A `bright zone' in male hoverfly (Eristalis tenax) eyes and associated faster motion detection and increased contrast sensitivity

Eyes of the hoverfly Eristalis tenax are sexually dimorphic such that males have a fronto-dorsal region of large facets. In contrast to other large flies in which large facets are associated with a decreased interommatidial angle to form a dorsal `acute zone' of increased spatial resolution, we show that a dorsal region of large facets in males appears to form a `bright zone' of increased light capture without substantially increased spatial resolution. Theoretically, more light allows for increased performance in tasks such as motion detection. To determine the effect of the bright zone on motion detection, local properties of wide field motion detecting neurons were investigated using localized sinusoidal gratings. The pattern of local preferred directions of one class of these cells, the HS cells, in Eristalis is similar to that reported for the blowfly Calliphora. The bright zone seems to contribute to local contrast sensitivity; high contrast sensitivity exists in portions of the receptive field served by large diameter facet lenses of males and is not observed in females. Finally, temporal frequency tuning is also significantly faster in this frontal portion of the world, particularly in males, where it overcompensates for the higher spatial-frequency tuning and shifts the predicted local velocity optimum to higher speeds. These results indicate that increased retinal illuminance due to the bright zone of males is used to enhance contrast sensitivity and speed motion detector responses. Additionally, local neural properties vary across the visual world in a way not expected if HS cells serve purely as matched filters to measure yaw-induced visual motion

Art as an Indicator of Male Fitness: Does Prenatal Testosterone Influence Artistic Ability?

In his groundbreaking research, Geoffrey Miller (1999) suggests that artistic and creative displays are male-predominant behaviors and can be considered to be the result of an evolutionary advantage. The outcomes of several surveys conducted on jazz and rock musicians, contemporary painters, English writers ( Miller, 1999 ), and scientists ( Kanazawa, 2000 ) seem to be consistent with the Millerian hypothesis, showing a predominance of men carrying out these activities, with an output peak corresponding to the most fertile male period and a progressive decline in late maturity. One way to evaluate the sex-related hypothesis of artistic and cultural displays, considered as sexual indicators of male fitness, is to focus on sexually dimorphic traits. One of them, within our species, is the 2nd to 4th digit length (2D:4D), which is a marker for prenatal testosterone levels. This study combines the Millerian theories on sexual dimorphism in cultural displays with the digit ratio, using it as an indicator of androgen exposure in utero. If androgenic levels are positively correlated with artistic exhibition, both female and male artists should show low 2D:4D ratios. In this experiment we tested the association between 2D:4D and artistic ability by comparing the digit ratios of 50 artists (25 men and 25 women) to the digit ratios of 50 non-artists (25 men and 25 women). Both male and female artists had significantly lower 2D:4D ratios (indicating high testosterone) than male and female controls. These results support the hypothesis that art may represent a sexually selected, typically masculine behavior that advertises the carrier's good genes within a courtship context

Doctor of Philosophy

dissertationSex differences in spatial ability and navigation are well documented. Although several theories explain a subset of these findings, a comprehensive theory has yet to be offered and tested. As such, we provide evidence that co-occurring evolutionary pressures shaping male and female range sizes lead to the use of different navigation strategies, which produce differences in self-reported spatial anxiety and sense of direction. Next, we provide experimental evidence testing two important implications of our model. First, if the co-occurring evolutionary pressures producing differences in range size are functional, then they ought to shape how males and females explore a novel environment. In our experiment, males demonstrated a higher rate of diffusion than females (e.g., spreading throughout the space more quickly), and females demonstrated more caution while exploring a novel, large-scale virtual environment. Second, maintaining a larger range size places greater demands on male navigation, which not only leads to the use of a different navigation strategy, but also to better navigation performance. At first glance, there is inconclusive evidence in support of superior male navigation ability. A closer look reveals that sex differences in navigation often emerge when individuals are allowed to freely explore the environment prior to testing. Given the expected sex differences in exploration behavior predicted by our model, we provide evidence that features characteristic of male exploration also offer the individual a wealth of spatial information that may lead to better navigation performance

A hundred years of debates on sex differences: developing research for social change

After women secured the right to vote some hundred years ago, the assertions about their innate inferiority gradually began to vanish, giving way to theories about the countless aspects which apparently differentiated them from men. In this paper, we follow the evolution of research on sex differences, starting with the work of the first female psychologists who questioned the theories that justified women’s subordinate positions in society. We trace the main developments of the studies on sex differences, their relationship with social roles, gender stereotypes, and gender identity, and describe the strategies used to highlight the role of society rather than of biology in shaping men and women’s personalities and behaviors. We describe the controversies this area of research gave rise to, the debates over its political implications, and the changes observed over time in women’s social positions and within research perspectives. Finally, we discuss the mutually reinforcing effects of social organization and lay conceptions of gender and reflect on how the field of research on sex differences has contributed to building a fairer society

The dimensions of personality in humans and other animals: A comparative and evolutionary perspective

This paper considers the structure and proximate mechanisms of personality in humans and other animals. Significant similarities were found between personality structures and mechanisms across species in at least two broad traits: Extraversion and Neuroticism. The factor space tapped by these personality dimensions is viewed as a general integrative framework for comparative and evolutionary studies of personality in humans and other animals. Most probably, the cross-species similarities between the most broad personality dimensions like Extraversion and Neuroticism as well as other Big Five factors reflect conservative evolution: constrains on evolution imposed by physiological, genetic and cognitive mechanisms. Lower-order factors, which are more species- and situation-specific, would be adaptive, reflecting correlated selection on and trade-offs between many traits

Sex differences in the development of spatial behavior in montane voles : experiential and hormonal influences

In animals with polygamous mating systems, in which males' territories overlap the territories of two or more females, males perform spatial tasks with fewer errors than do females. While it has been suggested that these differences persist due to natural selection, this does not explain how they develop. In this study, I investigated the development of sex differences in spatial abilities of montane voles (Microtus montanus), a polygamous species, as influenced by environmental and hormonal factors. Litters were culled to three same-sex pups and raised in clear plastic cages, either small (21x20x23cm = Restricted) or large with objects for exploration (21x38x48cm = Expanded) . The pups were weaned at 21 days of age and remained in their natal environment

A quantitative analysis of the effects of chess instruction on the mathematics achievement of southern, rural, black secondary students

This study investigates the effects of chess instruction on the mathematics achievement of a group of southern, rural, black, secondary students. Instruments used included the mathematics section of the CAT (Level 20), Group Embedded Figures Test (GEFT), Matrix Analogies Test-Short Form (MAT-SF), Guilford-Zimmerman Spatial Visualization Test (SV), and Guilford Zimmerman Spatial Orientation Test (SO). The treatment group, which received 18 weeks of chess instruction, consisted of 11 females and 8 males. The control group was comprised of 10 females and 10 males. All participants were high school juniors or seniors. Analysis of variance of the pre-tests found no significant differences between the treatment and control groups. Post-test data were analyzed by 2 x 2 MANCOVA which used statistically significant pre-tests as covariates. The treatment group scored significantly higher than the control group on post-test measures of mathematics achievement, F(1, 38) = 4.14, $p \u3c .043;$ field dependence/independence, F(1, 38) = 6.02, $p \u3c .019;$ spatial visualization, F(1, 38) = 14.13, $p \u3c .001;$ and nonverbal reasoning, F(1, 38) = 6.09, $p \u3c .037.$ The control group scored significantly higher on the spatial orientation test, F(1, 38) = 4.22, $p \u3c .048.$ Further analysis by one-way ANCOVA found that only female members of the treatment group scored significantly higher on measures of mathematics achievement. Factor analysis extracted only one variable from the five instruments used in the study. This variable was labeled Spatially Based Cogntion (SBC). One-way ANCOVA of this extracted variable also found that only the treatment group females scored significantly higher than the control group females. No significant difference was found between the treatment group males and control group males for the extracted variable