KEY POINTS:
Researchers have discovered that the trigger for the proverbial male midlife crisis may not be a man's age at all, but a reaction to his wife's imminent menopause.
Writing in the journal Psychology Today, doctors Alan S. Miller and Satoshi Kanazawa say a man's midlife crisis is often
jolted into being when his wife nears the end of her reproductive life and his evolutionary need to attract younger women is renewed.
Therefore a 50-year-old man married to a 25-year-old woman would not experience a midlife crisis, but if the situation was reversed, he would - in the same way that a 50-year-old man married to a 50-year-old woman would.
"It's not his midlife that matters; it's hers," Miller and Kanazawa write.
"When he buys a shiny-red sports car, he's not trying to regain his youth; he's trying to attract young women to replace his menopausal wife by trumpeting his flash and cash."
The midlife crisis findings are just one of ten "outrageous truths about men and women" published in the report.
Other assertions are that beautiful people have more daughters and that having sons reduces the likelihood of divorce.
Miller and Kanazawa say that according to a celebrated principle of evolutionary biology - The Trivers-Willard hypothesis - parents who have traits that will benefit one gender more than the other tend to have more children of that gender.
Although physical attractiveness is a universally positive trait, it contributes more to women's reproductive success than it does to men's, so it follows that attractive couples will have more female children.
Miller and Kanazawa say there is evidence to back this hypothesis, with Americans who are rated "very attractive" having a 56 per cent chance of conceiving a daughter as their first child, compared with a 48 per cent chance for everyone else.
But while attractiveness may be a positive trait for women, men are more likely to be judged on their wealth, status and power.
Sociologists and demographers say this mindset may be behind a more unusual finding - that couples with sons are less likely to divorce.
Miller and Kanazawa say the continued presence of a father in his son's life is important to ensure the transfer of wealth and status to the next generation.
However there is not much a father can do to perpetuate the things which are important for women; namely making his daughter more youthful or physically attractive.
"The presence of sons thus deters divorce and departure of the father from the family more than the presence of daughters," the report states.
Miller and Kanazawa's full findings will be published later this year in the book Why Beautiful People Have More Daughters.
