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Ethical and Policy Developments 
reproduction. They argue that directed destruction of ex vivo 
embryos for the purpose of research would not result in greater 
embryonic loss than occurs in this natural process and would 
result in far greater benefits for humanity. The rate of natural 
embryo loss after conception in unassisted human reproduc- 
tion (taking in losses both before and after implantation), 
though not accurately known, is thought to be high, some 
suggest as high as 80 percent. Moreover, the fact of natural 
loss is now fairly well known, so that persons who engage in 
unprotected intercourse, whether seeking to reproduce or not, 
are knowingly bringing about the conception of many embryos 
that will die. We generally do not regard this embryo loss as 
unacceptably tragic, and we do not engage in great efforts to 
avert it or to find ways to diminish it (beyond research to pre- 
vent miscarriage, or instance). For this reason, these commen- 
tators argue, using artificially created embryos for purposes of 
research would not destroy a greater portion of those embryos 
than ordinarily die in natural unassisted reproduction. 
Moreover, they suggest, the high rate of natural embryo loss 
should call into question the views of those who believe that 
early-stage human embryos merit equal treatment with human 
children and adults. If so many die in the natural course of 
things, why do we not treat natural procreation as a great 
fountain of tragedy and carnage? The natural rate of embryo 
loss, and most people's failure to mourn its consequences, they 
suggest, should teach us something about the limited signifi- 
cance of human embryos in the earliest stages. One observer 
adds that the same logic should diminish our concerns about 
creating extra human embryos for research, as long as suffi- 
cient embryos are created for implantation to keep the chances 
of survival for any given embryo as good as the chances in 
natural reproduction. Another argues further that human 
embryonic stem cell research might actually raise the probabil- 
ity of longer survival for all humans, including embryonic ones, 
and is therefore a case of permissible taking of life, even on the 
assumption that the embryos are persons. 
Opponents of this view, however, have argued that natural 
deaths of embryos and the deaths caused by intentional efforts 
to destroy ex vivo embryos for research are not morally equiva- 
lent. There are many things that happen naturally that we are 
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