When you consider the resistance that other genetic variations provide such as Tay-Sachs (resistance to tuberculosis) and sickle cell anemia (resistance to malaria), it makes sense that another variation could have become more common under the pressure of a plague.
There was a documentary concerning this on the History Channel last year.
My comment was not with regards to whether resistance can develop in a population. Of course it can.
It was with regards to whether it would develop to a greater extent in Europe than in the Middle East, India and the Far East, areas where the population was exposed to repeated epidemics of plague for a much longer period than in Europe.
Interesting. Didn't know that.
Did some googling and found that Cystic fibrosis heterozygotes are resistant to cholera toxin.