All-male boards, I reported recently, are bad for business. A new study confirmed what previous research already told us -- female-free boards make for worse decision making and cost a company money. Lots of money, actually. Which is a pretty compelling reason for firms to fix the issue if their boardrooms are less diverse than they should be.

But if this rationale isn't enough for you, another study recently added yet one more argument to the case for including women on boards.

If diversity leads to cleverer and more lucrative business decisions then, obviously, smart companies should aim to be as diverse as possible. It's a simply logic, but one women apparently tend to understand more than men do.

Going to bat for all kinds of diversity

That's one conclusion of a new survey from consultancy PricewaterhouseCoopers. The poll of 800 public company directors asked respondents to weigh in on how much they valued diversity. You'd expect women, who benefit from gender diversity, to be all for it, and indeed they are. Among female respondents, 63 percent said gender diversity was "very important." Just 35 percent of male directors agreed.

The surprise came when PwC asked about racial diversity. There's no self-interest in women being more interested in getting folks from different racial backgrounds onto boards, but here too they showed a markedly higher level of enthusiasm than their male peers. Nearly half (46 percent) of women said racial diversity was very important. And the men? Just 27 percent agreed.

Women are also more optimistic that there are qualified candidates from a variety of backgrounds out there. About half (46 percent) told PwC that good, diverse candidates exist, while only 18 percent of men concurred.

If you buy the rationale that diversity is a business essential (rather than mostly a PR exercise or simply an ethical imperative) than this is one more reason to hope we see more women in boardrooms soon. Not only do they represent greater diversity themselves, they're more likely to fight for directors who are more representative in other ways as well.