! Wow, huh?

Although not romantic or sexual love, the bonds and close attachments we form with our pets in these ways can play an important role in our lives and vice versa. “Broken” bonds or the failure to create a bond are often cited as a leading risk factor for dogs being abandoned or relinquished into rehoming shelters. The more we can find out about the HCAB and how to support it, the greater the potential benefit for rehoming success. For more information on Dogs Trust HCAB research topic click here.

Don't forget to follow our Twitter account @DTScholars for updates on our work, new blog posts, dog photos, and more!


Dunbar RIM. and Machin AJ., (2014), Journal of Evolutionary Psychology, 12, 109 – 133

Liu, J., Gong, P., & Zhou, X. (2014). The association between romantic relationship status and 5-HT1A gene in young adults. Scientific reports4(1), 1-3.

Machin AJ. and Dunbar RIM., (2011), Behaviour, 148, 985 – 1025

Machin, A. J. & Dunbar, R. I. M. (2013). Sex and Gender as Factors in Romantic Partnerships and Best Friendships Journal of Relationships Research 4:e8.

Machin, A. J. & Dunbar, R. I. M. (2014). The brain opioid theory of social attachment: a review of the evidence in R.I.M. Dunbar, C. Gamble & J.A.J. Gowlett (eds.) Lucy to Language: Benchmark Papers Oxford University Press, Oxford pp.181-213.

Machin, A. J. & Dunbar, R. I. M. (2015). Is kinship a schema? Exploring the evolutionary origins of kinship Adaptive Human Behavior and Physiology 36

Machin, A. (2020, January 21st) The Science of Love. Presentation, London UK.

Marston, L. C., & Bennett, P. C. (2003). Reforging the bond—towards successful canine adoption. Applied Animal Behaviour Science83(3), 227-245.

Nummenmaa, L., Tuominen, L., Dunbar, R., Hirvonen, J., Manninen, S., Helin S., Machin, A., Hari, R., Jääskeläinen, I. P. & Sams, M. (2016). Reinforcing Social Bonds by Touching Modulates Endogenous µ-opioid System Activity in Humans NeuroImage 138:242-7.

Pearce, E. Woldorski, R. Machin, A. & Dunbar, RIM (2017). Variation in the beta-endorphin, oxytocin and dopamine receptor genes associated with different dimensions of human sociality. Proceedings of the National Academy of Sciences, USA 

Way, B. M., Taylor, S. E., & Eisenberger, N. I. (2009). Variation in the μ-opioid receptor gene (OPRM1) is associated with dispositional and neural sensitivity to social rejection. Proceedings of the National Academy of Sciences, 106(35), 15079-15084.