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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 14, Issue 1, 2001


The Inevitability of Evolutionary Psychology and the Limitations of Adaptationism: Lessons from the other Primates

The arrival of Evolutionary Psychology (EP) has upset many psychologists. Partly, this reflects resistance to what is perceived as genetic reductionism, partly worry about yet another step closer to the life sciences. Are the life sciences going to devour the social sciences? This essay starts out with a list of pitfalls for the beginning Darwinists that many EP followers are, warning against simplistic adptationist scenarios, and the fragmentation of the organism, the human brain (a module for every capacity), and the genome (a gene for this and a gene for that). Despite these criticisms, the author is generally sympathetic to the evolutionary approach, however, and feels that EP is inevitable. It may show growing pains, but psychology does need to move under the evolutionary umbrella, which is the only framework that can provide coherence to a fragmented discipline. The essay concludes with several illustrations of the usefulness of evolutionary theory to explain the social behavior of primates. Primatologists face many of the same dilemmas as followers of EP in that primate behavior seems almost endlessly variable. Examples of political strategy, peacemaking, and reciprocal exchange show the complexity, the profound similarity to human behavior, and the promise of the evolutionary framework.

Social Influences on Food Choices of Norway Rats and Mate Choices of Japanese Quail

Here I review the two major lines of research in which my laboratory has been engaged for the past 35 years. The first of these research programs concerns the description and analysis of social learning processes influencing food choices of Norway rats ( Rattus norvegicus ). The second involves social interactions affecting mate choices of Japanese quail ( Coturnix japonica ). Study of these model systems has shown that at least two biologically important behaviors, food choice and mate choice, can be shaped by social interactions and that the social interactions that bias behavioral development are open to reductionist analysis in terms of the behavior of interacting individuals.

Some Parameters of Stimulus Preexposure that Affect Conditioning and Generalization of Taste Aversions in Infant Rats

The effects of stimulus preexposure on conditioning and generalization of a taste aversion were evaluated in infant rats, manipulating stimulus similarity and duration, and the length and procedure (intermixed vs. blocked) of preexposure. Preexposure to simple tastes retarded conditioning and reduced generalization (Experiment 1a), whereas preexposure to compound tastes facilitated conditioning and increased generalization (Experiment 1b). Increasing the number of preexposure trials retarded conditioning and decreased generalization with compound tastes (Experiment 1c). These experiments failed to find a differential effect of intermixed vs. blocked stimulus preexposure. In Experiment 2, a 15 min exposure to the conditioned stimulus during conditioning resulted in a weak aversion, whereas a 60-min exposure resulted in a strong aversion. In Experiment 3, the strength of the aversion and the duration of the conditioned stimulus were directly related in nonpreexposed pups, but inversely related in preexposed pups. In infant rats, the level of generalization between stimuli is determined by how preexposure affects acquisition rate.

Effects of Increasing the Time to Reinforcement on Interval Timing in Rats

The experiment examined interval timing in rats during a momentary, unsignaled, increase in the time to reinforcement. A session began with intervals programmed according to a fixed interval (FI) 60 s reinforcement schedule, changed to either an FI 90 s, FI 120 s, or FI 180 s schedule at an unpredictable point, and then returned to an FI 60 s schedule after 1, 8, or 24 successive long intervals had elapsed. Overall, postreinforcement wait time duration increased with increases in the scheduled time to reinforcement. The amount by which wait time increased did not depend on the duration of longer intervals, but did depend on the number of longer intervals intercalated into a session. The results indicate that rats are sensitive to moment-by-moment changes in the time to reinforcement and support other studies showing an asymmetry between timing upward and downward shifts in the criterion for reinforcement of an FI schedule.

Use of Spatial Dimensions in Pattern Discrimination and Similarity Judgments by Pigeons

Two experiments examined the role of spatial dimensions in pattern discrimination and judgment of similarity by pigeons. In Experiment 1, pigeons were given a symbolic matching-to-sample task in which they first learned to discriminate between two patterns (A and B) that differed in the spatial layout of an arrow inside a circle divided into four quadrants. The first training stimulus contained an arrow inside the Top Left quadrant and the tip of the arrow was pointing toward 90 degrees. The second training stimulus contained an arrow inside the Bottom Left quadrant and the arrow was pointed downwards at 180 degrees. Fourteen new patterns, consisting of all the remaining combinations of arrow orientations and arrow locations (quadrants), were then presented and their categorization by the pigeons was examined. The results showed that the two dimensions pertaining to the position of the arrow (Top/Bottom and Left/Right halves of the circle) and their interactions were more salient than the two dimensions pertaining to its orientation (Horizontal / Vertical arrows and two arrow ends). Experiment 2 showed that the position of a pattern component was encoded and used in similarity judgments even when the A and B differed along nonspatial dimensions (a rectangle vs a circle). When pigeons encountered new visual patterns and judged their similarity to old ones, they privileged the position of the pattern components over shape in their judgments.