And on the fourteenth day ... potential and identity in embryological development.

Australian legislation at both state and federal levels has been passed in the last two years enabling the creation and use of cloned embryos up until their fourteenth day of development. Yet for this fourteen-day threshold to carry moral weight it must be shown that an embryo may be plausibly attributed some kind of moral standing after this point that it cannot be accorded before it. Moral standing may be conferred using Steven Buckle's account of potential to become (after one problem with his account is dealt with) but such standing has often been withheld from the embryo prior to the fourteenth day due to the possibility of monozygotic twinning and the violation of numerical continuity this represents. This article discusses the influential argument regarding monozygotic twinning articulated by Peter Singer and Helga Kuhse, and finds it insufficient to negate either the 'identity thesis' they describe or Buckle's account of potential to become.