A spare or an individual? Cloning and the implications of monozygotic twinning.

The creation of Dolly, the cloned sheep, raises the scenario of cloning in humans. Neither the case for, nor against, the ethics of cloning in humans is discussed in this paper. Instead, it considers the neglected issue of the likely happiness or otherwise of the resulting children if they are born as monozygotic twins or triplets. The advantages and disadvantages of twinship are discussed in detail, and it is concluded that recognized medical risks, and incompletely understood psychological effects, should be given serious consideration.