What is Love? An Evolutionary Perspective
Love is at least as old as the written word, and as unsullied by the vicissitudes of time as the ancient clay tablets that first chronicled its poetic creations. Four thousand years ago, a young priestess wrote of her love for the king of Sumer; the first civilization to develop writing. The cuneiform clay tablet inscribed with the poem was unearthed a century ago in Iraq. It revealed a story of captivation and seduction that would be at home in any modern day erotic novel . It seems that love is an unalterable and universal facet of the human condition; so how did it get there?
Why Do We Love?
The best way to illustrate the necessity of love is to imagine two couples living millions of years ago. The first couple is a loveless union. When the woman falls pregnant, the father abandons her to search for other mates. The second couple is in love, and when the woman becomes pregnant, the father remains by her side. For the first couple, the mother will be at risk of attack from rivals or beasts during pregnancy, and the child’s upbringing will be dangerous without the protective presence of the father. In looking for other mates, the father will be risking injury and death by competing with other males for female affection. For the second couple, the mother will be protected during pregnancy and the child will be protected during its upbringing. Once the child is born, the father will be able to have another child with the mother, giving him long-term access to a fertile mate.
In these scenarios the loving couple is more likely to live longer, and their children are more likely to survive to adulthood. This means their genetic material is more likely to be passed on to the next generation. Within this material will be the genetic anomalies that caused them to love each other. Over time, the descendents of the loving couple will become far more numerous than the descendents of the loveless couple. Eventually all humans will possess the genetic anomaly that causes us to love. In other words, love is a naturally selected genetic trait that helps humans to survive .
- Fessler and Haley (pdf)
This academic paper includes a section on the evolutionary benefits of romantic love, as well other adaptive strategies of affect that enhance cooperation in social contexts.
What Is Love?
Love is whatever is needed to hold interpersonal relationships together in a way that helps an individual pass on their genetic material. This commitment is marked by increased affection, compassion, and intimacy in romantic, familial or friendly interaction.
Love is often claimed to be of divine origin because of its intangible nature and the purity of its pleasurable effect. However, the extreme passion that characterises love will reduce any human ability to rationally reflect on the experience. This explains why a priori descriptions of love are typically poetic or metaphorical. The competition between males for the affection of females would have served to exaggerate love (my love is greater than yours) and skew its definition (my love is unique and special), prompting further allusions to its indescribable purity. Indeed, love may be difficult to define for precisely this reason. If one cannot describe their love for another in a formulaic way, then it appears special, increasing the chance of reciprocation. Love may have evolved to be confusing.
Love, The Emotion
Love is best explored as an emotion with physiological indicators. The British professor and television presenter, Robert Winston, has shown that the emotional state of love involves the release of chemicals that stimulate the pleasure centres of the brain . The release of these chemicals, such as dopamine and serotonin, demonstrate love to be a positive emotion that reinforces attachment behaviour. In contrast, lust is a negative emotion because it drives people to prevent a negative outcome (not having sex!) by changing their behaviour towards finding a partner. This is why romantic love typically follows lust, and why they are different emotional states.
In summary, if love wasn’t indescribable we wouldn't see it as personal and unique, and its evolved function for holding together families would be degraded. Love is blind because sometimes it’s better not to see.
 Diane Wolkstein (1983) Inanna, Queen of Heaven and Earth: Her Stories and Hymns from Sumer, Harper Perennial.
 Helen Fisher (2006) Why We Love: The Nature and Chemistry of Romantic Love, Henry Holt and Co.
 Robert Winston (2005) Human, Dorling Kindersley Publishers Ltd.