Love can be a blind biological mechanism for initiating a new generation of human genes and protecting their carriers in their vulnerable early years. This sort of love falls into two phases of unequal length: a short phase of sexual infatuation and a long phase of habit and inertia.
The infatuation phase sees much exchanging of saliva, sperm and body gases, each with their individual character and freight of microbes and viruses, and this might do more than merely prepare the female partner's immunity system to tolerate a possible foetus with its foreign DNA. It might also induce a subtle form of addiction in both partners, which keeps them together during the habit stage that follows close behind.
There are indeed such a thing as love, and it indeed involves tenderness, concern, affection and regard, though not perhaps the desire and possessiveness which are the attributes of infatuation.
On the other hand, some people achieve love in the mythical sense of the romances, by turning their infatuation phase into a permanent state. The secret? Always making time for imaginative good sex.
A.C. Grayling - The Heart of Things.