It is the butt of jokes at dinner tables, the source of arguments at family gatherings and has even been grounds for divorce.

Now, the reason behind the age-old problem of feuding between mothers-in-law and their sons' wives has been answered. Wives are programmed to dislike their partner's mom.

A new book by a British relationship expert, Dr. Terri Apter suggests that even if a wife or girlfriend wanted to like her in-law, she already has an expectation they won't get along, The Daily Telegraph reports.

More than 200 people, including 49 couples, were interviewed for the book.

Almost two-thirds of women complained they had suffered long-term stress because of the friction with their husband's mother.

Apter, a psychologist and senior tutor at Newnham College in Cambridge, U.K., said both wife and mother-in-law assumed that each was undermining the other.

"This mutual unease may have less to do with actual attitudes and far more to do with persistent female stereotypes that few of us manage to shake off completely," she said. "Both mother and wife are struggling to achieve the same position in the family — primary woman."

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