A model for the development of this mechanism is offered as well as evidence for it from five areas: (1) the nature of the association of early attachment and later cognitive functioning, (2) accumulating evidence for the association between secure attachment and the facility with which internal states are understood and represented, (3) the limited predictive value of early attachment classification, (4) the studies of the biological functions of attachment in other mammalian species, and (5) factor analytic studies of adult attachment scales that suggest the independence of attachment type and attachment quality. The author tentatively proposes that attachment in infancy has the primary evolutionary function of generating a mind capable of inferring and attributing causal motivational and epistemic mind states, and through these arriving at a representation of the self in terms of a set of stable and generalized intentional attributes thus ensuring social collaboration, whereas attachment in adulthood serves the evolutionary function of protecting the self representation from the impingements that social encounters inevitably create. Severe personality pathology arises when the psychological mechanism of attachment is distorted or dysfunctional and cannot fulfill its biological function of preserving the intactness of self representations.RESUMEN: A partir de las siguientes cinco áreas, ofrecemos un modelo para el desarrollo de este mecanismo, así como prueba del mismo: (i) la naturaleza de la asociación entre la temprana afectividad y el funcionamiento cognitivo posterior, (ii) la acumulación de pruebas para determinar la asociación entre una afectividad segura y la facilidad con la cual los estados internos son comprendidos y representados, (iii) el limitado valor de predicción de la clasificación de la temprana afectividad, (iv) los estudios de las funciones biológicas de la afectividad en otras especies mamíferas, y (v) los estudios analíticos de factores de las escalas de la afectividad adulta que sugieren la independencia del tipo y calidad de la afectividad. El autor propone tentativamente que la afectividad en la infancia tiene como función primaria de evolución la de generar una mente capaz de deducir y atribuir estados mentales causales, de motivos y de conociPaper submitted to the Infant Mental Health Journal February 2001, based on a plenary address given at the World Association of Infant Mental Health Congress, Montreal, July 28, 2000. The author would like to acknowledge the contribution of his colleagues at the Child and Family Center, Menninger Clinic, Topeka, Kansas. This article is in large part based on data gathered by them. In particular, the author is indebted to Drs. Helen Stein, Jon Allen, Martin Maldonado, and Jim Fultz. The author would also like to acknowledge Dr. Anna Higgitt's guidance in the writing of the paper. This article is part of an ongoing collaboration with Drs. Mary Target, George Gergely, and Elliot Jurist. A coauthored book covering these themes has recently ...