"Why are Brexit's political champions so unimpressive?" asks Janan Ganesh. Making the same point, Simon says:

The political system fails to select for competence, understanding or respect for wisdom and knowledge.

But why do we have such underwhelming politicians?

Here, we must guard against two errors. One is the tendency to believe that people are stupid just because they disagree with us. The other is a tendency to romanticize the past: it's not that politicians were all giants years ago, but that we have grown up.

Nevertheless, I suspect Janan and Simon have a point. Looking just at Tories (so as to avoid the former error) I am less impressed now than I was in the 80s. No top Tory has the clarity of mind and purpose that Thatcher had: Thatcher inspired hatred on the left whereas May arouses only contempt - that's a big difference. Boris Johnson's predecessors at the Foreign Office such as Carrington, Howe and Hurd had an integrity and seriousness of purpose which he wholly lacks. And - I'm showing my age here - even Nigella's dad once had an intellectual credibility which is absent from most senior Tories now.

This poses the question: what are the mechanisms which have selected for such mediocrities?

Politics has always been a profession where once can succeed through luck as well as merit (maybe even more than merit), and so attracts overconfident second-raters. But there might be other things at work. Here are a few theories.

- Declining Tory party membership. The Tories were once a mass party; they had over two million members in the 50s. Today, they are a handful of "weirdos and oddballs" who are "apart from reality", to use Richard Bridger's words. This means that whereas Tory MPs were once selected for their ability to appeal to sane and reasonable folk, today one can become a Tory candidate by enthusing weirdos.

- The rise of narcissism. The only thing we expect of politicians today is that they echo our prejudices, not that they exercise good independent judgment or promote the public good; the fact that there is a demand for referendums demonstrates a distrust of our elected representatives to do their job. We thus prefer the third-rate fanatic to the serious sober-minded man. The media, of course, is complicit in this. The right-wing press bullies independent-mined MPs, whilst the BBC - in its pursuit of balance - describes outright lies as "controversial claims".

- The Tories' loss of contact with business. In backing Brexit and immigration controls, Tory policies are not business interests. Of course, relations between the Tories and business haven't always been close: in 1980 CBI boss Terry Beckett threatened a "bare-knuckle fight" over monetarism. But the Tories then had links to corporate life which gave them roots in a reality-based community. Today, those roots are weaker.

- Increased inequality. Financial rewards in finance or business are now higher, relative to those in politics, than they were in the 70s and 80s. People of even moderate ability are, therefore, more likely to stay away from politics. Why become a cabinet minister to be harangued by a bigot earning five times as much as you, when you can earn more, with more dignity, elsewhere?

- The loss of public intellectuals. Thatcher could (and did) draw upon serious thinkers such as Popper, Hayek and Friedman. There are no equivalents of these today. The best Brexiters can manage are a bunch of cranks whose work doesn't withstand scrutiny.

Of course, none of this is to say that intelligent public-spirited people are always weeded out: they are not. It's just that there are mechanisms which tend to select against such people. Nor is it the case that politics is unique in tending to select against honesty and merit. There are adverse selection mechanisms in many organizations. The point is, though, that we should not just decry the mediocrity of our political leaders, but ask what mechanisms give us such inadequates? And how, if at all, can these be changed?