Why are women dropping out of corporate life so much younger than men? That was the question I found myself asking recently when I was looking at the CVs of prospective candidates for non-executive directorships.
I have conducted many similar searches as a member of the nominations committee during my time on boards in the UK, US and Europe. But on this occasion I was struck by two significant differences.
The first was that we were presented with a 50/50 selection of men and women. While this was a welcome new development, I suppose it was to be expected: most reputable headhunters have signed up to the Voluntary Code for Executive Search Firms, recommended in Lord Davies' 2011 report on gender diversity in the boardroom, which suggests that long lists of candidates should include at least 30% women. Kudos to Spencer Stuart for exceeding this.
What was more interesting was that the women were, on average, around seven to 10 years younger than the male candidates and so were, generally, somewhat less senior.
And while most of the men were seeking a single NED appointment to complement their full-time executive jobs, many of the women were planning to move out of full-time corporate life into a portfolio career, with a variety of roles in charitable, arts, public and private organisations. Some were planning to start their own company; others wanted to do community work.
None of them specified family commitments as a reason for stepping off the corporate ladder. They all dismissed this, saying that they had successfully balanced work and home life during their early careers when their children were young; those difficult years were now long past.
No, the overwhelming impression I got was that they had looked upwards and seen a sea of tired, grey-suited men above them and decided they just didn't want to join them.
These highly qualified, dynamic women, many of whom had 'potential CEO successor' written into their appraisals, didn't want their boss's job. The attractions of the C-suite, as the Americans call it, just didn't appeal.
Everyone accepts that gender diversity benefits senior executive teams. We are awash with facts and figures about how it brings about superior performance, higher share prices, bottom-line increases and all manner of good things.
We know that women are emerging in higher numbers and better qualified from universities and professional bodies.
We also know that most organisations have made significant efforts to recruit men and women in roughly equal numbers and have brought in more flexible job patterns to help women cope with work/life balance issues. Many young men with families are also taking advantage of these.
But all this clearly isn't enough. The problem is one of retention of women at senior level. We need to seal the leaky pipeline of executive women who will provide the role models for future generations - and who will help create the critical mass of women at the top that will bring about cultural change.
Perhaps the question to ask is not 'why do women drop out?' but 'why can't companies hang on to good women?'
McKinsey recently carried out a study of 200 women in senior executive roles and found that 59% of them did not aspire to the top positions in their company.
While this could be due to a self-imposed 'glass ceiling', they also found that: 'More than men, women prize the opportunity to pour their energies into making a difference and working closely with colleagues. Women don't want to trade that joy for what they fear will be energy-draining meetings and corporate politics at the next management echelon.'
My fellow MT columnist Luke Johnson has recently written that 'struggle is at the heart of enterprise: in a free market, competitors battle it out to seize share from others'. There is no doubt that the language of war, battle and competition feature prominently in corporate literature.
Indeed, the favourite bedside book of many CEOs is routinely said to be Sun Tzu's The Art of War. This certainly doesn't make very appealing reading to most women I know.
As long as the culture of corporate leadership is dominated by those motivated by power, combat and beating the other guys to reach the next step in the hierarchy, few women will aspire to join it.
Mixing my metaphors and using the round peg (women) in the square hole (corporate leadership) analogy, it is time for organisations that aspire to sustained diversity at senior levels - and the performance that goes with it - to knock off the sharp edges of their culture to make it more woman-shaped in order to retain the best talent.
Who knows? Many men might also prefer this to the Grand Theft Auto culture of many organisations.
Baroness Kingsmill is a non-executive director of various British, European and US boards. Lady Kingsmill can be contacted on email@example.com
Follow her on Twitter: @denisekingsmill