  The assertion that all persons have equal basic moral worth and dignity calls out for justification or at least elucidation. What is it about persons that renders them all morally equal in some fundamental sense? One proposal is that a being becomes morally considerable by gaining some capacity for rational agency, for thinking through what ought to be done and setting one's will to do it, and that if one attains rational agency capacity at a certain threshold level, one becomes a full person, and further increases in rational agency above that threshold line that some might attain would not affect one's fundamental status of being a person with the same worth and dignity possessed by all other persons (Nozick 1974, chapter 3).