This makes for depressing reading.  We know that the majority of CEO's are male - only 6% are female - but this article talks about why.  

The general view that it's a question of lack of pipeline - that there aren't enough talented women in the upper echelons ready and waiting to step up into the corner office - but that the numbers are swelling and that change will come in time -  would seem to be flawed.  Well worth a read.