Then consider the case of American immigration. Presumably alien welfare is less than American, but the would-be alien benefits tremendously from leaving his homeland. Assume also that Americans benefit from immigration (at least in small amounts) because they get cheap labour, etc. Under immigration both groups are better off, but if this increase is offset by increase in the population, then average welfare is lower. Thus although everyone is better off, this is not the preferred outcome. Parfit asserts that this is simply absurd. Parfit then discusses the identity of future generations. In Chapter 16 of "Reasons and Persons" he posits that one's existence is intimately related to the time and conditions of one's conception. Parfit calls this "The Time-Dependence Claim": "If any particular person had not been conceived when he was in fact conceived, it is in fact true that he would never have existed. Study of weather patterns and other physical phenomena in the 20th century has shown that very minor changes in conditions at time T have drastic effects at all times after T. Compare this to the romantic involvement of future childbearing partners. Any actions taken today, at time T, will affect who exists after only a few generations. For instance, a significant change in global environmental policy would shift the conditions of the conception process so much that after 300 years none of the same people that would have been born are in fact born. Different couples meet each other and conceive at different times, and so different people come into existence. This is known as the 'non-identity problem'. We could thus craft disastrous policies that would be worse for nobody, because none of the same people would exist under the different policies. If we consider the moral ramifications of potential policies in person-affecting terms, we will have no reason to prefer a sound policy over an unsound one provided that its effects are not felt for a few generations. This is the non-identity problem in its purest form: the identity of future generations is causally dependent, in a very sensitive way, on the actions of the present generations. Parfit met Janet Radcliffe Richards in 1982, and they then began a relationship that lasted until his death. They married in 2010. Richards believes Parfit had Asperger syndrome. Parfit supported effective altruism. He was a member of Giving What We Can and pledged to donate at least 10% of his income to effective charities. Parfit was an avid photographer who regularly traveled to Venice and St. Petersburg to photograph architecture.