Have you lost that "lovin' feelin'"? The Righteous Brothers may not know it when they sang the number-one hit single in 1965, but you can blame a hormone called neutrophin:
A team from the University of Pisa in Italy found the bodily chemistry which makes people sexually attractive to new partners lasts, at most, two years. [...]
The Italian researchers tested the levels of the hormones called neutrophins in the blood of volunteers who were rated on a passionate love scale.
Levels of these chemical messengers were much higher in those who were in the early stages of romance. [...]
But in people who had been with their partners for between one and two years these so-called "love molecules" had gone, even though the relationship had survived.
The scientists found that the lust molecule was replaced by the so-called "cuddle hormone" - oxytocin - in couples who had been together for several years.