Recent evidence in natural and semi-natural settings has revealed a variety of left-right perceptual asymmetries among vertebrates. These include preferential use of the left or right visual hemifield during activities such as searching for food, agonistic responses, or escape from predators in animals as different as fish, amphibians, reptiles, birds, and mammals. There are obvious disadvantages in showing such directional asymmetries because relevant stimuli may be located to the animal's left or right at random; there is no a priori association (...) between the meaning of a stimulus (e.g., its being a predator or a food item) and its being located to the animal's left or right. Moreover, other organisms (e.g., predators) could exploit the predictability of behavior that arises from population-level lateral biases. It might be argued that lateralization of function enhances cognitive capacity and efficiency of the brain, thus counteracting the ecological disadvantages of lateral biases in behavior. However, such an increase in brain efficiency could be obtained by each individual being lateralized without any need to align the direction of the asymmetry in the majority of the individuals of the population. Here we argue that the alignment of the direction of behavioral asymmetries at the population level arises as an “evolutionarily stable strategy” under “social” pressures occurring when individually asymmetrical organisms must coordinate their behavior with the behavior of other asymmetrical organisms of the same or different species. Key Words: asymmetry; brain evolution; brain lateralization; development; hemispheric specialization; laterality; lateralization of behavior; social behavior; theory of games. (shrink)

Honeybees show lateral asymmetry in both learning about odours associated with reward and recalling memory of these associations. We have extended this research to show that bees exhibit lateral biases in their initial response to odours: viz., turning towards the source of an odour presented on their right side and turning away from it when presented on their left side. The odours we presented were the main component of the alarm pheromone, iso-amyl acetate (IAA), and four floral scents. The significant (...) bias to turn towards IAA odour on the right and away from it on the left is, we argue, a lateralization of the fight-flight response elicited by this pheromone. It contrasts to an absence of any asymmetry in the turning response to an odour of the flowers on which the bees had been feeding prior to testing: to this odour they turned towards when it was presented on either the left or right side. Lemon and orange odours were responded to differently on the left and right sides (towards on the right, away on the left) but no asymmetry was found in responses to rose odour. Our results show that side biases are present even in the initial, orienting response of bees to certain odours. (shrink)

Indirect routes by which gonadal hormones influence sexual differentiation are considered. In rats, differentiation may depend on the way in which the mother responds to the hormonal condition of her pups, and this has implications for the interpretation of the data for humans. Interaction between gonadal hormones and light experience in chicks is compared with the mammalian systems covered in Fitch & Denenberg's review.

Parrots prepare for vocalization by a ventro-caudal retraction of the larynx. This laryngeal movement, which “frames” vocal sequences, is similar to a movement used by pigeons as a preparation for suction drinking. The air-pressure events involved in such movements can trigger either suction drinking or vocalization. This suggests a possible evolutionary link between these ingestive and vocal mechanisms.

The present response elaborates and defends the main theses advanced in the target article: namely, that in order to provide an evolutionary account of brain lateralization, we should consider advantages and disadvantages associated both with the individual possession of an asymmetrical brain and with the alignment of the direction of lateralization at the population level. We explain why we believe that the hypothesis that directional lateralization evolved as an evolutionarily stable strategy may provide a better account than alternative hypotheses. We (...) also further our discussion of the influence of stimulation and experience in early life on lateralization, and thereby show that our hypothesis is not deterministic. We also consider some novel data and ideas in support of our main thesis. (shrink)