Abstract: The present paper comments on the continuing debate in psychology as to therelative influence of maturation and experience in development. Attention is also givento the critical period concept, which supposes that biological and behavioral systemsare most open to environmental changes during early experience. The examplesdiscussed include visual space perception, handedness, Ianguage and sexual dimorphism.The relative importance of extrinsic as opposed to intrinsic determinants of develop-ment seems to vary from behavior to behavior. The claim that the effects of earlyexperience are irreversible may be valid for specific behaviors, but not generally. Moredetailed research is needed before basing educational practices on concepts such ascritical period.

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