A study of the shoulder architecture of the sheep involving a comparison between the Romney and Cheviot breed types : being a thesis presented in partial fulfillment of the requirements for the degree of M. Agr. Sc. from the University of New Zealand, 1952
In the wild state, the body form of ungulates is determined by two factors:- (1) the animal's necessity to cover ground in search of food and to escape its enemies and (2) its need to convert efficiently the food it obtains into energy for its maintenance and for the performance of the first factor. Another set of environmental responses, those incidental to the perpetuation of the race, appear to have but little influence on the bodily form of the ungulate (Howell, 1944). Hence, in the main, the musculature, skeleton, internal organs and the distribution of fat deposits in such species as the wild cattle or the wild sheep in their evolutionary response to environment would be governed by locomotive demands and the form from which a new adaptation evolved. As pointed out by Simpson (1949):- "in the evolution of a species..... the surviving organisms must meet the minimum requirements of life in an available environment and changes can only occur on the basis of what already exists." This latter factor is sometimes overlooked or not given enough emphasis in animal improvement investigations, but it is all important and probably the main reason why most adaptations are not absolutely perfect and why the selection applied by the domestic animal breeder for meat improvement cannot produce such rapid results as would be hoped.