While love is complicated and can’t simply be reduced to three biological brain states, there are clear neurochemical processes that do contribute to feelings of love. While not called ‘love’, the desire to mate with a specific individual is not limited to humans, but exists across many species. The drive to find a mate, bond, and reproduce is called the ‘attraction system’. This system is made up of three fundamental pathways — lust, attraction and attachment – which occur in both birds and mammals (including humans).1
1. Lust
Is sex really all that guys think about? Possibly. But women think about it too. Lust is our sex drive or libido and it is in part driven by the hormones testosterone and estrogen. Lust refers to an urge or desire that motivates us to partake in sexual activity. This desire to be involved in sexual activity is there regardless of whether someone has a sexual partner or not.
2. Attraction
Despite sex being ‘all that we think about’, we do seek and pursue specific partners. And this is common across species.
“I thought that [he] would have chosen a more comely female but …He couldn’t take his eyes off her. He didn’t even bother to eat, so enthralled was he by her balding charms” (from Gladikas, 1995)2 [‘He’ is an orangutan in this passage.]
“It was evidently a case of love at first sight, for she swam about the new-comer caressingly…with overtures of affection” (Darwin, 1871)3 [‘She’ is a mallard duck.]
Although often described as part of lust, attraction is distinguished from lust because it involves focusing our attention to a particular person or desire. Lust on the other hand is our libido; it is the underlying urge for sexual gratification. Attraction is also in part driven by different hormones than is lust, with adrenaline, dopamine and serotonin playing key roles. Ultimately, engaging in sexual activity may be just as dependent upon individual attraction as it is upon lust.4
3. Attachment
Attachment promotes the likelihood that two individuals will stay together to complete parenting duties. In birds and mammals evidence of an attachment bond is observed when ‘couples’ engage in mutual tasks such as territory defense, nest building, feeding and parental chores.
Lust has a different mechanism than attachment because the desire for lust is ubiquitous but the formation of a long-term attachment to a mating partner is much less common across species. The hormones identified to help drive attachment, oxytocin and vasopressin, are again different than the hormones involved in lust and attraction.
Love, it’s complicated
While these three interrelated brain systems contribute to our feelings of love, they can also act independently. This means that someone could be attracted to one person, be attached to another person and have a sexual relationship with someone to whom they are neither attracted nor attached.
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1Fisher, H. E. et al. (2006). Romantic love: a mammalian brain system for mate choice. Philosophical Transactions of the Royal Society, 361, 2173-2186. doi:10.1098/rstb.2006.1938
2Gladikas, B. M. (1995). Reflections of Eden: My years with the Orangutans of Borneo. New York, NY: Little Brown and Company.
3Darwin, C. (1871). The descent of man and selection in relation to sex. New York, NY: The Modern Library/Random House.
4Beach, F. A. (1976). Sexual attractivity, proceptivity, and receptivity in female mammals. Hormones and Behavior, 7(1), 105–138.
Sara Seabrooke
Dr. Seabrooke obtained her Ph.D. in Genetics in 2010 from the University of Toronto and completed post-doctoral training at McMaster University in 2012. While at McMaster Dr. Seabrooke was a course instructor for Genetics and ran a research project studying neuroprotective genes in the blood brain barrier. In addition to being chair of the SAB and CSO of Instant Chemistry, Dr. Seabrooke is a lead scientist at Inceptum Research and Therapeutics.
image source: amusingplanet.com 
