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.

Do Animals have ideas? Do they experience pain like humans? Do they think about objects that they cannot see? About situations that have occurred in the past? Do they consciously make plans for the future or do they simply react unthinkingly to objects as they appear and situations as they arise? All of these questions have bearing on whether or not animals have consciousness. The advent of computers that ”think” has lead us to consider “intelligence” in a way we never (...) thought possible a decade ago. But when and how does information processing in the brain become automatic?In Minds of Their Own, Lesley J. Rogers examines the issue of animal thought both sympathetically and critically by looking at the different behavior characteristics of a variety of animals, the evolution of the brain and when consciousness might have evolved. To most people, to be conscious means to be aware of oneself as well as to be aware of others. But does this hold true for animals? The answer may have implications which transcend mere scientific inquiry: if animals are cognizant creatures, what, if any, moral responsibility do humans have to assure their rights? This timely book examines this issue and others by emphasizing comparisons between humans and animals: how we evolved; how we remember; how we learn. (shrink)

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)