Author and journalist Christine Wicker noticed a surprising trend: 66% of divorces are requested by wives. To try and understand why this was the case, Wicker researched the history, statistics and consulted with experts. Here are some of her key findings:

University of Virginia research shows that progressive wives are less happy than traditional wives. Rutgers University biological anthropologist Helen Fisher sees the rise of working women as a cause of women asking more from marriage.

Since the 1950's gender roles have changed significantly. Though men do tend to do more housework and child care now, a common gripe amongst women who leave their husbands is that husbands feel like simply one more child to take care of.

" I have examined divorce patterns in 58 societies and everywhere that spouses have some independent means, both sexes leave bad marriages to make better ones." -Helen Fisher

Theories abound as to why women tend leave marriages. One reason could be that contrary to popular belief, long marriages don't get happier over time. In 2001 an analysis of marital happiness studies showed a steep decline toward the later years.

Another theory is that the earliest humans didn't hold themselves to the expectations of a lifelong marriage as most do today. Data suggests that many ancestral men and women had two or three spouses across their lives.

Midlife restlessness due to menopause could also be a factor. The hormone oxytocin is a major component in bonding. During menopause this hormone reduces in women and testosterone increases which can increase independence.

Another component is that in midlife, women can become unhappy with their life accomplishments, especially if their husbands are experiencing life and career success. This can be a factor in wanting more out of life and pursuing a new path.

Sociologist W. Bradford Wilcox, director of the National Marriage Project, has research showing that emotional commitment - how affectionate and understanding husbands were - was the most important factor in wives' happiness. Fairness was also important, but not vital.

Finally, women tend to bear the burden of the "emotional load" of the relationship. Monitoring closeness, connection and commitment. This takes a toll especially when the husband is not receptive to the issues women point out. Without this, women are likely to walk away.