Considering Embryos

As I wrote in a post over in another blog, a new book by Francis S. Collins, The Language of God: A Scientist Presents Evidence for Belief, nicely reconciles Darwinism with faith. Collins is the physician-geneticist who headed the Human Genome Project, and a committed evangelical Christian to boot, who believes in a God that cares about us and wants to be in fellowship with us. Collins also believes unreservedly in Darwinian evolution. The main point of his book is that the latter can be rather easily reconciled with the former.

Once Collins has made that argument (which I won't go into now) in the course of the book per se, he attaches a lengthy appendix dealing with issues of bioethics from a religious-scientific point of view. Among these issues are abortion, cloning, and research into human stem cells, some of which come from human embryos.

One of the topics he addresses in his discussion of the abortion issue is that of when precisely a feritilized egg cell which begins to divide and form an embryo takes on the status of a human life. From a religious perspective, this transition is usually identified with coming to possess a God-given soul.

Many religious people who oppose abortion outright say that it is at the moment of conception, at the instant when sperm meets egg, that the soul commences to be. From that point on, the embryonic life is fully human. To destroy the embryo on purpose is tantamount to murder. This indeed is, to the best of my understanding, the precise position of my own religious denomination, the Roman Catholic Church.

Collins points out a difficulty with this approach to the issue, though, one which I had never considered before. It is the case of identical twins.

Identical twins arise from a single fertilized egg, also known as a zygote. In the womb of the mother, the zygote begins to divide in the usual way, making an embryo of first two cells, then four, then eight, etc. But now something unusual happens: the embryo itself splits in two. It might be, in a given instance, an embryo of eight cells that turns into two separate embryos of four cells apiece. Those two embryos are just alike; they have the exact same DNA.

The two identical embryos then go on to increase in size, independently one one another, in the usual way. This happens by virtue of further cell divisions. At some point, the cells in each embryo begin to differentiate from one another, so as to form different tissues and organs. (The embryonic stem cells which now come into being play a crucial role in cell differentiation.) The two identical embryos soon become fetuses, and nine months or so after the single sperm from a father met the single egg from a mother, two healthy identical-twin babies are born.

As Collins points out, there was only one moment of conception, but the result has been two human infants, just alike in their DNA, but presumably with two independent souls. If the human soul "arrives" at the moment of conception, then in the identical-twins scenario, when and how does the second soul "arrive" — the one for the "extra" body that belongs to the "second" twin?


A second topic which Collins takes up involves, in its own way, a similar conundrum. In his discussion of stem-cell research, Collins points out a possible way around the ethical problem of obtaining embryonic stem cells only by destryoing embryos.

In the normal course of events, a human embryo in its mother's womb develops in the first four or five days of pregnancy into a blastocyst, a ball of 50-150 cells whose outer layer will form the enclosing placenta and whose inner cells, which consist of the embryonic stem cells or ESCs, will become a fetus. See "Embryonic stem cell" and related articles in Wikipedia for more on the science of embryonic stem cells.

The ESCs are "pluripotent," meaning that they can "develop into each of the more than 200 cell types of the adult body when given sufficient and necessary stimulation for a specific cell type." Adult bodies also make stem cells, but adult stem cells (ASCs) are only "unipotent." Each can generate only one type of organ or tissue.

Pluripotent ESCs accordingly have greater potential, if harvested and manipulated to be used in new therapies for diseases like Alzheimer's, in which cells in victims' bodies have died and need replacement.

The lines of embryonic stem cells currently used in ESC research all originated with embryos produced in fertility clinics. These were "excess" embryos that turned out not to be used in in-vitro fertilization procedures. They would otherwise be discarded. Some of them have been used instead to derive lines of embryonic stem cells, a process which has the side effect of destroying the embryos.

Collins notes that this sort of thing is ethically problematical from the point of view of those who believe the fertilized egg and resulting embryo already has a soul. So he suggests an alternative way to obtain embryonic human stem cells, a derivative of the procedure used in making clones such as Dolly the sheep.


The technique is called "somatic cell nuclear transfer" (SCNT). SCNT involves, as I understand it, removing the nucleus of an egg cell and replacing it with the nucleus of (say) a skin cell from a different donor.

The nucleus of an egg cell contains all the DNA that would normally be contributed by a mother to the eventual zygote that results when her egg is fertilized by a sperm cell from a father. The sperm which fertilizes the egg contains, in its own nucleus, the father's DNA. Each gamete, whether sperm or egg, contains half the number of chromosomes of an ordinary body cell. When sperm and egg meet and unify, a single nucleus results having the full complement of chromosomes.

When an unfertilized egg has its nucleus removed by a scientist and replaced with the nucleus of an ordinary body cell from a male or female donor other than the female that has produced the egg, the resulting cell (given the proper manipulation) is able to start dividing into an embryo. This embryo is in most ways just like an embryo that comes from the customary fertilization of an egg by a sperm ... except, of course, that the embryo will turn into a genetic clone of the donor of the nucleus. It will have no DNA whatsoever from the surrogate mother whose egg cell has been borrowed, and possibly in whose womb the embryo is implanted to be carried to term.

This is a brief summary of the process called somatic cell nuclear transfer or SCNT. Given that "somatic" means "bodily," or "of the body," you can see why the term is used. The nucleus (with its DNA) taken from a cell in the body of a donor organism is transferred to an egg cell from another (necessarily female) organism. The SCNT-derived cell then may develop into a clone of the nucleus donor.

Or, as Collins points out, the embryo which results from SCNT might be used to harvest embryonic stem cells. Instead of implanting it in a womb to be carried to term and given birth to, it can stay in a test tube until its stem cells are harvested; then the remainder of the blastocyst could be discarded. The stem cells thus harvested could well be as valuable to medical research as those which derive from a fertilized egg — because in most ways, the two sources of embryonic stem cells are just alike.

The question is, would an SCNT-derived blastocyst, intended to be used as a source of human stem cells, possess a soul? After all, if those who say the soul appears at the instant of conception are right, then in the case where there is nuclear transfer, but no sperm-egg conception, when and how would the soul appear?


This question is admittedly a tricky one. Presumably, an SCNT-derived human blastocyst could instead be introduced into a woman's womb, where it would actually turn into a baby who is a clone of the donor of the original nucleus. This has not actually been tried in humans, of course, as it has in sheep and other species. There are obvious religious and ethical objections, not to mention the practical and scientific problems of cloned organisms in other species not turning out as robust as might be hoped.

But let us say the practical problems could be solved and the ethical problems ignored. Would the clone-child have a soul? Most of us who believe in souls at all would answer an emphatic yes. After all, the process which turns a single fertilized egg into two identical twins in a mother's womb is a natural form of cloning. Admittedly, it is different in technical detail, but it results in two humans having identical DNA, even though there has been but one single fertilization of an egg by a sperm.


I have just given two cases in which it doesn't make sense to say the human soul "arrives" at the time of conception, when one sperm meets one egg, and only then. Of course, one might respond that God could make a "special delivery" of an "extra" soul when the embryo divides into twins, and that there is likewise a special delivery of a soul from God when a human embryo is derived via SCNT. But this sort of fixing up of the soul-arrival scenario isn't very intuitively satisfying, at least not to me.

And so I now question the whole idea of the soul "arriving." I have a completely different notion of what theologians call "ensoulment." I'll discuss it in a follow-up post, Of the Self and the Soul.