chain), with a length
of approximately 100 amino acids. What shapes the evolution of the
immune receptor libraries is largely unknown. Given that epidemics
have been an important selection pressure in the evolution of human
populations we expect that the these gene libraries bear the traces of
the antigenic exposures of the species. On the other hand, immune
responses to artificially-produced molecules have been induced in
mice, suggesting that the immune system is able to recognize more than
the antigens that the species encountered in its evolution. These
observations lead to the idea that the immune system creates its
receptors so as to be able to recognize as many molecular shapes as
possible. Was the immune system evolved in such a way, or does it only
focus on the molecular shapes that are most detrimental to the
survival chance of the organism?
In the following section I will explore the scaling between the fitness of the organism-defined as its probability to survive in a pathogenic environment-and the size of its antibody repertoire. I will argue that the functional form of this dependency suggests that the role of germline diversity must be to broadly map the regions of the pathogen space that are relevant for the survival of the organism. Moreover, I will argue that biases in the pathogen exposure of the individuals, such as sampling the pathogen universe, would preclude the evolution of germline-encoded antibodies that optimally cover the complete space of molecular shapes. Thus, contrary to what is commonly believed, I argue that the immune system does not handle as many molecular shapes as possible. It rather focusses on those that have been important for the survival of the species. Responses to artificially constructed molecules are possible because these molecules are sufficiently similar to epitopes that are encountered on pathogens.