Love rats - Mick Jagger, Alan Clark et al - and infidelity have become the salt in our daily diet.
We watch it in our soaps; demand at least a confession a day from the telly or the newspapers; anticipate it regularly from our royals and lap it up in colour across pages of Hello!. Adultery is Britain's best-loved national sport. So what will we make of the news that scientists have now discovered a genetic basis for monogamy?
Tom Insel and Larry Young, neuroscientists working in Atlanta, Georgia, have transferred a gene from monogamous male prairie voles into aggressive, promiscuous mice and produced the perfect mate - faithful, attentive, too damn good to be true. Modestly, the scientists point out that in human beings, behaviour may be governed as much by contemporary values and conditioning as it is by biology.
Still, many a woman may decide that if the choice lies between dancing alone round her handbag drunkenly singing, "I Shall Survive" for yet another Saturday, or her resident Lothario swallowing a couple of genes a day, her money is on the genes.
At last, you might say, the scientists have come up with the happy ending to the crisis in matrimony we are told so much about: no more affairs; commitment rules OK. Or does it? This vision of what guarantees wedded bliss fails to acknowledge the contradictory make-up of human beings (not least in that those addicted to love rats follow the principle that if somebody else wants him, he must be worth having), and the complexity of our modern relationships. Or, to put it another way, monogamy is the least of our problems.
According to research (and who knows how truthful individuals are when questioned about their bit on the side?), 80-90 per cent of us disprove of adultery, at the same time that a proportion indulge in it. Infidelity is largely a posh person's activity. One in eight men in social classes one and two has had a recent extramarital affair, but only one in 40 in social classes four and five. The reason isn't honour but opportunity - or rather, the lack of it. Upper-class men travel more, goes the theory, so they have greater chances of having a liaison.
Women, too, of course, are unfaithful. Again, they are twice as likely to be unfaithful as women in general if they work away from home. Men are more likely to petition for divorce on the grounds of their wives' adultery - 37 per cent of men, compared to only 22 per cent of women. But adultery is cited as cause for divorce in only 24 per cent of marriage breakdowns. And here we come to the crunch.
Married or cohabiting, fidelity matters, but what is proving even trickier for long-term relationships is the business of negotiating daily life - who does what, who says what, in the myriad battlefields of work, money, children and sex. This is further complicated because in the early stages, according to Professor Alfons Vansteenwegen, "Love is a disease of the eyes", so we see the object of our affections as we would wish him or her to be, not as they are. Words are avoided. Then, as writers such as Deborah Tannen and John Gray have made fortunes from pointing out, once we men and women do open our mouths, we discover that we speak a different language despite using similar words.
In spite of it all, what many of us are still seeking, according to academics such as Dr Christopher Clulow, is the "companionate relationship", inside or outside marriage. One in which, ideally, issues are settled by negotiation and compromise on the basis of equality - a feat that requires each partner to be aware and have sympathy for the world in which the other lives. (In short, the breadwinner doesn't tell the house-husband, when home from work, "God knows what you've been doing all day...".)
Given that handling a relationship is fast resembling another form of rocket science, we begin to see why some errant partners nip off for the (initial) simplicity of a quick leg-over. In practice, the three main reasons for infidelity are a fear of commitment, the lure of forbidden fruit and a break for freedom. (I would have thought an insatiable appetite for having one's ego boosted might come fourth.) All of which, of course, will no longer be appropriate once the monogamy gene is administered as to babies at birth.
So, no more Casanovas - boring or what?