The answer to the question whether the quality of the crops would revert to equal is yes. There is a "natural experiment" in the UK population which demonstrates this. Prior to the Second World War the disparities in quality of diet and of other living conditions between the working class population and the rest of society were very great. There was a striking disparity between average height of working class people and the rest of the population, but wtih considerable variation within the groups - there were some short people in the well-fed population and some tall people amongst the poor, but a marked difference between the mean heights of the two groups. In the post-war Welfare State the living conditions of the well-off population remained good but there were very large improvements in diet and living conditions for working class people. The consequence was that the disparity in height largely disappeared. In the pre-war population there were very few people over 6ft tall in the working class population - in a modern state school the size distribution is virtually identical to that in fee-paying schools. The genetics of the working class population had not changed in any way - the change occurred because they could only reach their full potential height if well nourished throughout childhood.

It is probable that genetics makes a contribution to the variabiity of intelligence within a population. There is compelling evidence that one cannot compare two populations unless they have access to equally good living conditions and schooling.

The political message is very simple - if you are a member of a privileged group and you wish to preserve that privileged status you must vigorously oppose any measures to improve living conditions and/or educational opportunities for the underprivileged or they will catch you up.