2. Scientific views

Main article: Love (scientific views)
Throughout history, philosophy and religion have done the most speculation on the phenomenon of love. In the last century, the science of psychology has written a great deal on the subject. In recent years, the sciences of evolutionary psychology, evolutionary biology, anthropology, neuroscience, and biology have added to the understanding of the nature and function of love.

• 2.1 Biology of love

Further information: Interpersonal chemistry
Biological models of sex tend to view love as a mammalian drive, much like hunger or thirst. Helen Fisher, a leading expert in the topic of love, divides the experience of love into three partly-overlapping stages: lust, attraction, and attachment.

Lust is the initial passionate sexual desire that promotes mating, and involves the increased release of chemicals such as testosterone and estrogen. These effects rarely last more than a few weeks or months. Attraction is the more individualized and romantic desire for a specific candidate for mating, which develops out of lust as commitment to an individual mate forms. Recent studies in neuroscience have indicated that as people fall in love, the brain consistently releases a certain set of chemicals, including dopamine, norepinephrine, and serotonin, which act similar to amphetamines, stimulating the brain's pleasure center and leading to side-effects such as an increased heart rate, loss of appetite and sleep, and an intense feeling of excitement. Research has indicated that this stage generally lasts from one and a half to three years.

Since the lust and attraction stages are both considered temporary, a third stage is needed to account for long-term relationships. Attachment is the bonding which promotes relationships that last for many years, and even decades. Attachment is generally based on commitments such as marriage and children, or on mutual friendship based on things like shared interests. It has been linked to higher levels of the chemicals oxytocin and vasopressin than short-term relationships have.

In 2005, Italian scientists at Pavia University found that a protein molecule known as the nerve growth factor (NGF) has high levels when people first fall in love, but these levels return to as they were after one year. Specifically, four neurotrophin levels, i.e. NGF, BDNF, NT-3, and NT-4, of 58 subjects who had recently fallen in love were compared with levels in a control group who were either single or already engaged in a long-term relationship. The results showed that NGF levels were significantly higher in the subjects in love than as compared to the either of the control groups.

• 2.2 Psychology of love

Further information: Human bonding
Psychology depicts love as a cognitive and social phenomenon. Psychologist Robert Sternberg formulated a triangular theory of love and argued that love has three different components: Intimacy, Commitment, and Passion. Intimacy is a form by which two people can share secrets and various details of their personal lives. Intimacy is usually shown in friendships and romantic love affairs. Commitment, on the other hand, is the expectation that the relationship is going to last forever. The last and most common form of love is sexual attraction and passion. Passionate love is shown in infatuation as well as romantic love. This led researchers such as Yela citation needed to further refine the model by separating Passion into two independents components: Erotic Passion and Romantic Passion.

Following developments in electrical theories, such as Coulomb's law, which showed that positive and negative charges attract, analogs in human life were developed, such as "opposites attract". Over the last century, research on the nature of human mating, such as in evolutionary psychology, agree that pairs unite or attract to each other owing to a combination of opposites attract, e.g. people with dissimilar immune systems tend to attract, and likes attract, such as similarities of personality, character, views, etc. In recent years, various human bonding theories have been developed described in terms of attachments, ties, bonds, and or affinities.

Some Western authorities disaggregate into two main components, the altruistic and the narcissistic. This view is represented in the works of Scott Peck, whose works in the field of applied psychology explored the definitions of love and evil. Peck maintains that love is a combination of the"'concern for the spiritual growth of another", and simple narcissism. In combination, love is an activity, not simply a feeling.