Immunoglobulins did not arise in evolution to fight infection.

The complex interactions between B and T cells in response to external antigens are the major focus of contemporary immunology. Here, John Stewart argues that they may be relatively late evolutionary developments, due to the redeployment of a system invented for other reasons. He suggests that the system of variable region molecules (VRM) arose, at the time of the first vertebrates, by an endogenous, self-organizing process; this primordial VRM system instituted a molecular ecology, a function so important that from then on no vertebrate has been able to do without it.