One of the great things about the Davies Review of board diversity is that its rather modest proposals (a voluntary target of 25% female representation on FTSE100 boards by 2015) is that it had caused an outpouring of articles criticising the proposals. I think this is useful because a) it helps to read opposing views to sharpen your thinking and even sometimes make you change your mind and b) some of it is simply funny. That said the minute I wasted skimming Cristina Odone's entirely predictable piece on the subject is one that I will never get back.
Anyhow, one of the less compelling arguments against I've seen advanced so far is the one that if there were really anything the link between female board representation and financial performance then companies would already have diverse boards. In short if there is money in diverse boards obviously companies would have them, and shareholders would want to ensure that this happens. All is for the best in the best of all possible worlds.
I think this is mistaken for several simple reasons.
First there is the simple availability of evidence point - companies may not be aware of research suggesting such a link, since it's not an intuitive one.
Second, there could be a problem of interpretation of evidence - for a variety of reasons companies may not accept the validity of such research. Cognitive biases
Third, some boards may think that whilst there could be a link it's not relevant to them (could be an engineering firm where women are a small minority of the workforce so internal appointment v unlikely).
Fourth, companies may consider that even if there is a link between board diversity and performance it is likely so small that actively seeking to improve diversity is not worth it.
Fifth, it could be an entirely rational outcome for both women and boards, based on existing expectations, for the former to not put themselves forward and for the latter to not seek the former out. On these last two points I think Thomas Schelling's modelling on mild preferences could tell you a lot then about how even mild preferences for male directors could have large aggregate effects.
Note none of the above require you to have any cartoony view of sexist boards and directors to lead you to consider that actually they wouldn't necessarily take the optimal approach to diversity. I suppose the question back would be well, yeah, in theory that might be true but in practice companies are efficient and wouldn't allow an obvious defect to go without being addressed. Two v brief points in return -
1. M&A activity. Lots of different studies suggest that a lot of companies undertake many deals that do not create, and often actively destroy, value. This information is widely available, yet companies seem to think that they uniquely will buck the trend. In other words boards repeatedly undertake inefficient activities. Is it really too much to believe they may also get it wrong on gender?
2. Corporate leaders tend to be taller than average. Is this because there is a correlation between height and ability to run a company, or is it because we have a subconscious image/stereotype of what a leader looks like that can affect our decision-making? And if we can get confused about height, it seems reasonable to assume we might occasionally trip up with gender.