The Asymmetry, also known as 'the Procreation Asymmetry,' is the idea in population ethics that there is a moral or evaluative asymmetry between bringing into existence individuals with good or bad lives. It was first discussed by Jan Narveson in 1967, and Jeff McMahan coined the term 'the Asymmetry' 1981. McMahan formulates the Asymmetry as follows: “while the fact that a person's life would be worse than no life at all ... constitutes a strong moral reason for not bringing him into existence, the fact that a person's life would be worth living provides no (or only a relatively weak) moral reason for bringing him into existence.” Professor Nils Holtug formulates the Asymmetry evaluatively in terms of the value of outcomes instead of in terms of moral reasons. Holtug's formulation says that “while it detracts from the value of an outcome to add individuals whose lives are of overall negative value, it does not increase the value of an outcome to add individuals whose lives are of overall positive value.”
Much of the literature on the ethics of procreation deals with the Asymmetry. A number of authors have defended the Asymmetry, and a number of authors have argued against it.