Research indicates that long before written history, primitive clans and tribes were living within small, highly inter-dependent social structures.
Many of these groups had some type of ceremony marking the forming of a union or marriage between two opposite sex partners.
It appears that since we began living in structured social groups, humans have adhered to the belief that formal unions of two people work best for maintaining a healthy, functioning society.
Within different societies, independent unions of two people, were considered the best way to secure food and shelter, defend against outside aggressors, and raise offspring. As societies evolved, the marriage bond took on increased significance within each culture.
One of the most universal aspects of the marriage union to be perpetuated cross-culturally was monogamy.
Yet despite this proclivity towards marriage, and insistence that the marriage partners remain monogamous, human beings have been engaging in non-monogamous activities throughout history.
so, i think its not something new but i must say that it has increased in present times due to advancement in communications.
[B]but my question is that why are so many people having affairs despite such powerful social and religious doctrines against them? [/B]

my dear members of forum have presented so many reasons which are absolutely true thats why i dotn want to repeat them.....
but believe me some people innitiate these relations only for desire to get a partner jealous... and then indulge in it so deeply then they cant find any way out.
in most of the cases it breeds as a result of unsatisfactory relationship, high level of expectations shatterd trust etc etc.
we must point out the source or loop holes in relationship and then work on our weak points..... in order to save relations from the trap of this extramarital affairs tag.

i think self-assesment is very important .