Before revision: Recent works in quantitative evolution have shown that biological structures are constrained by selected phenotypes in unexpected ways . This is also observed in simulations of gene network evolution, where complex realistic traits naturally appear even if they have not been explicitly selected . An important biological example is the absolute discrimination between different ligand "qualities", such as immune decisions based on binding times to T cell receptors (TCRs) or Fc . In evolutionary simulations, the phenomenon of absolute discrimination is not achieved without detrimental ligand antagonism : a "dog in the manger" effect in which ligands unable to trigger response prevent agonists to do so.
After revision:  . In evolutionary simulations, the phenomenon of absolute discrimination is not achieved without detrimental ligand antagonism : a "dog in the manger" effect in which ligands unable to trigger response prevent agonists to do so.