Is two times a half more than one? Function and evolution of brain lateralization in animals and humans

Brain lateralization refers to the intriguing phenomenon that the two hemispheres differ in structure and in functional output. Brain lateralization has profound implications for the organization of cognition, emotion, and behaviour. Until recently it was thought to be a unique property of humans and the exclusive domain of psychology. Recent research by biologists revealed functional lateralization in all 5 classes of vertebrates, and discovered tools to manipulate the development of lateralization in some species, particularly birds. This opens the possibility to test hypotheses about the function and evolution of brain lateralization. This has not yet been undertaken in human subjects, due to the lack of crosstalk between psychology and biology. We propose an interdisciplinary twinning project, focussing simultaneously on an animal model, the pigeon, and on humans, to test the function and evolution of brain lateralization. We will address the following questions: 1: To what extent is the development of brain and behavioural lateralization plastic? This will be approached in birds by experimental manipulation of embryonic exposure to light, due to asymmetrical head position, and of prenatal exposure to steroid hormones, and in humans by correlating the direction and degree of lateralization with head position in babies, and with prenatal exposure to steroid hormone levels; 2: Is lateralized function advantageous in terms of Darwinian fitness at the level of the individual? We aim at answering this question by testing in the pigeon the effect of manipulation of brain asymmetry on survival and reproduction under field conditions, and in humans by correlating the direction and degree of lateralization with fitness measurements such as socio-economic status, health and number of offspring obtained in a society that until recently lived in a pre-industrial condition; 3: Does lateralization enhance efficient processing? This will be addressed by applying in both the pigeon and humans specific ecologically relevant dual tasks; 4: Can frequency dependent selection explain a bias in lateralization at the level of the population? We evaluate the potential for frequency dependent selection for left and right hemispheric dominance in agonistic interactions (combatant sports in humans, aggressive interactions in pigeons).