July 23, 2005 -- News of famous actor Jude Law's recent infidelity has been splashed across newspapers and magazines everywhere, sparking interest once again in the age-old debate of why people cheat.
Law joins other high-profile people who have been caught in the act. But, it's not just celebrities who cheat; ordinary people also cheat, even though they are not rich or powerful.
A recent ABC News poll found more than two in 10 men admitted they had an affair. And it's no secret women stray too.
According to Hal Sparks, host of E!'s "Talk Soup," cheating happens with both men and women because human beings are not chemically engineered to be monogamous.
"Nature hates two things, virginity and monogamy," said Sparks. "We are not built that way. You can civilize yourself, you can absolutely bonsai tree your soul, but your nature will be to go forth, be fruitful and multiply at every possible opportunity."
This is not entirely true, according to anthropologist Helen Fisher. In an interview with ABC News' "Good Morning America," Fisher said human beings are among 3 percent of the world's 4,000 species of mammals pre-programmed for monogamy.
"First of all, 75 percent of men do not cheat, and 85 percent of women do not cheat," said Fisher. "The brain is built for pair bonding."
Scientists are now focusing on a "monogamy gene" in vole mice, or field mice, which is said to promote monogamous behavior.
According to Fisher, when the non-monogamous meadow vole was injected with the monogamy gene from its close cousin the prairie vole, there was a noticeable change in its behavior. Instead of mating and immediately moving on, the meadow vole would show more of an attachment to its mate.
Could this be the miracle cure for wayward folks?
Unfortunately not, said Fisher. The monogamy gene is broken down into three parts -- lust, romance and attachment -- and in some cases these three don't work together.
"You can feel a strong attachment to one person and mad romantic love for someone else," said Fisher.
Fisher also said environment is a big factor in determining whether someone will cheat. If someone is lonely, or in an unhappy relationship, the monogamy gene may be overriden by these feelings.
And contrary to what many might believe, Americans are not among the world's leading cheaters.
"We're relatively low on the cheating pole," said Fisher. "Americans work too hard, we don't have enough time, we have a lot of property, and we have a long history of regarding adultery as sinful."