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All further stages and events in embryological develop- 
ment, they argue, are discrete labels applied to an organism 
that is persistently itself even as it continuously changes in its 
dimensions, scope, degree of differentiation, and so on. We can 
learn names for the various stages as if they were static and 
discrete, but the living and developing embryo is continuously 
dynamic.®^ More to the point, in the view of these commenta- 
tors no discrete point in time or development would seem to 
give any justification for assuming that the embryo in question 
was one thing at one point and then suddenly became some- 
thing different (turning, for example, from non-human to hu- 
man or from non-person to person). None of the biological 
events (or “points" in processes), they contend, is sufficient to 
tell us what we are morally permitted or obligated to do to 
human embryos, in the absence of one or another additional 
premises that shape one’s view of these biological events. And 
if one’s guiding premise is that all human persons possess 
equal moral standing — ^regardless of their particular powers, 
size, or appearance — ^then there are no grounds for denying 
the earliest human embryo full moral standing as a person. 
Some critics of this position argue that it makes too much of 
mere genetic identity and (uncertain) potential or that it does 
not make enough of present condition and the significance of 
development itself.®® ’There is more to being human, some ob- 
servers argue, than possessing a human genome or spontane- 
ous cell division, and it matters that the early human embryo is 
but a ball of cells, without sentience or sensation and without 
human form.®^ It matters, too, they argue, that an ex vivo hu- 
man embryo does not have the potential to develop independ- 
ently, without further technical intervention.®® Indeed, some 
argue that a human embryo in its earliest stages is essentially 
no different from any human tissue culture in the laboratory,®® 
or that, because the ex vivo embryo cannot develop if left to 
itself, it cannot be thought of as truly continuous with more 
developed human organisms. It may be, in the description of 
one observer, not much different from a pile of building materi- 
als stored in a warehouse.®’ 
Nonetheless, advocates of the argument from continuity 
suggest that it is dangerous to begin to assign moral worth on 
the basis of the presence or absence of particular capacities 
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