Identity Argument
The identity argument states that a living creature is at all points in its development identical to the living creature that it was at an earlier point in time. In other words, over time a human being, for example, remains the same as what he or she was as an embryo. According to this argument, the dignity of a person cannot be added at a later point in time but must be recognised from the beginning of the individual's existence.
Different Positions can be found in:
Geach, P. (1962). Reference and Generality. Cornell.
Wiggins, D. (1967). Identity and Spatio-Temporal Continuity. Oxford.
Lee, P. (2004). The Pro-Life Argument from Substantial Identity: A Defence. In Bioethics 18(3), 249-263. http://doi.org/10.1111/j.1467-8519.2004.00393.x
Singer, P. (1980). Practical Ethics. Cambridge University Press.
Brock, D. W. (2006). Is a consensus possible on stem cell research? Moral and political obstacles. In Journal of Medical Ethics 32(1), 36-42. http://doi.org/10.1136/jme.2005.013581
Strong, C. (2006). Preembryo Personhood: An Assessment of the President’s Council Arguments. In Theoretical Medicine and Bioethics 27(5), 433-453. http://doi.org/10.1007/s11017-006-9016-7
Mauron, A. & Baertschi, B. (2004). The European Embryonic Stem-Cell Debate and the Difficulties of Embryological Kantianism. In Journal of Medicine and Philosophy: A Forum for Bioethics and Philosophy of Medicine 29(5), 563-581. http://doi.org/10.1080/03605310490514234