## 1. The Ethics of Destroying Human Embryos for Research




The potential therapeutic benefits of HESC research provide strong
grounds in favor of the research. If looked at from a strictly
consequentialist perspective, it's almost certainly the case that
the potential health benefits from the research outweigh the loss of
embryos involved and whatever suffering results from that loss for
persons who want to protect embryos. However, most of those who
oppose the research argue that the constraints against killing innocent
persons to promote social utility apply to human embryos. Thus,
as long as we accept non-consequentialist constraints on killing
persons, those supporting HESC research must respond to the claim that
those constraints apply to human embryos.




In its most basic form, the central argument supporting the claim
that it is unethical to destroy human embryos goes as follows: It
is morally impermissible to intentionally kill innocent human beings;
the human embryo is an innocent human being; therefore it is morally
impermissible to intentionally kill the human embryo. It is worth
noting that this argument, if sound, would not suffice to show that all
or even most HESC research is impermissible, since most investigators
engaged in HESC research do not participate in the derivation of HESCs
but instead use cell lines that researchers who performed the
derivation have made available. To show that researchers who use
but do not derive HESCs participate in an immoral activity, one would
further need to establish their complicity in the destruction of
embryos. We will consider this issue in section 2. But for
the moment, let us address the argument that it is unethical to destroy
human embryos.


### 1.1 When does a human being begin to exist?




A premise of the argument against killing embryos is that human
embryos are human beings. The issue of when a human being begins
to exist is, however, a contested one. The standard view of those
who oppose HESC research is that a human being begins to exist with the
emergence of the one-cell zygote at fertilization. At this stage,
human embryos are said to be "whole living member[s] of the
species homo sapiens ... [which] possess the epigenetic primordia
for self-directed growth into adulthood, with their determinateness and
identity fully intact" (George & Gomez-Lobo 2002,
258). This view is sometimes challenged on the grounds that
monozygotic twinning is possible until around days 14-15 of an
embryo's development (Smith & Brogaard 2003). An
individual who is an identical twin cannot be numerically identical to
the one-cell zygote, since both twins bear the same relationship to the
zygote, and numerical identity must satisfy transitivity. That
is, if the zygote, A, divides into two genetically identical cell
groups that give rise to identical twins B and C, B and C cannot be the
same individual as A because they are not numerically identical with
each other. This shows that not all persons can correctly assert
that they began their life as a zygote. However, it does not
follow that the zygote is not a human being, or that it has not
individuated. This would follow only if one held that a condition of an
entity's status as an individual human being is that it be
impossible for it to cease to exist by dividing into two or more
entities. But this seems implausible. Consider cases in
which we imagine adult humans undergoing fission (for example, along
the lines of Parfit's thought experiments, where each half of the
brain is implanted into a different body) (Parfit 1984). The
prospect of our going out of existence through fission does not pose a
threat to our current status as distinct human persons. Likewise,
one might argue, the fact that a zygote may divide does not create
problems for the view that the zygote is a distinct human being.




There are, however, other grounds on which some have sought to
reject that the early human embryo is a human being. According to
one view, the cells that comprise the early embryo are a bundle of
homogeneous cells that exist in the same membrane but do not form a
human organism because the cells do not function in a coordinated way
to regulate and preserve a single life (Smith & Brogaard 2003,
McMahan 2002). While each of the cells is alive, they only become
parts of a human organism when there is substantial cell
differentiation and coordination, which occurs around day-16 after
fertilization. Thus, on this account, disaggregating the cells of
the 5-day embryo to derive HESCs does not entail the destruction of a
human being.




This account is subject to dispute on empirical grounds. That there is
some intercellular coordination in the zygote is revealed by the fact
that the development of the early embryo requires that some cells
become part of the trophoblast while others become part of the inner
cell mass. Without some coordination between the cells, there would be
nothing to prevent all cells from differentiating in the same
direction (Damschen, Gomez-Lobo and Schonecker 2006). The question
remains, though, whether this degree of cellular interaction is
sufficient to render the early human embryo a human being. Just how
much intercellular coordination must exist for a group of cells to
constitute a human organism cannot be resolved by scientific facts
about the embryo, but is instead an open metaphysical question
(McMahan 2007a).


### 1.2 The moral status of human embryos




Suppose that the 5-day human embryo is a human being. On the
standard argument against HESC research, membership in the species
*Homo sapiens* confers on the embryo a right not to be
killed. This view is grounded in the assumption that human beings
have the same moral status (at least with respect to possessing this
right) at all stages of their lives.




Some accept that the human embryo is a human being but argue that
the human embryo does not have the moral status requisite for a right
to life. There is reason to think that species membership is not
the property that determines a being's moral status. We
have all been presented with the relevant thought experiments, courtesy
of Disney, Orwell, Kafka, and countless science fiction works. The
results seem clear: we regard mice, pigs, insects, aliens, and so on,
as having the moral status of persons in those possible worlds in which
they exhibit the psychological and cognitive traits that we normally
associate with mature human beings. This suggests that it is some
higher-order mental capacity (or capacities) that grounds the right to
life. While there is no consensus about the capacities that
are necessary for the right to life, some of the capacities that have
been proposed include reasoning, self-awareness, and agency (Kuhse
& Singer 1992, Tooley 1983, Warren 1973).




The main difficulty for those who appeal to such mental capacities
as the touchstone for the right to life is that early human infants
lack these capacities, and do so to a greater degree than many of the
nonhuman animals that most deem it acceptable to kill (Marquis
2002). This presents a challenge for those who hold that the
non-consequentialist constraints on killing human children and adults
apply to early human infants. Some reject that these constraints apply
to infants, and allow that there may be circumstances where it is
permissible to sacrifice infants for the greater good (McMahan
2007b). Others argue that, while infants do not have the
intrinsic properties that ground a right to life, we should nonetheless
treat them as if they have a right to life in order to promote love and
concern towards them, as these attitudes have good consequences for the
persons they will become (Benn 1973, Strong 1997).




Some claim that we can reconcile the ascription of a right to life to
all humans with the view that higher order mental capacities ground
the right to life by distinguishing between two senses of mental
capacities: "immediately exercisable" capacities and
"basic natural" capacities. (George and Gomez-Lobo 2002,
260). According to this view, an individual's immediately exercisable
capacity for higher mental functions is the actualization of natural
capacities for higher mental functions that exist at the embryonic
stage of life. Human embryos have a "rational nature," but
that nature is not fully realized until individuals are able to
exercise their capacity to reason. The difference between these types
of capacity is said to be a difference between degrees of development
along a continuum. There is merely a quantitative difference between
the mental capacities of embryos, fetuses, infants, children, and
adults (as well as among infants, children, and adults). And this
difference, so the argument runs, cannot justify treating some of
these individuals with moral respect while denying it to others.




Given that a human embryo cannot reason at all, the claim that it
has a rational nature has struck some as tantamount to asserting that
it has the potential to become an individual that can engage in
reasoning (Sagan & Singer 2007). But an entity's
having this potential does not logically entail that it has the same
status as beings that have realized some or all of their potential
(Feinberg 1986). Moreover, with the advent of cloning
technologies, the range of entities that we can now identify as
potential persons arguably creates problems for those who place great
moral weight on the embryo's potential. A single somatic
cell or HESC can in principle (though not yet in practice) develop into
a mature human being under the right conditions--that is, where
the cell's nucleus is transferred into an enucleated egg, the new
egg is electrically stimulated to create an embryo, and the embryo is
transferred to a woman's uterus and brought to term. If the
basis for protecting embryos is that they have the potential to become
reasoning beings, then, some argue, we have reason to ascribe a high
moral status to the trillions of cells that share this potential and to
assist as many of these cells as we reasonably can to realize their
potential (Sagan & Singer 2007, Savulescu 1999).
Because this is a stance that we can expect nearly everyone to reject,
it's not clear that opponents of HESC research can effectively
ground their position in the human embryo's potential.




One response to this line of argument has been to claim that embryos
possess a kind of potential that somatic cells and HESCs lack. An
embryo has potential in the sense of having an "active
disposition" and "intrinsic power" to develop into a
mature human being (Lee & George 2006). An embryo can
mature on its own in the absence of interference with its development.
A somatic cell, on the other hand, does not have the inherent capacity
or disposition to grow into a mature human being. However, some
question whether this distinction is viable, especially in the HESC
research context. While it is true that somatic cells can realize
their potential only with the assistance of outside interventions, an
embryo's development also requires that numerous conditions
external to it are satisfied. In the case of embryos that are
naturally conceived, they must implant, receive nourishment, and avoid
exposure to dangerous substances *in utero*. In the case
of spare embryos created through in vitro fertilization--which
are presently the source of HESCs for research--the embryos must
be thawed and transferred to a willing woman's
uterus. Given the role that external factors--including 
technological interventions--play in an embryo's
realizing its potential, one can question whether there is a morally
relevant distinction between an embryo's and somatic cell's
potential and thus raise doubts about potentiality as a foundation for
the right to life (Devolder & Harris 2007).




Some grant that human embryos lack the properties essential to a
right to life, but hold that they possess an intrinsic value that calls
for a measure of respect and places at least some moral constraints on
their use: "The life of a single human organism commands
respect and protection ... no matter in what form or shape,
because of the complex creative investment it represents and because of
our wonder at the divine or evolutionary processes that produce new
lives from old ones." (Dworkin l992, 84). There are,
however, divergent views about the level of respect embryos command and
what limits exist on their use. Some opponents of HESC research
hold that the treatment of human embryos as mere research tools always
fails to manifest proper respect for them. Other opponents take a
less absolutist view. Some, for example, deem embryos less
valuable than more mature human beings but argue that the benefits of
HESC research are too speculative to warrant the destruction of
embryos, and that the benefits might, in any case, be achieved through
the use of noncontroversial sources of stem cells (e.g., adult stem
cells) (Holm 2003).




Many, if not most, who support the use of human embryos for HESC
research would likely agree with opponents of the research that there
are some circumstances where the use of human embryos would display a
lack of appropriate respect for human life, for example, were they to
be offered for consumption to contestants in a reality TV competition
or destroyed for the production of cosmetics. But proponents of the
research hold that the value of human embryos is not great enough to
constrain the pursuit of research that may yield significant
therapeutic benefits. Supporters of the research also frequently
question whether most opponents of the research are consistent in their
ascription of a high value to human embryos, as opponents generally
display little concern about the fact that many embryos created for
fertility treatment are discarded.


### 1.3 The case of "doomed embryos"




When spare embryos exist after fertility treatment, the individuals
for whom the embryos were created typically have the option of storing
for them for future reproductive use, donating them to other infertile
couples, donating them to research, or discarding them. Some
argue that as long as the decision to donate embryos for research is
made after the decision to discard them, it is morally permissible to
use them in HESC research even if we assume that they have the moral
status of persons. The claim takes two different forms. One is
that it is morally permissible to kill an individual who is about to be
killed by someone else where killing that individual will help others
(Curzer, H. 2004). The other is that researchers who derive HESCs
from embryos that were slated for destruction do not cause their
death. Instead, the decision to discard the embryos causes their
death; research just causes the manner of their death (Green 
2002).




Both versions of the argument presume that the decision to discard
spare embryos prior to the decision to donate them to research entails
that donated embryos are doomed to destruction when researchers receive
them. There are two arguments one might marshal against this
presumption. First, one who wants to donate embryos to research
might first elect to discard them only because doing so is a
precondition for donating them. There could be cases in which one
who chooses the discard option would have donated the embryos to other
couples were the research donation option not available. The fact
that a decision to discard embryos is made prior to the decision to
donate the embryos thus does not establish that the embryos were doomed
to destruction before the decision to donate them to research was
made. Second, a researcher who receives embryos could choose to
rescue them, whether by continuing to store them or by donating them to
infertile couples. While this would violate the law, the fact
that it is within a researcher's power to prevent the destruction
of the embryos he or she receives poses problems for the claim that the
decision to discard the embryos dooms them or causes their
destruction.


## 2. The Ethics of Using Human Embryonic Stem Cells in Research




Assume for the sake of argument that it is morally impermissible to
destroy human embryos. It does not follow that all research with HESCs
is impermissible, as it is sometimes permissible to benefit from moral
wrongs. For example, there is nothing objectionable about
transplant surgeons and patients benefiting from the organs of murder
and drunken driving victims (Robertson 1988). If there are
conditions under which a researcher may use HESCs without being
complicit in the destruction of embryos, then those who oppose the
destruction of embryos could support research with HESCs under certain
circumstances.




Researchers using HESCs are clearly implicated in the destruction of
embryos where they derive the cells themselves or enlist others to
derive the cells. However, most investigators who conduct
research with HESCs obtain them from an existing pool of cell lines and
play no role in their derivation. One view is that we cannot assign
causal or moral responsibility to investigators for the destruction of
embryos from which the HESCs they use are derived where their
"research plans had no effect on whether the original immoral
derivation occurred." (Robertson 1999). This view
requires qualification. There may be cases in which HESCs are
derived for the express purpose of making them widely available to HESC
investigators. In such instances, it may be that no individual
researcher's plans motivated the derivation of the cells.
Nonetheless, one might argue that investigators who use these cells are
complicit in the destruction of the embryos from which the cells were
derived because they are participants in a research enterprise that
creates a demand for HESCs. For these investigators to avoid the charge
of complicity in the destruction of embryos, it must be the case that
the researchers who derived the HESCs would have performed the
derivation in the absence of external demand for the cells (Siegel
2004).




The issue about complicity goes beyond the question of an HESC
researcher's role in the destruction of the particular human
embryo(s) from which the cells he or she uses are derived. There
is a further concern that research with existing HESCs will result in
the future destruction of embryos: "[I]f this research
leads to possible treatments, private investment in such efforts will
increase greatly and the demand for many thousands of cell lines with
different genetic profiles will be difficult to resist." (U.S.
Conference of Catholic Bishops 2001). This objection faces two
difficulties. First, it appears to be too sweeping:
research with adult stem cells and non-human animal stem cells, as well
as general research in genetics, embryology, and cell biology could be
implicated, since all of this research might advance our understanding
of HESCs and result in increased demand for them. Yet, no one,
including those who oppose HESC research, argues that we should not
support these areas of research. Second, the claim about future
demand for HESCs is speculative. Indeed, current HESC research
could ultimately reduce or eliminate demand for the cells by providing
insights into cell biology that enable the use of alternative sources
of cells (Siegel 2004). 




While it might thus be possible for a researcher to use HESCs
without being morally responsible for the destruction of human embryos,
that does not end the inquiry into complicity. Some argue that
agents can be complicit in wrongful acts for which they are not morally
responsible. One such form of complicity arises from an
association with wrongdoing that symbolizes acquiescence in the
wrongdoing (Burtchaell 1989). The failure to take
appropriate measures to distance oneself from moral wrongs may give
rise to "metaphysical guilt," which produces a moral taint
and for which shame is the appropriate response (May 1992).
The following question thus arises: Assuming it is morally
wrongful to destroy human embryos, are HESC researchers who are not
morally responsible for the destruction of embryos complicit in the
sense of symbolically aligning themselves with a wrongful act?




One response is that a researcher who benefits from the destruction
of embryos need not sanction the act any more than the transplant
surgeon who uses the organs of a murder or drunken driving victim
sanctions the homicidal act (Curzer 2004). But this response
is unlikely to be satisfactory to opponents of HESC research.
There is arguably an important difference between the transplant case
and HESC research insofar as the moral wrong associated with the latter
(a) systematically devalues a particular class of human beings and (b)
is largely socially accepted and legally permitted. Opponents of HESC
research might suggest that the HESC research case is more analogous to
the following kind of case: Imagine a society in which the
practice of killing members of a particular racial or ethnic group is
legally permitted and generally accepted. Suppose that biological
materials obtained from these individuals subsequent to their deaths
are made available for research uses. Could researchers use these
materials while appropriately distancing themselves from the wrongful
practice? Arguably, they could not. There is a heightened
need to protest moral wrongs where those wrongs are socially and
legally accepted. Attempts to benefit from the moral wrong in these
circumstances may be incompatible with mounting a proper protest
(Siegel 2003).




But even if we assume that HESC researchers cannot avoid the taint
of metaphysical guilt, it is not clear that researchers who bear no
moral responsibility for the destruction of embryos are morally
obligated not to use HESCs. One might argue that there is a prima
facie duty to avoid moral taint, but that this duty may be overridden
for the sake of a noble cause.


## 3. The Ethics of Creating Embryos for Stem Cell Research and Therapy




Most HESCs are derived from embryos that were created for infertility
treatment but that were in excess of what the infertile individual(s)
ultimately needed to achieve a pregnancy. The HESCs derived from these
leftover embryos offer investigators a powerful tool for understanding
the mechanisms controlling cell differentiation. However, there are
scientific and therapeutic reasons not to rely entirely on leftover
embryos. From a research standpoint, creating embryos through cloning
technologies with cells that are known to have particular genetic
mutations would allow researchers to study the underpinnings of
genetic diseases *in vitro*. From a therapeutic standpoint, the
HESCs obtained from leftover IVF embryos are not genetically diverse
enough to address the problem of immune rejection by recipients of
stem cell transplants. (Induced pluripotent stem cells may ultimately
prove sufficient for these research and therapeutic ends, since the
cells can (a) be selected for specific genetic mutations and (b)
provide an exact genetic match for stem cell recipients.) At present,
the best way to address the therapeutic problem is through the
creation of a public stem cell bank that represents a genetically
diverse pool of stem cell lines (Faden *et al*. 2003, Lott &
Savulescu 2007). This kind of stem cell bank would require the
creation of embryos from gamete donors who share the same HLA-types
(i.e., similar versions of the genes that mediate immune recognition
and rejection).




Each of these enterprises has its own set of ethical issues. In the
case of research cloning, some raise concerns, for example, that the
perfection of cloning techniques for research purposes will enable the
pursuit of reproductive cloning, and that efforts to obtain the
thousands of eggs required for the production of cloned embryos will
result in the exploitation of women who provide the eggs (President's
Council on Bioethics 2002, Norsigian 2005). With respect to stem cell
banks, it is not practically possible to create a bank of HESCs that
will provide a close immunological match for all recipients. This
gives rise to the challenge of determining who will have biological
access to stem cell therapies. We might construct the bank so that it
provides matches for the greatest number of people in the population,
gives everyone an equal chance of finding a match, or ensures that all
ancestral/ethnic groups are fairly represented in the bank (Faden
*et al*. 2003, Bok, Schill, & Faden 2004, Greene 2006).




There are, however, more general challenges to the creation of embryos
for research and therapeutic purposes. Some argue that the creation of
embryos for non-reproductive ends is morally problematic, regardless
of whether they are created through cloning or in vitro
fertilization. There are two related arguments that have been advanced
to morally distinguish the creation of embryos for reproductive
purposes from the creation of embryos for research and therapeutic
purposes. First, each embryo created for procreative purposes is
originally viewed as a potential child in the sense that each is a
candidate for implantation and development into a mature human. In
contrast, embryos created for research or therapies are viewed as mere
tools from the outset (Annas, Caplan & Elias 1996, President's
Council on Bioethics 2002). Second, while embryos created for research
and therapy are produced with the intent to destroy them, the
destruction of embryos created for reproduction is a foreseeable but
unintended consequence of their creation (FitzPatrick 2003).




One response to the first argument has been to suggest that we
could, under certain conditions, view all research embryos as potential
children in the relevant sense. If all research embryos were
included in a lottery in which some of them were donated to individuals
for reproductive purposes, all research embryos would have a chance at
developing into mature humans (Devander 2005). Since
those who oppose creating embryos for research would likely maintain
their opposition in the research embryo lottery case, it is arguably
irrelevant whether embryos are viewed as potential children when they
are created. Of course, research embryos in the lottery case would be
viewed as both potential children and potential research tools.
But this is also true in the case of embryos created for reproductive
purposes where patients are open to donating spare embryos to
research.




As to the second argument, the distinction between intending and
merely foreseeing harms is one to which many people attach moral
significance, and it is central to the Doctrine of Double Effect.
But even if one holds that this is a morally significant distinction,
it is not clear that it is felicitous to characterize the destruction
of spare embryos as an unintended but foreseeable side-effect of
creating embryos for fertility treatment. Fertility clinics do
not merely foresee that some embryos will be destroyed, as they choose
to offer patients the option of discarding embryos and carry out the
disposal of embryos when patients request it. Patients who elect
that their embryos be discarded also do not merely foresee the
embryos' destruction; their election of that option manifests
their intention that the embryos be destroyed. There is thus
reason to doubt that there is a moral distinction between creating
embryos for research and creating them for reproductive purposes, at
least given current fertility clinic practices.


##  4. Stem Cell-Derived Gametes




Recent scientific work suggests it is possible to derive gametes from human pluripotent stem cells. Researchers have generated sperm and eggs from mouse ESCs and iPSCs and have used these stem cell-derived gametes to produce offspring (Hayashi 2011; Hayashi 2012).
While it may take several years before researchers succeed in deriving gametes from human stem cells, the research holds much promise for basic science and clinical application. For example, the research could provide important insights into the fundamental processes of gamete biology, assist in the understanding of genetic disorders, and provide otherwise infertile individuals a means of creating genetically related children. The ability to derive gametes from human stem cells could also reduce or eliminate the need for egg donors and thus help overcome concerns about exploitation of donors and the risks involved in egg retrieval. Nonetheless, the research gives rise to some controversial issues related to embryos, genetics, and assisted reproductive technologies (D. Mathews *et al*. 2009).




One issue arises from the fact that some research on stem cell-derived
gametes requires the creation of embryos, regardless of whether one is
using ESCs or iPSCs. To establish that a particular technique for
deriving human gametes from stem cells produces functional sperm and
eggs, it is necessary to demonstrate that the cells can produce an
embryo. This entails the creation of embryos through in vitro
fertilization. Since it would not be safe to implant embryos created
during the early stages of the research, the likely disposition of the
embryos is that they would be destroyed. In such instances, the
research would implicate all of the moral issues surrounding the
creation and destruction of embryos for research. However, the
creation of embryos for research in this situation would not
necessitate the destruction of the embryos, as it does when embryos
are created to derive stem cell lines. One could in principle store
them indefinitely rather than destroy them. This would still leave 
one subject to the objection that life is being created for
instrumental purposes. But the force of the objection is questionable
since it is not clear that this instrumental use is any more
objectionable than the routine and widely accepted practice of
creating excess IVF embryos in the reproductive context to increase
the probability of generating a sufficient number of viable ones to
produce a pregnancy. 


 Further issues emerge with the prospect of being able to produce
large quantities of eggs from stem cells. As the capacity to identify
disease and non-disease related alleles through preimplantation
genetic diagnosis (PGD) expands, the ability to create large numbers
of embryos would substantially increase the chances of finding an
embryo that possesses most or all of the traits one wishes to select.
This would be beneficial in preventing the birth of children with
genetic diseases. But matters would become morally contentious if it
were possible to select for non-disease characteristics, such as
sexual orientation, height, superior intelligence, memory, and musical
ability. One common argument against using PGD in this way is that it
could devalue the lives of those who do not exhibit the chosen
characteristics. Another concern is that employing PGD to select for
non-disease traits would fail to acknowledge the "giftedness of
life" by treating children as "objects of our design or
products of our will or instruments of our ambition" rather
accepting them as they are given to us (Sandel 2004, 56). There is
additionally a concern about advances in genetics heightening
inequalities where certain traits confer social and economic
advantages and only the well-off have the resources to access the
technology (Buchanan 1995). Of course, one can question whether the
selection of non-disease traits would in fact lead to devaluing other
characteristics, whether it would alter the nature of parental love,
or whether it is distinct enough from currently permitted methods of
gaining social and economic advantage to justify regulating the
practice. Nonetheless, the capacity to produce human stem
cell-derived gametes would make these issues more pressing. 


## 5. Stem Cell-Derived Organoids, Gastruloids, and Synthetic Embryos




There have been a number of recent scientific studies in which stem
cells have, under certain *in vitro* culture conditions,
self-organized into three-dimensional structures that resemble and
recapitulate some of the functions of human organs (Lancaster &
Knoblich 2014; Clevers 2016). These "organoids" have been
established with human stem cells for a variety of organs, including,
among others, the kidney, liver, gut, pancreas, retina, and brain. In
addition to organoids, stem cells have been shown to self-organize
into embryo-like structures *in vitro*. Human embryonic stem
cells have formed structures - referred to as
"gastruloids" - that bear some resemblance to
embryos during gastrulation, which is the stage several days after
implantation where the body plan and some tissues tissue types,
including the central nervous system, start to develop (Warmflash et
al. 2014; Deglincerti *et al*. 2016; Shahbazi 2016). Researchers have
also combined mouse embryonic stem cells and trophoblast stem cells to
create "synthetic embryos," which have a structure akin to
pre-implantation embryos (Rivron *et al*. 2018). Synthetic embryos have
been shown to implant into the mouse uterus, though their potential to
develop to term has not been demonstrated.



While these scientific advances offer promising avenues for better
understanding human development and disease, they also raise some
novel and challenging ethical issues. In the case of organoids,
cerebral organoids raise the most vexing issues. Researchers have
produced cerebral organoids with a degree of development similar to
that of a few-months-old embryo, and have already used them to study
how the Zika virus causes microcephaly in fetuses (Garcez *et al*.
2016). At present, there is some evidence that cerebral organoids may
be able to receive afferent stimulations that produce simple
sensations (Quadrato *et al*. 2017). However, they currently lack the
kind of mature neural networks and sensory inputs and outputs
essential to the development of cognition. If, through bioengineering,
human cerebral organoids were to develop the capacity for cognition,
that would provide grounds for ascribing an elevated moral status to
them, and it would raise concomitant issues about our moral
obligations towards them. In the nearer term, it is more likely that
cerebral organoids will develop some degree of consciousness Assuming
we have a shared understanding of consciousness (e.g., phenomenal
consciousness), one challenge is to identify means of measuring the
presence of consciousness, since a cerebral organoid cannot
communicate its internal states (Lavazza & Massimini 2018). But
even if we can verify that an organoid is conscious, there remains the
question of the moral significance of consciousness (Shepherd
2018). There is debate over whether consciousness has intrinsic value
(Lee 2018), and whether in some cases it is better for a conscious
being to not possess it (Kahane & Savulescu 2009). Those who
reject the intrinsic value and moral significance of consciousness
might find the case of a conscious entity that has led a solely
disembodied existence, emerges and persists in the absence of any
social or cultural nexus, and lacks beliefs and desires, to be a
paradigmatic case where the value of consciousness is doubtful.


 With respect to gastruloids and synthetic embryos (if the latter
are successfully produced with human stem cells), the central question
is whether these entities are sufficiently like human embryos in their
structure and functions to give rise to moral concerns about their use
in research. Gastruloids do not possess all the characteristics of an
embryo, as they do not form all of the embryonic tissues (e.g., they
do not have the trophectoderm, which mediates the attachment to the
uterus). At the same time, gastruloids may, with extra-embryonic
tissues, achieve a developmental stage in which they manifest a whole
body plan. Recall that one argument (discussed in Section 1.1 above)
for rejecting that human embryos are human beings is that the cells
that comprise the early embryo do not function in a coordinated way to
regulate and preserve a single organism. Gastruloids can in principle
operate with this higher level of coordination. While one may still
reject that this characteristic of gastruloids confers human rights on
them, their more advanced stage of development might ground reasonable
claims for according them greater respect than embryos at an earlier
stage. In the case of both gastruloids and human synthetic embryos,
the possibility that they ultimately lack the potential to develop
into mature human beings may be of significance in morally
distinguishing them from normal human embryos. As noted previously (in
section 1.2 above), one argument for ascribing a high moral status to
human embryos and for distinguishing the potential of human embryos
from the potential of somatic cells and embryonic stem cells is that
embryos have an "active disposition" and "intrinsic
power" to develop into mature humans on their own. If synthetic
embryos and gastruloids do not possess this disposition and power,
then those who oppose some forms of human embryo research might not
object to the creation and use of human gastruloids and synthetic
embryos for research.