Humans have evolved to have monogamous relationships, especially women are predisposed by their genetics to have affairs as "back-up plans'" if their relationships fail, according to a research paper.
Scientists at the University of Texas have put forward the "mate-switching-hypothesis" which says humans have evolved to keep testing their relationships and looking for better long-term options.
The senior author of the research, Dr David Buss, said, "Lifelong monogamy does not characterise the primary mating patterns of humans. Breaking up with one partner and mating with another may more accurately characterise the common, perhaps the primary, mating strategy of humans."
Dr Buss said: "Affairs serve as a form of mate insurance, keeping a back-up mate should a switch become warranted in the future."
Another study carried out by Rafael Wlodarski and a team of researchers at Oxford University looking into infidelity found a correlation between the length of a individual's ring finger and the likelihood that they would cheat on a partner. However, they stressed that they could not find a causal link.