The biology of bioethics: uses and abuses of the scientific data
Gonzalo Herranz, department of Humanities and Medical Ethics, University of Navarra, Spain.
VI Course of update of the Higher Institute of Religious Sciences: Sciences for the Contemporary World
Science and Technique in a Christian Perspective
Pamplona, August 28, 2009
gradeThis class is focused on theology students, which makes it notably different from another of the same name.
The abusive use of the scientific data
The futility of the monozygotic twinning argument
The argument of tetragametic chimeras
The extraembryonic fate of pre-embryonic cells
Greetings and thanks.
Participating in a course dedicated to dealing with Science and Technology in a Christian Perspective leads one to suspect that those of us present here are convinced that there is a profound harmony between Christian religion and natural science. We know that there is no contradiction in God: The same One who created the world is the One who reveals Himself to us in Jesus Christ. The Second Vatican Council said it clearly: "In all fields of knowledge, the authentically scientific research and in conformity with moral norms, will never really be contrary to faith, because profane realities and those of faith have their origin in the same God" (GS 36).
And yet, the environment seems saturated with the opposite idea. In many scientific journals, and not only in the general media, the Church is reproached for mercilessly rejecting the consolation and benefits linked to many applications of science: contraception and certain forms of abortion, assisted reproduction techniques, the promises of the research Genetics or embryonic stem cell projects. It is also reprimanded for not taking the lead in all that is new, for not wanting to know, for not accepting the data of current science.
What is the truth of it? That there are disagreements between the scientific establishment and the Church is evident. The establishment is guide for a bioethics of efficiency, of technological power, of the transhuman future. The Church, as it has said again in the Instruction Dignitas personae, on some questions of Bioethics, wants to fulfill its duty to give voice to those who have no voice, and to cry out in defense of the poor of the world and of those who are threatened, despised and oppressed in their human rights.
Let us consider the paradigmatic case of the human embryo, for no one is more threatened, despised and oppressed. In the bioethical documents subscribed to by the powerful (parliamentary commissions, national committees, international associations), as well as in the great journals and treaties on human assisted reproduction, we find a unanimous, consolidated version of the human embryo as an uncertain and precarious biological entity, so much so that it cannot be recognized as a holder of the rights and privileges proper to the human person. Obviously, this is in open contradiction with the Catholic vision that demands the maximum and identical respect for the human being from the moment he/she is conceived in fertilization until he/she dies a natural death.
The confrontation is so radical that an impartial spectator might think that the protagonists are speaking in two mutually unintelligible languages, science on one side, piety on the other. Science is on one side, piety on the other. Where is that harmony between science and faith? Is it reasonable to continue to aspire to it?
My answer is affirmative. But it requires not limiting oneself to being convinced in theory that between science and true religion there can be no contradiction. It is necessary to overcome the impasse by means of critical study and friendly discussion . To begin with, it would be necessary to put some order in the house of science.
The biological sciences need continuous revision, so as not to be buried under the immense amount of interests and prejudices that invade them. And also so as not to lose their bearings, since these sciences are not worthwhile without the financial aid of a strong ethic. If they were to navigate autonomously, they would go nowhere; like the sailor who is guided by the prow of his own boat, they would be condemned to turn around themselves. Just as the navigator needs a compass and a map, the biology of man needs ethics.
And, vice versa, a healthy bioethics needs a healthy biology. This is this afternoon's topic : the biology of bioethics Why does ethics need biology?
Because bioethics is a hybrid of ethics and biology, of moral Philosophy and biological science. Philosophers, theologians and those who call themselves bioethicists talk a lot about the ethics of bioethics, but little, and not very well, about the biology of bioethics. And yet, a good cultivator of bioethics would have to spend many hours to learn biology, in order to have a critically evaluated, personally assumed knowledge . Biology confers identity to bioethics, it is part of its essence: it is its bios, its life.
This is my message. It is not enough, then, to master the principles, rules and procedures of ethics. knowledge It is essential to have a serious, up-to-date knowledge of biology: of its theoretical foundations and its methods. It is necessary, above all, to learn and practice the official document of critically reading biology, especially that of those fields that most directly concern us. The cultivator of bioethics, whoever writes about bioethics, must be able to guarantee the quality of the biological data he introduces in his reflections. Only then will he be able to correctly pose and solve problems and cases, propose norms, formulate criteria. And only then will he be able to educate himself and teach others.
It is worth insisting on the idea that bioethics is a hybrid of biology and ethics. It is interdisciplinary. Consequently, bioethics is not easy. It is not easy to become a sort of two-faced Janus, or to assemble a competent and united team. Especially when it comes to serious matters, serious matters, it is not decent to shirk the responsibility of bringing together good ethics and good biology. Biologists and ethicists must work together. But there is a limit to the division of functions. It would not be acceptable for ethicists to say: let the biologists give us their version of the facts, and we will provide the ethics. It is not decorous for the ethicist to limit himself to "believing" biology with the faith of a charcoal burner. It would not be academic to accept at face value, without prudent inquiry, the objectivity of the biological data that one needs to handle in one's programs of study or in one's classes.
Among other reasons, because it should not be forgotten that the cultivators of biology are human beings, made of the moral fiber of the common man, capable of cardinal virtues and capital vices. Although, in theory, they all recognize that ethics should encompass the work and the ambitions of biologists and physicians, many of them consider ethics as a hindrance that slows down their research and hinders their triumph: they are convinced to the marrow of their bones that man's salvation will come from the hand of science, not from that of ethics or religion.
To conclude this section of my talk, I would like to emphasize two points.
The first: the idea that, in bioethics in the Catholic tradition, the in-depth study of the biological data is particularly important. Cardinal Ratzinger put it very simply: "I will never tire of repeating it: for the Church, the language of nature is also the language of morality". There can be no more expressive praise for natural science, whose typical function is to decipher as accurately as possible the language of creation in order to interpret it, with the help of reason, in the light of faith. We cannot forget that, in the Catholic tradition, grace does not destroy nature, but loves it, knows it, respects it and perfects it.
The second: which is somewhat autobiographical, is to indicate that what has been said so far is, at bottom, a self-criticism. I, like any son of a neighbor, neglected my critical duties, I let myself be guided, until not long ago, by the scientific establishment. I have realized that in bioethics a lot of work has been done with unreliable, even invalid, scientific data . I am persuaded that a good part, if not all, of the so-called "experts", of those who played a stellar role in the human reproductive revolution, put, I have no doubt with all their good will, their scientific prestige and social influence at the service of their own scientistic mentality. In their conflict of interests between scientific objectivity and their so-called sociobiological projects, they allowed the latter to prevail: and they did not hesitate, probably with the best of intentions, to favor a clever interpretation of the data, in order to orient the biomedical research towards their ideological convictions.
The abusive use of the scientific data
It was not very difficult for them. They dominated the levers of scientific policy. They enjoyed universal prestige. Echoing a centuries-old tradition (a physician, a professor at Louvain, had already said in 1625 that "theologians, in these matters, do nothing more than follow the opinion of physicians"), Christopher Tietze, the greatest promoter of contraception, at an international meeting on IUDs, held in New York in 1964, warned that "theologians and jurists will usually accept the dominant consensus of the biologists and physicians of the moment: they will believe what the scientists say as if it were a fact. If we can convince the doctors at agreement that gestation, and therefore life, begins with implantation, our brothers and sisters at the other Schools will listen to us".
It was as simple as that. They turned out to be prophetic words: as we well know, "official" science says, since then, that human life begins with implantation. And, curiously, the most enthusiastic followers of the idea are among the bioethicists, be they philosophers, theologians or jurists.
Let us take an example: we need not leave Spain. When the first legislation on assisted reproduction was passed here, our deputies -as stated in the long preamble of Law 35/1988- were committed to "adjusting their work to the biological truth of our times". In order to know this "truth", the congress created a Special Commission for the Study of Human "in vitro" Fertilization and Artificial Insemination. In due time, the Commission drafted the so-called report Palacios, which was C with applause by the plenary session of the Executive Council of the House in April 1986.
The report offered to the deputies the idea of the pre-embryo as supported by the data of science. He reasoned as follows: from the axiomatic equation human life = individualized human being it follows that individualization is determined by two properties: uniqueness (being unique and unrepeatable) and unity (being only one). But science teaches that the unity of the human being is contradicted in the case of chimeras (zygotic or postzygotic); and that uniqueness is refuted by the existence of monozygotic twins. Thus, both situations, monozygotic twins and chimeras, contradict the necessary unity and uniqueness required to be able to affirm without fissures the individuality of the human being, so it must be concluded that, after fertilization, there is a period of uncertainty Genetics, of pre-individual indeterminacy, which lasts about 14 days. Only then, from day 14 of fertilization, an embryo can no longer cease to be what it is.
The report Palacios concluded that "it was not unfounded to admit that during these first 14 days of development -pre-anidating or pre-implantation phase- the embryo is not individualized, because [...] 'we do not know if it will be one of two or two of one'". And they recommended authorizing "the positive manipulation of embryos in their first fourteen days of life, because, since it cannot be guaranteed that they are already individualized at this stage, the pre-embryos do not present themselves as the object of protection as human beings." The deputies accepted the idea of the pre-embryo and approved the "Palacios Law", since science maintained that the different phases of the human development are embryologically differentiable, which justified that the ethical evaluation and legal protection of the pre-embryos should be equally differentiable.
Today, 20 years later, the notion of pre-embryo is still present in our Laws: in the one on assisted reproduction, of 2006, and in the one on biomedical research , of 2007. There are no longer, as in 1988, scientific or ontological digressions in them. The BOE states that the concept of pre-embryo is "in line with the biological truth of our time".
And the same is true practically everywhere. With strange unanimity, the legislators of many countries have adopted the premises and conclusions expressed 30 years ago in 1979 by the American Ethics Advisory Board: that the human embryo in the first 14 days of its existence does not possess the biological attributes, nor does it enjoy the ethical dignity or the legal status of human beings properly speaking: it deserves an indeterminate measure of respect, but not the respect accorded to the human individual.
What reasons did biologists give to their brethren at the other Schools to support the notion of the pre-embryo?
Those contained in the report Palacios: that the human embryo during the 14 days of its existence can divide and thus originate two or more twins; that two pre-embryos can recombine and merge into a chimera. Another argument made a great impression: the one that affirmed that, in those 14 days, the internship totality of the cells of the conceptus are destined to construct extra-embryonic Structures , and as the extra-embryonic is not properly an embryo, the concepti are, and must be called, pre-embryos.
The time has truly come for the biology of bioethics.
What is the factual soundness of these arguments? What observations and experiments corroborate them?
These questions may seem like anachronistic questions. For many, the pre-embryo is a thing of the past. I think not.
After critically reading much, much bibliography, I can give those questions a twofold answer:
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That, indeed, these three statements (about monozygotic twins, about tetragametic chimeras, about cellular composition) are universally and peacefully accepted in the biomedical field.
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That they have no factual basis. They are examples, surprising in our incredulous 21st century, of what Francis Bacon called idola tribus: universally accepted prejudices, hasty generalizations, never subjected to rigorous scrutiny.
The second part of the answer may seem shocking, pretentious: so much so that some of you may begin to doubt my mental health, to think of me as a visionary, a victim of my own prejudices. I think, however, that I can show you that these are futile and empty arguments, mere exaggerations.
The futility of the monozygotic twinning argument
This argument states that, during its first 14 days, the human embryo is capable of splitting into two or more twins. Consequently, the pre-embryo does not have full human status, it has not yet reached its irrevocable individuality.
This bioethical argument has two arms. One, philosophical, which has caused rivers of ink to flow, revolves around the complex concepts of the individual and the person. I will not go into it. The other arm, biological, confronts us with the chronology of monozygotic twinning, which, it is claimed, extends to the first 14 days.
Biology is unanimous today: in the human species, the capacity to give rise to twins extends from the day after fertilization, when the zygote divides into the first two blastomeres, until the fourteenth day, when the primitive streak is formed. Once the primitive streak is formed, the ability to give rise to twins is extinguished.
But there is more. The different structure of the fetal envelopes reveals when the twin splitting took place. It is a classic calendar: when the cleavage occurs in the blastomeric segmentation phase, between days 2 and 3, dichorionic-diamniotic twins are born. When it occurs between days 4 and 8, monochorionic-diamniotic twins result. When, which rarely occurs, the cleavage takes place between days 9 and 13, monochorionic-monoamniotic twins are formed. Finally, the cleavage is even later, on or after day 14, is usually incomplete and results in the production of conjoined twins, the so-called Siamese twins.
But, do things happen like that? Does this description correspond to real, verified facts?
The answer is no: this description is a mere exercise of imagination. The cited calendar was imagined, as a hypothetical model , in 1922 by G. W. Corner. He introduced it, at the end, in a article in which he described porcine monochorionic twins. Corner presented it as a speculative exercise, as a mere suggestion that tried to correlate the structure of the fetal membranes (chorionicity, amnionicity) with certain moments of the embryonic development . Boldly, he extrapolated his thinking to the human species. Corner said: "I am going to indulge in a brief exercise of imagination on the morphogenesis of human monochorionic twins".
Curiously, Corner's intellectual "prank", ingenious and very rational, but merely imagined, became over the years solid orthodoxy. Corner's outline , including dichorionic monozygotic twins (in 1922, it was thought that dichorionics were without exception dizygotic) is today an official icon, an undisputed paradigm, and a dogma that has not generated heretics. Thirty-three years later, in 1955, Corner himself, somewhat astonished by the success of his hypothesis, said: "embryologists and obstetricians have drawn on paper the morphological theory of uniovular twinning, and we have imagined the different ways in which the zygote can develop two embryos in the end. All this, elaborated by conjecture, is already in all the manuals ..."
But, to this day, no one has corroborated the theory with evidence, which does not prevent it from continuing to enjoy almost total credibility. It is like geocentric astronomy before Copernicus. Very rarely, and only very recently, someone points out a criticism. And since at the origin of all research there is a question, a rebellion, since there is none here, there has been no research. The result is clear: as far as the chronology of twinning is concerned, we are at the starting line. That, in a world as innovative as biomedicine, a theoretical model has been neither corroborated nor refuted for more than eight decades is unheard of. Last June, Charles Boklage wrote: "We always talk about the relative timing of twinning: it is so easy to understand that it leaves us unmotivated to go on. But there has to be a molecular basis for that chronology: cells cannot read clocks or graphical schemes."
There is, however, an explanation for this. No one has ever observed, and probably never will be able to observe, live, how an embryo becomes two in the mother's body. But, one may ask, has no one observed the twinning of the embryo in vitro? Hundreds of thousands of human zygotes, morulae and blastocysts have been examined in vitro. However, so far, no reliable data, data has been provided on the chronology of twinning, and this is because, by mechanisms that have not yet been clarified, IVF causes an increase in monozygotic twinning. Many articles have been published on this phenomenon and its possible causes. Alterations of the pellucida, delayed implantation, central apoptosis or spontaneous excision of the inner cell mass, decreased intercellular adhesiveness due to a drop in the level of calcium in the blastocyst, disruption of intercellular communication, alterations of synchrony have been mentioned. Nothing has been proven. No progress has been made in clarifying the moment at which embryo cleavage occurs.
I am not exaggerating. We still have no real description of the mode and timing of human twinning. A button from sample. There appeared in Fertility & Sterility, September 2005, a poster graduate "Challenging traditional dogma: Two cases of late monozygotic division appearing as dichorionic twinning". I said to myself: it seems that, at last, someone is taking a crack at Corner's outline . I did not have time to send an e-mail to the authors. They replied that they had never followed these cases and were not going to publish them in detail.
Another: last December, Mio and Maeda published in Am J Obstet Gynecol slow-motion videos of the changes observed in human embryos cultured in vitro. They are spectacular. One of these videos shows two twin blastocysts: two inner cell masses had formed in each. But the video does not make clear how or when the twinning occurred. The Japanese authors make much of finding that the twinned blastocysts underwent repeated phases of collapse and re-expansion. But they do not know what relationship this phenomenon may have to twinning.
I am hopeful that Corner's venerable model will eventually be disallowed. Alternative models must be devised that take into account the spatial complexity of the embryo. In crystallography, a law states that, above a certain level of complexity, no crystal twinning is possible. It is logical to suspect that twin cleavage occurs at the first division of the zygote. We know that the embryo already from the beginning has poles and planes, is asymmetric; that the first blastomeres are not equivalent. This new image contrasts with that of the "amorphous" embryo, homogeneous, made of elements equal to each other and totipotent, which could separate into casual groups, capable at any moment of establishing each one of them two new and complete systems of bodily symmetry, two sets of axes in the three directions of space. And we also know that, in the embryo, molecular decisions are made long before their morphological effects are manifested.
In summary: the dominant model of twin chronology is a mere hypothesis, never demonstrated. On such a weak biological basis, it does not seem ethically justified to expropriate the dignity of human beings less than 14 days old. It is an inadmissible abuse.
The argument of tetragametic chimeras
This argument in favor of the pre-embryo idea is very apparent. It says that, during their first 14 days, two dizygotic embryos can amalgamate into a single embryo. If twinning made one embryo into two, chimerical fusion makes two embryos into one. The fact that these two embryos have different pairs of sex chromosomes leads to the training of hermaphrodite or genitally ambiguous individuals.
The argument insists on the already known idea: in the first two weeks, the individuality of the embryo is not ready, it remains in a fluid state. But, behind its spectacular appearance, the argument is very weak.
The information we have today on human chimeras is, in addition to being scarce, very complicated. Despite the refinements of the molecular Genetics , it is still very difficult to distinguish between certain types of genuine chimeras and some forms of genetic mosaicism.
Chimeras and mosaics are characterized as organisms in which mixed cell populations of different genotypes coexist. On paper, the definitions of mosaics and chimeras are precise: In mosaics, different cell lines originate from a single zygote, i.e., from a single individual: they are offspring of a single cell lineage, from which populations of different genotypes originate because of genetic or chromosomal errors produced after fertilization, such as gene mutations or mitotic disruptions
In contrast, a chimera Genetics is an organism in which cell populations from two or more individuals coexist. There is a B variety of chimeras. Many of them are minimal and are called microchimerisms. Microchimerism is very common. It occurs in women who have had pregnancies, as it is common for cells from the fetus to pass through the placenta and colonize the mother's organs. It occurs in subjects who have received blood transfusions or tissue or organ transplants. It occurs in monochorionic twins, in whose placentas the two circulations cross.
Also called chimeras, in a broad and improper sense, are very infrequent cases resulting from fertilization errors: they are the so-called parthenogenetic chimeras, chimeras due to simultaneous fertilization of the oocyte and the second polar corpuscle, and androgenetic chimeras. In these, diverse cell populations coexist, each with its own distinctive karyotype. From the diagnostic point of view, it can be very difficult to differentiate these chimeras, in the improper sense, from the chimeras in the strict sense, the chimeras by aggregation of two embryos.
As each of the embryos that amalgamate is result from the fertilization of an oocyte by a spermatozoon, genuine chimeras derive from four gametes; for this reason, they are called tetragametic chimeras. They are extraordinarily rare: although some 30 suspected cases have been published in the last fifty years, only five or six have been shown to possess the genetic markers required today to accept their tetragametic origin. This is a topic for which we have very little factual information.
But what interests us is not so much whether there are few or many tetragametic chimeras. The question that matters is: how long can the fusion of two embryos into one take place? In other words, does the ability to amalgamate last one day, a few days, all 14?
In no work on human tetragametic chimeras, original or revision, I have been able to find any allusion to their chronology, supposed or observed. No one knows. To claim that it can occur over 14 days is a gratuitous assertion. As an argument in favor of the pre-embryo, it lacks force, it is premature. We will have to wait to know how and when spontaneous tetragametic human chimeras originate.
The extraembryonic fate of pre-embryonic cells
This argument exerted an intense, one might almost say decisive, influence on the minds of non-scientists, especially politicians, to entrench the pre-embryo idea.
He states that, during the first two weeks, the human organism at development is made up of two cell populations: one, massively predominant, destined to form the fetal part of the placenta and the fetal membranes (chorion, amnion, allantois); the other, minuscule, the body of the embryo. The reality, we are told, is that in the pre-embryo there are hardly any cells that can properly be called embryonic cells. This enormous disproportion between the two cellular compartments (the extra-embryonic and the embryonic) in the organism in development of less than 14 days old forces us to speak of it as a pre-embryo, since it would not be correct to call an embryo what is not. The cells present in the first 14 days are destined to form Structures which will be discarded at the moment of delivery.
We see this from the very beginning of development: almost from the very beginning there are two cell populations: a small embryoblast and a dominant trophectoderm (TE). The former will give rise to the inner cell mass, from which the body of the embryo and some embryonic appendages will derive; the latter will form the trophoblast cells of the placenta.
In its Ethical Considerations of New Reproductive Technologies, the American Fertility Society's committee of Ethics concluded: "The initial events of the development are devoted to establishing extraembryonic tissues and functions, not embryonic tissues and functions [...] Therefore, the zygote, the morula, the young blastocyst cannot be considered as embryonic stages, but pre-embryonic [...] The term embryo is to be reserve for the outline of the future individual, which will only appear at the end of the second week after fertilization."
Formulated in this way, the argument seems persuasive, as it consists of two elements that enter through the eyes. One, the disparity in the numbers of the two cell populations. The other, the disparity in value, let's call it anthropological, between the body and the secondaries. Basically, the proponents of the argument want to tell us that using zygotes, morulae or blastocysts at research is equivalent, at internship, to destroying extraembryonic, disposable material.
And, in fact, it was very convincing. It was used to great effect by embryologist Anne McLaren in the days leading up to the vote on the Human Assisted Reproduction Bill in the British Parliament. McLaren used her prestige to convince parliamentarians. He told them: "At the end of 14 days we have a relatively large mass of tissue derived from the fertilized egg [...]. Almost all of that tissue-99% or 99.9‰-is extra-embryonic. The embryo itself is formed from a small issue of as yet uncommitted cells when the so-called primitive streak appears and forms the axis of the embryo."
Comes the inevitable question of the biology of bioethics: Does the argument have a real, scientifically proven basis? Is what McLaren said a scientific exhibition or a rhetorical dalliance? From entrance, it is surprising in a serious scientist that he can move his numbers by an order of magnitude, going from one cell in a hundred to one in a thousand is a laxity that is not compatible with science.
An aside is not out of place here: the promoter of the argument, Anne McLaren, had years earlier promoted the "Numerology" of development. This was the title of a article she had published in 1972. She had her disciples work on embryo cell counts. In 1976, at a symposium on Embryogenesis, he presented the results obtained in the mouse embryo from fertilization to birth. It is relatively easy during the first 4 or 5 days. After that, there is no choice but to make indirect estimates (in serial histological sections, or by dissecting the components and determining their weight and volume, or by studying the mitotic indices). Everything becomes very complex and difficult. The figures offered by McLaren indicate that the embryonic fate cells represent, on days 4 and 7.5, respectively 25 and 13% of the total cell population. They never fall below this level. From day 7.5 onwards there is no reliable numerical data .
The data concerning human embryos that have been published tell us that the human blastocyst has approximately 60, 160 and over 200 cells, on days 5, 6 and 7 respectively, and that of these approximately 40 percent correspond to the inner cell mass. We do not have data of what happens afterwards: obtaining them would require the removal of human embryos that initiate implantation. It is known that the trophoblast proliferates very aggressively when invading the endometrium, but the inner cell mass itself also increases very rapidly the issue of its cells to constitute the two cell sheets (epiblast and hypoblast) and contribute cells to the amniotic epithelium and the endoderm of the yolk sac. Whatever the case may be, we are far from McLaren's 1 per hundred or 1 per thousand.
I referred earlier that the argument of cell counts pretends to establish an anthropological distancing between the body of the embryo, on the one hand, and the placenta and fetal membranes, on the other. A sort of antagonism between one and the other. Nothing could be further from the truth: both tissues need each other. The inner cell mass financial aid maintains the proliferative capacity of the trophectoderm, and the trophectoderm supports the continued development of the inner cell mass. If they are separated from each other, embryonic stem cells can be cultured, but not an integrated embryo. There is no boundary between envelopes and embryo. Germ cells form in the yolk sac wall and migrate into the body of the embryo: without them there would be no propagation of the species. Blood cells originate in the extraembryonic position and then pass into the embryo. The vessels of the embryo start in the allantois, which connects the placental circulation with that of the embryo. More recent embryology is rehabilitating the basic role of the extraembryonic Structures , restoring them to the rank and function of embryonic organs.
In conclusion: the data offered by McLaren are to be taken as numerical metaphors, not as a quantitative representation of biological reality.
I close with a conclusion and a wish.
The conclusion is this: without a strong and critical biology there can be no sound bioethics. The partnership between biomedical scientists and bioethicists is essential. Because we have neglected it, we have suffered greatly.
The wish is that we strive to dismantle the pre-embryo theory. It is both an ethical error and a scientific error. In time, it will be forgotten. But first it must be rectified. Let us not forget that a large part of the work of science and ethics consists in rectifying errors.