The story of how all this works can be found in a lengthy debate that was published on the web and which I have pilfered for your reading pleasure. You can find the links to the debate on the main page. The immune system is a defense against infectious diseases . Pathogens can evolve far faster than their hosts. An immune system that is allowed to undergo somatic evolution can evolve at a rate comparable to that of the pathogens.
Somatic evolution comes as two parts.
First , as the famous F1 test shows, there is somatic selection of the specificity elements that results in the elimination of any anti-S that is present. Each VLVH can be mutated in a way that chances specificity without inactivating the molecule. This means that the functional B cell repertoire has to be repeated as larger animals evolved. The smallest sample of B cells that retains the properties of the entire population is called a Protecton . If we were interested in other boundary conditions, the actual dimensions of a Protecton might change, but the relationships would not.