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Lorenz, Konrad (Zacharias) (b. November 7, 1903; d. February 27, 1989), Austrian
psychologist. Lorenz’s research laid the foundations for a new scientific discipline called
ethology, the systematic observation, recording, and analysis of animal behavior.
Ethology emphasizes the role of objective and quantifiable observations of behavior and
the need to integrate the study of its multiple aspects: physiological or cognitive
mechanisms regulating it, changes related to age, its contribution to an individual’s
survival and reproduction, and its evolutionary history. Although ethology is often
equated with the study of animal behavior, it has made many important contributions to
understandings of human behavior and development.
Lorenz shared the Nobel Prize in 1973 for elucidating the importance of critical
periods. A critical period is a restricted time window in the life of an individual during
which specific events must occur to ensure normal development. The same events
occurring before or after the critical period will have little or no effect on development.
Lorenz observed that young birds exposed to a human being shortly after hatching
become “imprinted”: they will follow this individual everywhere and later in life will
direct sexual behavior toward this individual instead of members of their own species.
Later work showed that young birds can be imprinted not only on humans but also on
other animals or even inanimate objects, that imprinting is stronger in some species of
birds than in others, and that the process is not as irreversible as Lorenz had originally
thought. The notion of critical periods has since been replaced with that of sensitive
periods, which are viewed as periods of time with relatively flexible boundaries in which
developing organisms are most responsive to certain environmental stimuli and most
