A hundred years ago, there was comparatively little social mobility. Among the working classes there were many people with high levels of ability - intelligence, initiative and confidence; meanwhile, the upper classes were stuffed with idle dimwits. The First World War was characterized by thousands of pointless deaths, ordered by chinless wonders.
Over the past sixty years, many able and hard-working individuals from unprivileged families have attained social status and economic prosperity. Meanwhile, some formerly wealthy families have slipped down the socio-economic ladder, as a result of folly or misfortune.
As a result of this increased opportunity for social mobility, the distribution of power and wealth, although far from perfect, is perhaps very slightly better aligned to merit than it had been. And although there are many injustices and anomalies, with too many arrogant idiots in powerful positions, and there is still discrimination against talent in some areas, society has undoubtedly benefited from taking its leaders from a much broader pool of talent, women as well as men.
The question now arises - is there an unlimited supply of talented people in the under-privileged sectors of society? Should we expect levels of social mobility to remain constant? Should we expect mediaeval institutions like the British Army, Oxford and Cambridge Universities, the House of Commons, the BBC and Northern Rock to take a fixed proportion of their intake from under-privileged sources?
Meanwhile, the people who climbed the ladder fifty years ago might wish to pull the ladder up behind them, making sure that their own bright and beautiful children and grandchildren get to the front of the queue for the best universities and the best jobs. However, since some of these parents got where they are today by ability and hard work, as well as good fortune, it is just possible that a few of these children might be pretty talented anyway.
I have no doubt that there are still many able and hardworking people from underprivileged backgrounds, who could play an extremely valuable leadership role in society, and I have no wish to discourage them or deny them the opportunity to fulfil their potential. But given the large number of able and hardworking people who have already moved from the working classes into the middle classes, it is possible that the amount of potential talent remaining in the working classes may be slightly less than it was a generation or two ago.
It is also conceivable that ability and hard work are socially determined. Indeed, one of the reasons why well-off parents send their children to expensive schools is because they believe that this will provide an environment in which hard work is rewarded, thereby bringing out their children's latent ability.
Actual social mobility may be clustered - it may make sense for waves of talented people to move upwards together, as they did in large numbers into many professions after the Second World War. Clustering may not be fair to everyone, but it may produce satisfactory outcomes for large numbers of people.
So this is a complex and highly charged political topic, which touches some raw nerves on both sides of the political spectrum. Enter one brave academic: Bruce Charlton, who is Reader in Evolutionary Psychiatry at the University of Newcastle upon Tyne, has recently suggested that the low numbers of working-class students at elite universities was the "natural outcome" of IQ differences between classes.
I have not seen the evidence from which Dr Charlton draws this conclusion, and I have been careful not to make any such sweeping assertions myself. All I wish to say here is that social mobility is a more complex phenomenon than most politicians are willing to admit, and that educational policy based on a over-simplistic and linear notion of social mobility and distributive justice may be fundamentally flawed.
Update: New evidence is being published to show how the professions are increasingly "reserved for the rich". [BBC News, 21 July 2009]