Helen Fisher: The Laws of Chemistry

"We form enduring pair bonds. The vast majority of other mammals—some 97 percent—do not.
Humanity has evolved three distinct but overlapping brain systems that enable us to fall in love and form long-term emotional connections: the neural systems for the sex drive, romantic love, and attachment. We are all alike in having these three primary brain networks. In other ways, however, each of us is unique. We don't fall in love with just anyone. We have deep and idiosyncratic preferences."


Psychology Today: The Laws of Chemistry