1. The present position of some of the ideas due wholly or in part to Lorenz is discussed. These concepts include imprinting, the fixed action pattern, innate releasing mechanisms, etc. Imprinting is now seen as a special case of the process of perceptual learning and as such has become a major interest of learning psychologists. The study of F. A. P. and I. R. M. is stressed as providing — the one on the motor, the other on the perceptual side — an important avenue of approach to the problem of quantifying the degree of behavioural complexity coded in the genome.
2. The importance of information theory as supplying the principles of a method for quantifying the complexity of biological systems is stressed. This extends equally to anatomical, physiological and behavioural complexity. The problem of increase of information during the evolution of life is compared with that during the development of the individual from the zygote.
3. It is suggested that information theory helps to make clear three of the prime functions and aims of ethology, namely: 1. To differentiate between complexity coded in the germ plasm (the truly innate components) and that impressed by the environment (imprinted or otherwise learned). 2. To quantify the innate components. 3. To quantify the learned components.
4. Present views on the method of coding information in the genome are briefly summarised. Difficulties due to the loss of information by thermal noise in ultra-microscopic systems are considered. The problem and significance of redundancy in coding are briefly discussed.
5. It is suggested that modern work on macromolecular coding will bring new light on old disputes such as mechanism versus vitalism and prefor-mationism versus epigenesis.
6. The problem of the acquisition and storage of information by the nervous system during ontogeny is briefly considered. It is argued that there are as yet no valid grounds for assuming that the method employed by the nervous system is based on any mechanism similar to that employed by the genome.
7. Elsasser's “Principle of Finite Classes” is referred to and some of its implications briefly considered.