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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 17, Issue 4, 2004


Uniqueness, Diversity, Similarity, Repeatability, and Heritability

This paper reexamines classic attempts at estimating the number of possible genotypes for a species. In the original computations (Hirsch, 1963), the probability that any two human parents will produce two offspring with the same genotype was calculated to be equal to (1/223)2, or over one chance in 70 trillion. The error lies in that this number reflects the number of cells in the matrix of zygotes, not the number of zygotic genotypes. When this is taken into account, the probability of two human parents producing two offspring with the same zygotic genotype is 1 in 160,000—almost a billion times more likely than previously suspected. The complexity of the genetic system is also discussed in the context of the concept of “heritability,” often confused with that of “heredity.” This confusion has led to the wrong view that heritability represents a nature/nurture ratio.

Changing Odor Hedonic Perception Through Emotional Associations in Humans

A long-standing debate in olfactory perception is whether hedonic responses to odors are learned or innate. To test the hypothesis that olfactory hedonic responses are acquired through associative learning with emotion, two experiments were conducted that varied with regard to whether a novel (“target” odor) was pre-experimentally pleasant or unpleasant and the emotional association was positive or negative. Participants were randomly assigned to an Experimental Group (odor + emotional association) and various Control Groups. Evaluations of the target odor and several common odors that were not explicitly part of the association procedures (anchor odors) were made: prior to the manipulations, postmanipulation, 24 h after the manipulation, and 1 week from the start date. In both experiments, evaluation of the target odor by all participants was comparable at premanipulation and responses to the anchor odors were unaffected by time or experimental condition. However in each experiment, post-emotional manipulation ratings to the target odor were significantly altered in the Experimental Groups and showed that odor perception had changed in accord with the emotional valence of the associated experience. These findings support the hypothesis that olfactory hedonic responses are learned through emotional associations and raise new methodological and theoretical questions for future research.

Sex-related Responsiveness to Changes in Tactile Stimulation in Hooded Rats

Hooded rats were allowed to choose between a Y-maze arm in which the floor had tactually changed, and an unchanged arm. This change was from either two rough (or smooth) arms to one smooth and one rough, or the reverse sequence, following 6- or 12-min acquisition trials. All rats were able to distinguish between the changed and the unchanged arms irrespective of the type of change. Males were less responsive to the novel arm after 12-min (possibly aversive) trials. They later emerged more slowly from a darkened chamber into a brightly lit arena, than equivalent females. For all rats, responsiveness to tactile change was positively correlated with emergence latencies. Fewer first entries of the more novel of two brightly illuminated Y-maze arms suggested disruption of responsiveness to change by an aversive experience.

Pre- and Postconflict Interactions Between Female Japanese Macaques During Homosexual Consortships

In this paper, I examine whether homosexual behavior in female Japanese macaques functions to reconcile conflicts following the outbreak of aggression. Contrary to the predictions of the reconciliation hypothesis, homosexual interactions between female Japanese macaques did not peak during postconflict periods, as compared to matched control periods preceding the conflicts. In fact, aggressive interactions appeared to inhibit, rather than facilitate, the expression of homosexual behavior among subordinate consort partners. Alternative proximate and ultimate explanations for female homosexual behavior in Japanese macaques are presented.

Shortcut taking by ferrets (Mustela putorius furo)

A 2 X 2 between-subjects design was used to test for the tendency of domestic ferrets to take novel shortcuts. The cross maze with shortcuts adapted by Poucet (1985) was used to train ferrets to search for a goal (an empty food bowl) while having the possibility of seeing the shortcuts or not during training (i.e., a screen, which was either transparent or opaque, blocked off the shortcut). In the test sessions in which the animals were given access to the shortcuts, the goal was visible for half of the subjects in each training condition and not visible for the other half. Ferrets were more likely to take the shortcut if they had seen it during training, regardless of whether they could see the goal or not during the test: Visual familiarity with the shortcut is sufficient to account for shortcut taking. When the goal was not visible and the shortcut had not been seen prior to the test, performance was no different from chance: There was no evidence for the ability to infer a shortcut. Pronounced individual differences were obtained when the shortcut was visually unfamiliar yet the goal was visible.

Pigeon’s Behavior as a Discriminative Stimulus

This study examined whether stimulus control by a conspecific’s behavior generalizes to a different location and whether this behavior is maintained in the presence of a new conspecific. Three pigeons were trained to peck a key opposite to that on which another pigeon, the ”stimulus bird,” was pecking. After training with 2 keys, the third key was introduced. Generalization to this new key position was incomplete although one bird responded to this key during the first session and the other two birds showed some evidence of facilitation by the behavior of the stimulus bird. Next, having confirmed that experimental birds used only the stimulus bird’s behavior as a cue to key choice, a new stimulus bird was introduced. All experimental birds correctly responded in its presence indicating that the control was not specific to the individual in the presence of which training occurred.