Contemporary brain morphology in ecological and ethological perspectives

The use of ethological, along with morphological data is presented as a general realistic approach to the understanding of the vertebrate nervous system. While the brain/body size relation, either in ontogeny or phylogeny, is still a mandatory method for describing brain evolution, the interpretation of the allometry equation remains subject to difficulties. A mixed quantitative-qualitative relationship between brain and behaviour is defined through the new concept of cociation. Results based on this approach are presented for a number of mammals having a broad variety of sizes and life-habits. The necessity of using brain components, and not only total brains, is emphasized. The functional aspects of relative brain and brain component size, especially with reference to metabolism and behaviour, are commented upon. These aspects require a cautious handling of the causality principle, and a particular conception of progress in brain evolution. The study of brain components in a functional perspective has been characterized, in recent years, by remarkable advances in modular morphology. These are summarized and it is suggested that they might lend themselves to especially significant behavioural correlations. A hypothetical model for a two-level brain, involving both redundancy and configurations, and consistent with a neuroethological approach, is recommended as a potentially promising direction for future progress in brain morphology, in ecological and behavioural perspectives.