- The completion of the human genetic input is already complete at the single cell stage.
- Full differentiation is not complete until early adulthood.
- Both genetic and developmental individuality begin at fertilization.
- Any parallel between "brain death" and "brain birth" is scientifically invalid.
- The arguments used to define personhood are not grounded on scientific fact.
One area of stem cell research is controversial. Cells taken from early embryos are believed to hold more promise because of their greater potential for adapting into different types of tissue. (A problem is likely to be tissue rejection, which is not the case when the stem cells are taken from a person's own cells.)
Critics say that early embryos are small human beings - not just a "bunch of cells" to be harvested. The destruction of these embryos, they say, is unethical, unlike "adult" stem cells taken from umbilical cord blood and bone marrow.
A crucial factor in the debate is what the scientific evidence reveals.
The case that embryos are human persons
Human embryologists know that by the end of fertilisation, the 23 chromosomes of the sperm, and the 23 chromosomes of the ovum, have combined to produce a human being, possessing 46 chromosomes- the kind and number specific for the human species.
Many writers using scientific data as their starting points argue that 'personhood' appears at different biological marker events during the development and growth of the human embryo.
After the 23 chromosomes of the male sperm and the 23 chromosomes of the female ovum have combined to form the one-cell human zygote containing 46 chromosomes, clearly only half of those chromosomes come from the mother, and are thus not genetically the same as any of her tissues.
Immediately, specifically human enzymes and proteins are produced. The completion of the human genetic input is already complete at this single cell stage.
The zygote will not gain or lose any genetic information throughout all of human development. This genetic information contains virtually all of the instructions for differentiation, totipotency (i.e., he ability to develop into a new organism), and all the development stages.
Genes will be turned on and off to cause the production of molecular information which occurs in successive stages throughout development.
The scientific debate: "genetic individuality" v "personhood"
Before that point, there is a "non-person". Thus only a "pre-embryo" (i.e., a "pre-person") is present up to the 14th day, because, at the blastocyst stage, only the inner layer of cells of the embryoblast will become the later foetus or adult human being.
All of the cells from the outer trophoblast layer (i.e., the outermost layer of cells that attaches to the uterine wall) are discarded after birth. (as the placenta, umbilical cord, etc). After 14 days, they say, there is "developmental individuality" (i.e. a "person"), because the formation of the primitive streak prevents twinning from taking place, and because there is finally full differentiation.
However, scientifically, this is incorrect. Many of these cells, in fact, become part of the later fetus and adult gut, median umbilical ligament (which extends from the apex of the urinary bladder to the umbilicus), and its cells are also part of early human blood formation.
Full differentiation, in fact, is not complete until early adulthood. Scientifically, then, both genetic and developmental individuality begin at fertilization.
Therefore, it is because all human infants (newborn as well as foetal) do not actively exercise rational attributes or sentience that they are all not persons, according to Singer and his colleagues.
Quoting directly from a PBS interview with Singer:
"Well as I used the term 'person' -- a 'person' is a being who is capable of anticipating a future, having wants and desires for the future, which are cut off, thwarted, if that person is killed.
And I think that is generally a greater wrong than it is to kill a being who has no sense of existing over time. And that might be, for example, a chicken has no sense of existing over time. And that, I think, is one reason why it's normally worse to kill a human being than to kill a chicken.
But also, of course, newborn babies have no sense of their own existence over time. So, it's not equivalent. Killing a newborn baby -- whether able-bodied or not -- I think, is never equivalent to killing a being who wants to go on living."
Others argue for some sort of brain-related criteria - either "rational attributes" (self-consciousness, autonomy, loving, willing, relating with the world around one, etc.) or "sentience" (the ability to feel pain or pleasure).
If one defines a human person in terms of "rational attributes" only, one will eventually have to argue also for the moral permissibility of the infanticide of normal healthy human infants (as many bio-ethicists do), since full rationality, or full brain integration or sentience are not present until well after birth.
Neurological researcher D. Gareth Jones has succinctly put it, the parallelism between "brain death" and "brain birth" is scientifically invalid. "Brain death" is the gradual or rapid cessation of the functions of a brain.
"Brain birth" is the very gradual acquisition of the functions of a developing neural system. This developing neural system is not a brain. He questions, in fact, the entire assumption and asks what neurological reasons there might be for concluding that an incapacity for consciousness becomes a capacity for consciousness once this point is passed.
Jones continues that the alleged symmetry is not as strong as is sometimes assumed, and that it has yet to be provided with a firm biological base. (D. Gareth Jones, "Brain birth and personal identity," Journal of Medical Ethics 15:4, 1989, p. 178.)
Defining a "person's" value and status
These arguments for "personhood" - i.e. "individuality", "rational attributes" or "sentience" - are based, not on scientific fact but on philosophical grounds.
For example, the following list of adult human patients may genetically be human beings, but the are not human "persons": Alzheimer's and Parkinson's patients, the senile, persons with mental illness, the mentally retarded, drug addicts, alcoholics, the comatose, patients with multiple sclerosis, paraplegics, cripples, patients in persistent "vegetative" state, and many more...
This is the position taken by Singer and other bioethics writers. Singer argues that the higher primates, e.g., dogs, pigs, apes, monkeys, are persons—but that some human beings, e.g., even normal human infants, and disabled human adults, are not persons.
Philosopher/bioethicist R.G. Frey has also published that many of the adult human beings on the above list are not "persons," and suggests that they be substituted for the higher primates who are "persons" in purely destructive experimental research. (R.G. Frey, "The ethics of the search for benefits: Animal experimentation in medicine," in Raanan Gillon (ed.), Principles of Health Care Ethics (New York: John Wiley & Sons, 1994), pp. 1067-1075.)
Quality of care
The quality of medical care for some of the above "less than perfect patients" could be affected if physicians, nurses and other health-care workers perceive patients as somehow "less than full human persons."
This might include the small uncomplicated details, which require care and attention on a routine daily basis, as well as some of the more complicated medical treatments.
When conflicts arise concerning these patients, there is a danger that they will be seen by some of those in the mediation process as "non-persons" whose "quality of life" does not demand that they be given equal respect and equal medical treatment.
This in turn can lead to poor quality health care both on a routine and acute basis, and abuse in medical research.
(Adapted from a paper by Dianne Irving, M.A., Ph.D., Assistant Professor of Philosophy and Bioethics at De Sales University, U.S.A.)