26
The principle of bodily development, accounting for these common bodily ends, presupposes a
real human nature. This principle is no moot point; it carries grave moral significance. In Ten Universal
Principles: A Brief Philosophy of the Life Issues, Fr. Robert Spitzer explains the principle of full human
potential as a foundational principle for ethics. This principle was first refined by the Dominican friar
Bartolome de las Casas while defending Native Americans against Spanish slave traders. He argued that
“a people cannot be justifiably branded ‘less than human’ because of their degree of development if
they show the potential to achieve that development in the future.” 94 Fr. Robert Spitzer expresses the
heart of the principle as “[t]he potential to achieve full development is sufficient to establish the nature
of the being.” 95 Full development does not refer to a human being at one particular stage in life, rather
to what that human being will become when unhindered and free to grow as destined. While this
principle immediately appears as a pro-life principle better suited for the abortion controversy, the
appearance is deceiving. This principle invokes the importance of bodily development for deducing
personhood: the common morphology of the human body (leaving out aberrations as special cases) is a
criterion for characterizing a particular being as a human being.
In The Selfhood of the Human Person, John Crosby elaborates upon Spitzer’s principle of full
human development. He reflects upon the beginning of personal subjectivity and seeks to answer the
question of when human persons come into existence in their unique subjectivity as human persons.
Essentially, he argues that when the physical body begins at conception, so too the human person
begins, thus personhood begins even when the body is a single-celled zygote immediately following
fusion of egg and sperm. 96 He provides two smaller arguments to support his larger claim: first, from the
nature of the human person; and second, from the nature of the human fetus.
Is there anything in the nature of the human person that would prevent a zygote from being a
human person? If, it is possible to show that something in human personhood prevents a zygote from
being a human person, then the significance of the physical body needs to be reconsidered from
principles previously established. However, if not, then the functional concepts inherent to the physical
body – active even in fetal growth – maintain the significance ascribed to them by earlier principles.
John Crosby argues from the human person that people experience personhood even when dreamlessly
sleeping and in states of unconsciousness. As a common human experience, people assume a continuity
of self between their personal being before and after dreamless sleep. 97 This assumption rests upon the
94
Robert Spitzer, S.J., Ten Universal Principles: A Brief Philosophy of the Life Issues (San Francisco: Ignatius Press,
2011), 47.
95
Ibid, 48.
96
John Crosby, The Selfhood of the Human Person (Washington, D.C.: The Catholic University of America Press,
1996), 141.
97
John Crosby, The Selfhood of the Human Person (Washington, D.C.: The Catholic University of America Press,
1996), 141.