I have attempted to derive some of the assumptions that are implicit in the book. This may motivate Roberts to present more explicit statements. This enterprise provides us with a wealth of information, but there is no discussion of why animals stand up, or of how orientation might be related to the purposes of posture. While this is a real postural goal, it is not the only one that shapes postural control. This assumption, once made explicit, can easily be questioned.
Behavioral goals are of great importance for postural control.
The disinclination to discuss the function of postural control reflects a general absence in the book of issues relating to evolution, such as the adaptive aspects of behavior. Roberts does not define these terms, but it is hard to imagine any definition that does not refer to supra-postural goals. This begs the question of what is being recognized. The treatment of physics is detailed and accurate, but incomplete. Missing is any discussion of the dynamics of balance.