"One reason is that female managers tend to work in so-called functional specialties (such as HR) rather than line management, which is the main hunting ground for the very top but often involves extensive travel and unsocial hours. More importantly, boards have traditionally been made up of white middle-aged males of similar backgrounds who are comfortable with each other and recruit new colleagues in their own image.
"Women, even if they can be found, "are a bigger risk," says Joanna Barsh, a director in McKinsey's New York office; they have a different style and are more visible, so if something goes wrong everyone notices. Some women find the culture of organizations so off-putting that they see little point in rising to the top." Read more in the Economist.