Listening to Lenny Henry on the Today programme this morning, I was reminded of a paradox about diversity.

What I mean is that there are (at least) three distinct meanings of the term. One is ethnic and gender diversity - ensuring that women and minorities are fairly represented in positions of power and prominence. A second is cognitive diversity - giving space to different intellectual perspectives. And a third is ecological diversity: having a variety of strategies and business models.

I would argue very strongly for diversity in the last two senses.A multiplicity of perspectives - or epistemological anarchism in Paul Feyerabend's words - can be a solution to the problems of (tightly) bounded knowledge and rationality; this is expressed mathematically in the diversity trumps ability theorem. And ecological diversity can protect economies from shocks: the 2008 crisis was so severe because there was a lack of such diversity in the financial sector because many banks were following similar strategies. In a changing environment, mixed strategies help ensure survival.

A big reason why I support gender and ethnic diversity is because I favour these other forms of diversity. There's evidence that ethnic diversity can promote innovation and productivity, probably because it contributes to diversity in these other senses.

Which brings me to my paradox. My support for all three types of diversity is, I fear, not widely shared. Quite the opposite. Whilst there is widespread support in words (if not deeds!) for ethnic diversity, some of the dominant trends of our time are working against diversity in the other senses. For example:

- The main political parties have become more homogenous in the sense both of squeezing out mavericks and in the sense of becoming increasingly dominated by career politicians to the exclusion of people from working class backgrounds.

- Managerialists' attempts to impose hierarchy and targets onto all organizations are an attack upon ecological diversity.

- Social media might have exacerbated the trend towards groupthink, in which dissonant views are shouted down.

- There's a variety of perfectly coherent views which are far less heard than their merits would warrant: Oakeshottian conservativism, small state Keynesianism, left Hayekianism and so on.

Such conflicting attitudes to the different concepts of diversity are evident on the Left. Lefties have been happy to call for more ethnic diversity whilst fiercely opposing free schools - though the latter, insofar as they have merit at all, are an example of ecological diversity.

Not that the vice is confined to the left. I suspect that those "socially responsible" bosses who want to promote women and minorities in their firm often do so by hiring those who think just like them - thus achieving ethnic diversity at the expense of cognitive diversity.

All this brings me to a variant of the question asked by Nkem Ifejika: what's the point of having so many ethnic minorities in positions of power and prominence if nothing else changes?

Mr Henry replied that doing so would level the playing field. That's reasonable insofar as it goes. But given that equal opportunity and social mobility are such weak ideals, I fear that it grossly undersells the potential benefits of diversity.