Recently, a new attempt was put to the United Nations to ban all human cloning, including therapeutic or research cloning. The advocates of this ban mainly based their position on the conviction that the human embryo has the same moral status as a person and should be treated with equal respect. But should the status of embryos or embryo-like entities that are generated by new technologies, such as somatic-cell nuclear transfer (SCNT), be considered with the same theories and principles as the status of embryos that are created by in vitro fertilization? These technologies raise a number of fundamentally new questions about the nature and moral status of embryos.

First, there is a classification problem: which entities should be classed as human embryos1? Traditional criteria, which include fertilization by human gametes, have to be abandoned as a necessary condition, because SCNT embryos are produced without fertilization. According to some, any cell from which a human being could, in principle, be created — even if assisted by sophisticated technology — should be regarded as a human embryo. However, this 'inclusive' definition implies that all somatic cells of a person's body have to be considered as (equivalent to) embryos — an untenable view. The urgency of the classification problem is highlighted by the production of hybrids through the transfer of a human somatic nucleus into an enucleated animal ooplast2. Some proponents argue that embryos created in this way are non-human because their mitochondrial DNA is non-human. Another criterium for a human embryo is that it has the potential to become a person, but this is challenged by the production of human parthenotes, which are created by the artificial activation of unfertilized eggs. Parthenotes cannot develop into full organisms and therefore do not fulfil the condition of potentiality.

Second, if these 'high-tech constructs' are considered to be human embryos, what about their moral status? In particular, the evidence indicates that embryos that are obtained by SCNT have a strongly reduced viability — what are the ethical implications of this? If this evidence is corroborated, research cloning would no longer be merely distinguished from reproductive cloning by the intention of the scientist. It might even be possible to design the SCNT technology to guarantee that, from the start, the embryo or embryo-like entity completely lacks the capacity to develop into a human being, like parthenotes. In this case, one of the main arguments in favour of respecting the human embryo — its potential to become a human being — would no longer be valid for embryos that are created by SCNT or parthenogenesis. This would also apply to certain categories of embryos that are created in the context of medically assisted reproduction3. With these points in mind, it is not obvious that all entities that are classified as embryos deserve the same respect.

As new techniques are being developed, we urgently need clarification of both the definition of the human embryo and the moral status of human embryos with limited viability. These questions need to be addressed in a continuing dialogue between scientists, ethicists and policymakers worldwide.