It's a tale we have all heard before. They've been together for 20 years or so. The children are grown up and they've grown apart. She gets a new career and he gets a new wife.
All too often it's the man who gets the blame in this scenario with many attributing it to the mid-life crisis. But in fact it may be more to do with the female species and more precisely a natural change in her brain, which alters the way she thinks, perceives and even acts.
According to American psychiatrist Louann Brizendine, it comes down to Mother Nature unplugging the "mummy part" of the female brain, which she does by reducing the supply of hormones which promote maternal, caring, peace-promoting instincts.
In her book The Female Brain, Brizendine says this change comes about with menopause - the last big hormonal change - after which the brain is no longer subjected to the surges and fluctuating hormones, which came with the menstrual cycle and resulting in moodiness, depression and even the ability to see insults when they were not intended.
<b1>Brizendine, a neurologist and the founder of the University of California's Women's Mood and Hormone Clinic in San Francisco, says throughout the child-bearing years, the female brain is marinated in oestrogen - a hormone which effects the amygdala and prefrontal cortex, the emotional processor and emotional assessment and judgement area of her brain.
The effect of this heightens a woman's communication and emotional circuits, giving rise to those maternal instincts, which tend, care and do the best they can to avoid conflict to give the family unit the best possible chance of survival.
Menopause brings a dramatic change. Levels of this hormone fall, as does the level of oxytocin, the "bonding" hormone, and the sex drive hormone testosterone.
These changes bring physical symptoms along with potential health problems such as increased risk of osteoporosis, certain cancers and cardiovascular disease.
But, says Brizendine, it also puts an end to the fluctuating hormone levels and with it comes a much more stable brain and a less maternal woman. A woman who, she says, is "less worried about pleasing others and now wants to please herself" and that may mean taking on new challenges or a new job and leaving the old life, including her husband, behind.
The theory is certainly borne out by statistics worldwide, which claim the majority of divorces in couples over the age of 40 are initiated by women.
Hong Kong clinical psychologist Katherine Kot Lam-kat, who counsels women on problems encountered at menopause, agrees many women do experience a change in their state of mind at this time of life.
However, she says more research was needed before it becomes clear what role hormones played or whether it was simply down to women moving into a different stage of development caused by their change in circumstances.
"When children grow up, women go into a different stage of personal development," she says. "They realise their children are grown up and they have own lives. That has a big impact on them because they realise they have to switch roles."
"With this comes a change of identity from the mother and wife. They have to find a new role for themselves and they need to change direction. They realise that being a mother is not part of their life any more and ask 'what am I suppose to do with the rest of my life?'"
It all sounds like bad news for the husbands who witness the change and it can be a scary time, Kot admits.
"For men it is an unknown process," she says. "When a woman changes, the family dynamics change and relationships change. The uncertainty of all this can be scary for the men."
It has repercussions on society too. A study in Hong Kong found that this army of post-menopausal women make up one-sixth of the total population.
It's a modern, worldwide phenomenon as advances in medicine have given modern woman, unlike her ancestors, a life span up to 30 years beyond the childbearing years.
With around one-third of her life stretching ahead of her in this new altered and child-free state, it is not surprising that women want to question how they will spend those years, says Brizendine.
It can be hard, but it would help to encourage women to view their lives in two parts, Kot says, adding, "Part two begins when part one with children is over."
"It can be crisis. But any crisis can be a good opportunity. It's a time to look at what you really want and find your own value."
"You have to reflect on the different changes in life and find your own way. Maybe you choose to go back to school, work or to find your own position in society."