  There are, however, other grounds on which some have sought to reject that the early human embryo is a human being. According to one view, the cells that comprise the early embryo are a bundle of homogeneous cells that exist in the same membrane but do not form a human organism because the cells do not function in a coordinated way to regulate and preserve a single life (Smith &amp; Brogaard 2003, McMahan 2002). While each of the cells is alive, they only become parts of a human organism when there is substantial cell differentiation and coordination, which occurs around day-16 after fertilization. Thus, on this account, disaggregating the cells of the 5-day embryo to derive HESCs does not entail the destruction of a human being.