Steven J. C. Gaulin

Spatial memory and adaptive specialization of the hippocampus

The hippocampus plays an important role in spatial memory and spatial cognition in birds and mammals. Natural selection, sexual selection and artificial selection have resulted in an increase in the size of the hippocampus in a remarkably diverse group of animals that rely on spatial abilities to solve ecologically important problems. Food-storing birds remember the locations of large numbers of scattered caches. Polygynous male voles traverse large home ranges in search of mates. Kangaroo rats both cache food and exhibit a sex difference in home range size. In all of these species, an increase in the size of the hippocampus is associated with superior spatial ability. Artificial selection for homing ability has produced a comparable increase in the size of the hippocampus in homing pigeons, compared with other strains of domestic pigeon. Despite differences among these animals in their histories of selection and the genetic backgrounds on which selection has acted, there is a common relationship between relative hippocampal size and spatial ability.

Effects of gender and sexual orientation on evolutionarily relevant aspects of human mating psychology

Sexual selection theory provides a powerful model for the analysis of psychological sex differences. This research examined (a) tests of several sex differences in mating psychology predicted from sexual selection theory, (b) broad developmental hypotheses about sex differences in mating psychology--through the relationship of mating psychology to sexual orientation, and (c) the structure of within-sex differences in mating psychology. Scales measuring aspects of mating psychology were administered to heterosexual and homosexual Ss of both sexes. The structure of scale intercorrelations was similar across groups. All scales yielded sex differences consistent with sexual selection theory. Homosexual Ss generally obtained scores similar to those of same-sex heterosexual Ss, though several scales were significantly related to sexual orientation. Findings constrain hypotheses concerning the origins of sex differences.

Sex Differences in Spatial Ability: An Evolutionary Hypothesis and Test

A comparison of male and female home-range size and maze performance in two congeneric species of microtine rodents suggests an evolutionary explanation for sex differences in spatial ability. Male/female differences in this cognitive trait seem to depend ultimately not on sex per se, but rather on the type of mating system and on the associated reproductive tactics employed by each sex. Through a combined field and laboratory study, the hypothesis that males evolve superior spatial ability only when they are more mobile (i.e., have larger home ranges) than females is developed and tested.

Sexual selection for spatial-learning ability

Sex differences in spatial learning have been thought to be universal among mammals, but their adaptive significance has been neglected. Spatial-learning skills are hypothesized to evolve in proportion to nagivational demands, and it is predicted that sex differences in spatial ability will evolve only in species where range expansion contributes differentially to the reproductive success of males and females. This prediction was tested via field studies of ranging behaviour and laboratory studies of spatial ability in two congeneric rodent species whose mating systems differ. Radiotelemetric studies showed that, in a polygynous species (meadow voles, Microtus pennsylvanicus), males expanded their ranges only during the breeding season and only when they attained full reproductive status. Females showed neither response. This suggests that range expansion was a male reproductive tactic. In contrast, a monogamous congener (prairie voles, M. ochrogaster) showed no sex differences in ranging, regardless of reproductive status. This probably reflects the relative inability of monogamous males and females to benefit from increased exposure to members of the opposite sex. When subsequently tested in a series of seven symmetrical mazes, subjects from the field studies exhibited the predicted sex-by-species patterns of spatial ability: only meadow voles showed consistent male superiority on these spatial tasks.

Superior spatial memory of women: Stronger evidence for the gathering hypothesis

Abstract Male and female college students played the commercial game Memory TM , which required them to recall the location of previously viewed items, and also completed a 20-item mental rotation task. As is typical, males performed better than females ( d = .67) on the mental rotation task. In contrast, females outperformed males by a large margin ( d = −.89) on the memory task. Performance on the two tasks was correlated for females, but not for males. The reversal of sex differences between tasks suggests that spatial ability is not a unitary trait and that different kinds of spatial processing may have been important for males and females in the EEA (environment of evolutionary adoptedness). The Memory TM game appears to mimic the cognitive demands of foraging better than previous spatial memory tasks.

Behavioral ecology ofAlouatta seniculus in Andean cloud forest

The behavior and ecology ofAlouatta palliate àre well studied; we report here on the first long-term study of anotherAlouatta species, the red howler monkey,A. seniculus. AlthoughA. seniculus was studied at a high elevation in the Colombian Andes, it exhibits many behavioral and ecological similarities to lowlandA. palliata. Continuous focal sampling indicates thatA. seniculus spends 78.5% of its time resting, 5.6% moving, and 12.7% feeding. It has a day range of 1.09 km and a home range of 22 ha. Like its more northern relative,A. seniculus spends more than 50% of its feeding time on leaves–especially young leaves–but on a dry-weight basis, fruits comprise the majority of its diet. The small home and day ranges observed as well as the large amounts of time spent resting are all argued to be aspects of a relatively folivorous foraging strategy. Daily food intake is estimated to be 1.23 kg fresh weight (0.266 kg dry weight). Foraging efficiency (yield/time) varies by a factor of almost 6 across major food types, with item size and distribution being the key determinants. Food preferences change markedly over the activity period, with high-energy sources predominating early and high-protein sources late.

Matrilateral biases in the investment of aunts and uncles : A consequence and measure of paternity uncertainty.

In a study of the kin investment of aunts and uncles we show that the laterality effect expected as a result of paternity uncertainty is statistically reliable but somewhat smaller than the sex effect. Matrilateral aunts invest significantly more than patrilateral aunts, and the same is true for uncles. Regardless of laterality, however, aunts invest significantly more than uncles. Multivariate controls show that the matrilateral bias is fully independent of any age or distance confounds that might result from sex differences in age at marriage or dispersal. We discuss our results in relation to recent findings on the kin investment of grandparents (Euler and Weitzel 1996). In addition, we propose a simple method for estimating the level of paternity uncertainty from kin investment data; application of this method to our data on aunts and uncles suggests that between 13% and 20% of children are not the offspring of their putative father. Our parallel analyses of Euler and Weitzel’s (1996) data on grandparental investment suggest a similar estimate, that paternity uncertainty lies between 9% and 17%.

Sexual Dimorphism in Weight Among the Primates: The Relative Impact of Allometry and Sexual Selection

In this paper, we examine allometric and sexual-selection explanations for interspecific differences in the amount of sexual dimorphism among 60 primate species. Based on evidence provided by statistical analyses, we reject Leutenegger and Cheverud’s [(1982). Int. J. Primatol.3:387-402] claim that body size alone is the major factor in the evolution of sexual dimorphism. The alternative proposed here is that sexual selection due to differences in the reproductive potential of males and females is the primary cause of sexual dimorphism. In addition, we propose that the overall size of a species determines whether the dimorphism will be expressed as size dimorphism,rather than in some other form.

A Jarman/Bell model of primate feeding niches

Some of the behavioral-ecological variation in the primate order can be explained by reference to a general model known as the Jarman/Bell principle. This principle involves a scaling relationship between metabolism and body size which suggests that body size is a fundamental tactic in an animals feeding strategy. Relatively accurate predictions regarding the diets of primates of known body weight follow from this model. In addition, it can be expanded to predict the kinds of adaptations that would appear in animals that deviate from the expected size/diet pattern. The model is general enough such that, when joined with feeding strategy theory, it can be applied to extinct organisms. In this context it is suggested that Pleistocene hominid ecology was characterized more by omnivory than carnivory.

Matrilateral biases in the investment of aunts and uncles

Gaulin, McBurney, and Brakeman-Wartell (1997) found that college students reported both matrilateral and sex biases in the investment of aunts and uncles (aunts invested more than uncles). They interpreted the matrilateral bias as a consequence of paternity uncertainty. We replicated that study with Orthodox Jewish college students, selected because they come from a population we presume to have higher paternity certainty than the general population. The Orthodox sample also showed matrilateral and sex biases. Comparing the two data sets, the Orthodox sample reported more investment, and slightly less matrilateral and sex biases, but the differences were not statistically significant. We did find an interaction between sex of relative and group membership, resulting from greater investment by Orthodox uncles. We interpret the results as reflecting the operation of a facultative investment mechanism whose upper limit is tuned to the maximum levels of paternity certainty found in ancestral environments. Lack of a difference in matrilateral bias between groups may result from levels of paternity certainty near to, or above, that maximum in both groups.