migration

1. travel by nonhuman animals over relatively long distances to or from breeding areas. Migration is observed in birds, fish, and some mammals and insects (among others). In some species, it is seasonal, involving movement from a breeding area to an overwintering area; in others, particularly the salmon, it is observed only once in the lifetime of an individual. Factors influencing migratory behavior include chemical cues, pituitary or other hormones, relative change in day length, and temperature. See also migratory restlessness; navigation.

2. in the development of the nervous system, the movement of nerve cells from their origin in the ventricular zone to establish distinctive cell populations, such as brain nuclei and layers of the cerebral cortex.

Browse dictionary by letter

a b c d e f g h i j k l m n o p q r s t u v w x y z

Psychology term of the day

January 30th 2025

class theory

1. the notion that conflict between social and economic classes is a fundamental determining force in human affairs, affecting not only systems of government and social organization but also individual psychology. It is held that one’s perceptions, goals, and expectations, and even one’s conceptions of psychological health and illness, are heavily influenced by the class of which one is a member. Most modern manifestations of class theory trace their origins to Karl Marx, although the work of the critical theorists of the Frankfurt school (1930s onward) has also been influential. See Marxism.

2. the branch of set theory that is concerned with the properties of classes. It is particularly interested in defining the distinction between classes and sets that are not classes.