Immunological memory may not represent a special characteristic of lymphocytes but simply reflect lowlevel responses driven by antigen that is re–encountered or persists within the host. T–cell memory is important to control persistent infections within the individual host and cannot be transmitted to offspring because of MHC polymorphism and MHC–restricted T–cell recognition. In contrast, antibody memory is transmissible from mother to offspring and may function essentially to protect offspring during the phase of physiological immuno–incompetence before, at and shortly after birth. This physiological immuno–incompetence is a result of MHC polymorphism and the dangers of the graft–versus–host and host–versus–graft reaction between mother and embryo, which necessitate immunosuppression of the mother and immuno–incompetence of the offspring. One may argue therefore that immunological memory of transmissible immunological experience is the basis on which MHC–restricted T–cell recognition could develop or coevolve.