The hypothesis presented is a development of that set forth by William James, in his Principles of Psychology. Sketched out by James, it can now be more fully developed, thanks to half a century of research on learning. The general principles very likely account for most of the importance of early experience to pheno-typical behaviour.
Imprinting is regarded as simple stimulus-response learning occurring under somewhat special conditions. An initial weak tendency to follow moving objects of specifiable size is strengthened by repetition of the following behaviour. This following behaviour becomes restricted to a specific class of object by a later-appearing species-specific tendency to fear and to escape from objects of the same general class as that which initially excited following. Only the class of objects that the animal has had extensive practice in following; the animal remains “tame” with respect to it. This sparing is a case of the transfer phenomenon called proactive inhibition in other contexts.
When adult behaviours appear, proactive inhibition should lead to interference (by persisting fear and flight components of behaviour) with response to those objects that had not been followed prior to the appearance of the fear and flight behaviour in the animal’s early days.
The hypothesis is consistent with data that have appeared in the literature, and provides a basis for interpreting it. It also suggests that further experiments will reveal specific relationships between the strength of following behaviour in the young animal, and the strength of imprinting observable in the adult. It suggests analyses of the complex and apparently conflictful components of courtship and mating.
According to it, imprinting, as it has been found (and studied intensively) in some species of birds should be found in all social species whose young can walk or swim shortly after birth or hatching; and that it should not be clearly evident in those species whose young are not capable of locomotion through their first weeks or months of life.