Foot's book "Natural Goodness" attempts a different line. The question that we have most reason to do ties into the good working of practical reason. This in turn is tied to the idea of the species of an animal providing a measure of good and bad in the operations of its parts and faculties. Just as one has to know what kind of animal is meant, for instance to decide whether its eyesight is good or bad, the question of whether a subject's practical reason is well developed depends on the kind of animal it is. This idea is developed in the light of a concept of animal kinds or species as implicitly containing "evaluative" content, which may be criticized on contemporary biological grounds. However, it is arguable even on that basis that it is deeply entrenched in human cognition. In this case, what makes for a well-constituted practical reason depends on us being human beings marked by certain possibilities of emotion and desire, a certain anatomy, neurological organization, and so forth.