Appendices - Killing Happy Animals: Explorations in Utilitarian Ethics - page 147

Appendices
A. Different-number choices
As we have seen, Prior Existence Utilitarianism can successfully deal with
standard non-identity cases. Standard non-identity cases are presented
as same-number choices: in both outcomes, the same number of beings
exists. So, for instance, the 14-year-old girl will have one child. The
question is only when she will have it, and the timing affects the genetic
identity of the child. Different-number choices present a further chal-
lenge for the prior existence view.
In different-number choices, a different number of beings exist in each
outcome. So, for instance, the timing of the conception might deter-
mine not only the welfare level and genetic identity of the woman's
next child, but it determines also whether she will have twins or a
single child. Decisions that affect the identity and welfare of possible
beings may also affect their number. For instance, policy choices that
we make now might affect the welfare level of the future generation and
also the identities of those who will live. If this is the case, these policy
choices are also very likely to affect the size of the future generation and
thus the number of people that will live. Therefore, this kind of policy
choice seems to show the prevalence and relevance of different-number
choices. However, this kind of policy choice does not present us with
genuine non-identity cases. As has been argued, the same people may
exist in both outcomes, so it is not necessarily the case that they would
not otherwise have existed. 1 Furthermore, as Parfit says, this kind of
policy choice can better be construed as a same-number choice because
it is unclear what the impact is on the number of beings that will live. 2
So, let me make up a better example of a different-number choice. We
can slightly change the case of the 14-year-old girl and assume that the
girl is on a medication now that would cause her to have twins if she
conceived now. In a couple of years, she would not need this medication
anymore. So if she conceived later, she would have only one child. So,
the choice would be between one happy child later and two less happy
children now. Here is another, similar, case:
In vitro fertilisation: A woman is having an in vitro fertilisation
and she has to choose whether to implant one or rather two of the
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