Sam Harris abuses human embryology

Sam Harris is one of the “New Atheists.” He is the author of several books, but “Letter to a Christian Nation” is the one I would like to discuss in this post.

Harris takes conservative Christians to task for opposing embryonic stem cell research. While doing this he implies that Christians are horribly ignorant about human embryology, and their beliefs are not consonant with the facts of human embryology and logic.

On page 29 of his book, Harris writes, “A three-day-old human embryo is a collection of 150 cells called a blastocyst.” Problems begin immediately for Harris. In the first place a three-day-old human embryo does not consist of 150 cells and it is not yet a blastocyst. After the completion of fertilization, the zygote divides 22-26 hours later and becomes a two-cell-stage embryo. The second cleavage occurs about 12-14 hours later, but this is not a synchronous division, since three-cell stage embryos are commonly observed. The third cleavage occurs 18-24 hours later, which takes us into the second day of life for the embryo, and this heralds the start of the morula stage of the embryo. The fourth and fifth cleavages produce the 16- and 32-cell-stage embryos, and these are observed roughly three days after fertilization. The embryo has not yet formed a hollow sphere of cells, and will require another day or so to do that. Therefore right in the beginning, Harris shows his ignorance of human embryology while he is dressing down Christians for being ignorant.

Harris continues by noting that the number of cells in the early embryo is about the same as those in the common house fly. Once again, Harris’ ignorance is on prominent display. The larval stage of the fruit fly, Drosophila melanogaster, contains 50,000 cells in one of its imaginal wing disc, which will form the wing and notum in the adult fly. The fly has two wings, and therefore, the wing discs of the larval fruit fly have 100,000 cells, which is far more than the early human embryo.

Harris continues by noting that early human embryos can split to form monozygotic twins, or fuse to form chimerical embryos. Harris chides Christians by stating, “No doubt theologians are struggling even now to determine what becomes of the extra human soul in such a case” (30). Harris shows that he has not read Christian literature on this subject. Plenty of people have thought about these issues, and they still disagree with Harris.

Twinning and chimerism are very rare events. Monozygotic twins account for about one in 350 live births (~0.3-0.4%; see Judith G. Hall, “Twinning,” Lancet 362 (2003): 735-43). This illustrates the largest problem with the twinning argument: Only a small proportion of human embryos show the ability to twin. Can we use such a rare event to make a blanket statement about the non-human status of all human embryos? One in 150 children has autism, but it would be completely illegitimate to take the symptoms of autism and argue that this is the way young children in general act. Such a conclusion is not valid for either autism or twinning.

There are additional concerns. First, monozygotic twinning runs in families and there seems to be a strong genetic component to it (Geoffrey Machin, “Familial Monozygotic Twinning: A Report of Seven Pedigrees,” American Journal of Medical Genetics Part C: Seminars in Medical Genetics 151C, no. 2 (2009): 152-4). In fact, since twinning is genetically determined, then it is entirely possible that twins are genetically determined, and therefore, the two beings that emerge as twins are in actuality two from conception, although in a latent form. This interpretation is certainly reasonable and it means that terminating these embryos would end two human lives and not just one.

Twinning rates also increase when the embryo is physically manipulated outside the mother’s body. Babies conceived through in vitro fertilization show two-to-five times the rates of monozygotic twinning (see Robert Geoffrey, Liselotte Mettler, and D. E. Walters, “Identical Twins and In Vitro Fertilization,” Journal of In Vitro Fertilization and Embryo Transfer 3 (1986): 114-7; Scott E. Sills, Michael J. Tucker, and Gianpiero D. Palermo, “Assisted Reproductive Technologies and Monozygous Twins: Implications for Future Study and Clinical Practice,” Twin Research 4 (2000): 217-23; Kenneth I. Aston, C. Matthew Peterson, and Douglas T. Carrell, “Monozygotic Twinning Associated with Assisted Reproductive Technologies: A Review,” Reproduction 136 (2008): 377-86). In this case, twinning is a response to slight injuries. The embryo responds by repairing the damage and in doing so, makes a second individual, without the benefit of sexual reproduction. Therefore, the ability of the embryo to form a twin does not indicate the absence of a human individual, but the remarkable ability of an organism to heal and restore those bits of itself that were damaged or lost.

Harris also used embryo fusion to argue against the personhood of human embryos. Two early human embryos can sometimes fuse to form one embryo composed of a mixture of two types of cells with distinct genetic fingerprints. This phenomenon is referred to as “chimerism,” and there are approximately thirty confirmed cases of it. Does chimerism mean that human embryos are not human persons? What would we do if teenagers were able to fuse to form one individual? We would not regard such teenagers as non-persons until they lose this ability. Then to be consistent, neither we nor Harris should regard the embryo as a non-person either just because a stark minority of them has the ability to fuse. Harris writes, “You or someone you know may have developed in this way.” His swagger makes it seem as though this is an exceedingly routine process, but it is not. Do we really want to condemn the majority of embryos that do not show this capacity as non-human persons?

What happened to the embryos that fused? They died and a new individual rose from their ashes. Given the rarity of chimerism, the embryo does not possess an active capacity to fuse, but undergoes fusion under rare conditions as a result of its ability to repair itself. If it is invalid to impute the ability to twin to all embryos, then it is surely unreasonable to impute an even rarer event like chimerism to all embryos.

An episode of Star Trek: Voyager, entitled “Tuvix” provides an excellent perspective on this question. In this episode, two members of the Voyager crew, Tuvok and Neelix, return to the ship by transporter, only to have the malfunctioning device merge the two individuals into one new person named “Tuvix.” While the crew eventually accepts Tuvix, others devise a way to separate the two individuals to their original states. However, Tuvix does not wish to die. Both Neelix and Tuvok were individuals before this event and Tuvix is also a person. The fusion of the two crew members did not affect their personhood before fusion occurred, and it does not affect the personhood of human embryos either.

Harris then calls the opposition to embryonic stem cell research “morally indefensible.” This is due to our objection that destroying early human embryos is tantamount to killing a human person. However, there is a further problem for Harris. Earlier in his book on page 12, Harris, after decrying the “obscene celebrations of violence that we find throughout the Old and New Testaments” (page 11), heaps one encomium after another on Jainism, a religion that originated in ancient India that surpasses the morality of Christianity because they believe in “Do not injure, abuse, oppress, enslave, insult, torment, torture, or kill any creature or living being” (page 23). But wait a minute! If the Jains are so morally upright, then why are we Christians so nasty because we want to champion to rights of a young human person? Even if the embryo is not a human person, would not Jainism agree with us? Wouldn’t the Christian then be worthy of as much praise from Harris as he just heaped upon Jainism? Devout Jains will sweep the ground in front of them to prevent their steps from killing insects, and their commitment to non-violence even extends to mosquitoes that carry malaria. Then why not praise evangelicals for taking a small step toward universal respect for all life? If Jains would oppose the destruction of a young human life, then why are Jains not condemned for the same reason?

On page 32, Harris calls opposition to embryonic stem cells research “uninformed.” We have seen that he is the ignorant one. He takes rare events in human development and generalizes them to all embryos, and then vastly overstates the significance of these rare events.  Instead these events show the early human embryo to be a unified, self-healing, and self-regulating entity much like other organisms.  In this regard the early human embryo is a human person, albeit a very young one.

Finally, if there is no God, then why should we care about the “little one with burns over 75% of her body?” She is simply an evolved mammal. She has no intrinsic value – why should we care? Harris’ book is silent about why we should, but thick on protests that we should. Harris has to steal from Christian ethics to make his arguments even though he denies the very foundations of them. In short, Harris’ book was not just unconvincing, but insulting, and strewn with logical and factual errors.

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Professor of Biochemistry at Spring Arbor University (SAU) in Spring Arbor, MI. Have been at SAU since 1999. Author of The Stem Cell Epistles. Before that I was a postdoctoral research fellow at the University of Pennsylvania in Philadelphia, PA (1997-1999), and Sussex University, Falmer, UK (1994-1997). I studied Cell and Developmental Biology at UC Irvine (PhD 1994), and Microbiology at UC Davis (MA 1986, BS 1984).