A comprehensive theory which relates tissue mechanical stresses to many features of skeletal morphogenesis, growth, regeneration, maintenance and degeneration is reviewed. The theory considers the repeated or intermittent mechanical forces which constitute the loading history on the chondro-osseous skeleton. The results of numerous mechanical stress analyses indicate that the local tissue stress history plays a major role in controlling connective tissue biology. The strong influence of mechanical energy in ontogenesis implies a comparably strong influence in phylogenesis. The fact that the mechanical stress histories in skeletal tissues are directly related to the force of gravity suggests that the life forms that have evolved on Earth are closely tied to our gravitational field.