Journal of Applied Philosophy, Vol. 25, No. 3, 2008 © Society for Applied Philosophy, 2008, Blackwell Publishing, 9600 Garsington Road, Oxford, OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA. Blackwell Publishing Ltd Oxford, UK JAPP Journal of Applied Philosophy 0264-3758 1468-5930 © Society for Applied Philosophy, 2008 > XXX Original Articles Life Extension versus Replacement Gustaf Arrhenius Life Extension versus Replacement GUSTAF ARRHENIUS  It seems to be a widespread opinion that increasing the length of existing happy lives is better than creating new happy lives although the total welfare is the same in both cases, and that it may be better even when the total welfare is lower in the outcome with extended lives. I shall discuss two interesting suggestions that seem to support this idea, or so it has been argued. Firstly, the idea there is a positive level of well-being above which a life has to reach to have positive contributive value to a population, so-called Critical Level Utilitarianism. Secondly, the view that it makes an outcome worse if people are worse off than they otherwise could have been, a view I call Comparativism. I shall show that although these theories do capture some of our intuitions about the value of longevity, they contradict others, and they have a number of counterintuitive implications in other cases that we ultimately have to reject them. Introduction It seems to be a widespread opinion that increasing the length of existing happy lives is better than creating new happy lives although the total welfare is the same in both cases, and that it may be better even when the total welfare is lower in the outcome with extended lives. I shall discuss two interesting suggestions that seem to support this idea. Firstly, the idea there is a positive level of well-being above which a life has to reach to have positive contributive value to a population. This view is usually called Critical Level Utilitarianism. Secondly, the view that it makes an outcome worse if people are worse off than they otherwise could have been. I shall call this view Comparativism. Firstly, I shall describe what I call the pure case of life extension versus replacement. Then I shall very briefly describe some different views about the value of life extension and indicate why I think some of the arguments in favour and against life extension fail. I shall then turn to the implications of Critical Level Utilitarianism and Comparativism in regards to life extension and replacement, which is the main topic of this paper. Life Extension versus Replacement: The Pure Case Consider the figure below (Figure 1). The figure below shows two outcomes (or populations as I shall sometimes say): A and B. The width of each block represents the number of people, and the height represents their lifetime welfare. These outcomes could consist of all the lives that are causally affected by, or consequences of a certain action or series of actions (a policy). All the lives in the above figure have positive welfare, or, as we also could put it, have lives worth living. 1