Psychobiological studies of fetal ontogenesis in non-human species, particularly in laboratory rat, now have much to offer students of human development. Psychobiological approaches are 'ecologically' oriented which, for fetal research, implies consideration of the adaptive significance of behavior within the uterine habitat. Consistent with this orientation is a concern for the sensory capabilities of the fetus, especially in relation to the specific forms and levels of stimulation that occur within the uterine milieu. We describe recent advances in these areas, and the impressive range of fetal responses to naturally-occurring (often mother-induced) forms of sensory stimulation. To the psychobiologist, sensory-evoked responses of all kinds constitute the fetus' experience and much has been learned about the roles of such experience in regulating the rate, direction, and form of development. Indeed, experience can be considered a significant, if not neglected, mechanism of development. Finally, we briefly survey some contemporary analyses of the interrelations between developmental and evolutionary processes. We use onset of sensory function (which occurs in a stereotyped sequence in every vertebrate species for which there are data) as a developmental phenotype. Phylogenetic considerations of sensory development are discussed. By identifying and clarifying some of the intellectual questions that guide perinatal research with non-human species, we hope to improve the appreciation of novel insights and interpretive strategies that derive from different approaches. This is bound to enhance the study of human development and to improve the design and use of animal models.