Ecology comprises many topics, but is conveniently divided in respect of the laws governing the physiology of animals, populations, and the communities or the interactions of populations. Behaviour is not restricted to individuals alone. It also extends to the behaviours between individuals of the same species as well as the behaviours between individuals and populations of different species. The primary behavioural categories are those relating to reproduction, sustenance, development and survival which involve intra- and inter-species competition as well as the influence of the abiotic and biotic environment. Behaviour is a phenotypic expression of the interaction of the genotype (of individuals or species) with the environment. This expression evolves from the stimuli that motivate animals to an inborn activity, such as the sucking response of the calf upon contacting the teat of the cow, or a learned or practiced activity, such as coital attempts by inexperienced bulls and the competent performance of the experienced bulls. Man observes behaviours of animals and infers a cause or reason. Such inference must derive from a full knowledge of the behaviour and of the variability of the behaviour of species — a knowledge that is gained after much work and over an extended time. Interestingly, man's observations and inferences are species-specific behaviours which also have a variability in performance. Man's evolution from the hunter behaviours to the recent husbandry behaviours must have involved much change in concepts, namely a revolution in behaviour and perceptions. Man is presently in a state of evaluating again his relationship to other species of animals in respect of his perceptions of animal welfare and the ethology of animal life.