The genetic architecture of a trait may be uncovered by using quantitative genetic .... evolutionary history of stabilising selection for exploration. 2.2.2. ... against the wall; standing on its hind legs, the mouse places one or two forepaws ..... The experiment reviewed here auempts to provide answers to the following questions.
NATURAL SELECTION ON HIPPOCAMPAL CIRCUITRY UNDERL YING EXPLORATORY BEHAVIOUR IN MICE: QUANTITATIVE-GENETIC ANALYSIS
W.E. CRUSIO Getlerique, Neurogetzeriqu(! et Comportement, URA 1294 CNRS, UFR Biomedicale. Universite Rene Descartes (Paris V), 45 rue des Saints-peres, F-75270 Paris Cedex 06, France
1. Introduction Behaviour is an animal's way of interacting with its environment and it is therefore a prime target for natural selection. As behaviour is the output of an animal's nervous system, this indirectly leads to selection pressures on neuronal structures. In consequence, each species' behaviour and nervous system have co-evolved in the context of its natural habitat and can be properly comprehended only when their interrelationships are regarded against that background [7J. This notion implies that 10 arrive al a profound understanding of neurobehavioural traits, one will have to consider problems of causation. Van Abeelen [59) distinguished between the phenogenetic and the phylogenetic aspects of causation. Both concern the genetic correlates of neurobehavioural traits, the first in a gene-physiological, the lauer in an evolutionary sense. Stated otherwise, neurobehavioural geneticists attempt to uncover the physiological pathways underlying the expression of a trait and to provide an answer to the question of what exactly is the adaptive value of this trait for the organism. As I have argued before [12,13], quantitative-genetic methods may be employed with profit to address problems related to both aspects of causation. As an illustration of this research strategy. I present here the results of some experiments concerning mouse exploratory behaviour and hippocampal neuroanatomy. 2. The Ph)'iogenetic Aspect of Causation 2.1. NATURAL SELECTION AND GENETIC ARCHlTECTURE Selection pressures mould the species' genetic make-up which consequently will show traces of this past selection. Therefore. information about the genetic architecture of neurobehavioural traits might permit us to make inferences about the evolutionary history of these traits [5). In iL
