[Reflections on the beginning of a new human individual]

Although there is very little doubt that when a child is born a new actual person can be identified, there is continuous debate as to the moment in embryological development when that same person begins its existence. Based on today's knowledge of human fertilization and the early stages of embryo development, this position paper examines three theses that deal with the establishment of personhood. The first thesis stipulates that a human individual exists prior to syngamy. Although the sperm has penetrated the plasmatic membrane of the oocyte, the genetic information contained in both gametes remain separated in the male and female pronucleus; thus, the oocyte contains the sum of two identities responsible for creating a new individual. This paper will argue that a human individual has not yet formed. The second thesis recognizes that with syngamy, a unicellular structure (zygote) is established, endowed with genetic individuality and with the potential to become a person maintaining that same genetic framework throughout its lifetime. The third thesis argues that although genetic individuality is established with syngamy, the ontological individuality is only reached once genetic expression and cellular specialization are achieved and twinning is no longer possible (15 days after fertilization).