The biology of bioethics: uses and abuses of the scientific data
Gonzalo Herranz, department de Humanities and Medical Ethics, University of Navarra
conference closing lecture of Master's Degree of Bioethics: Temas core topic of Contemporary Bioethics
Catholic University of Murcia, January 22, 2009.
gradeThe content of this lecture is different from that of another of the same degree scroll pronounced in 2010 at the closing ceremony of the Master's Degree in Bioethics of the University of Navarra.
Uses and abuses of the data scientific
The fictitious biology of the pre-embryo
The futility of the monozygotic twinning argument
The futility of the argument of tetragametic chimeras
The futility of the argument of the extraembryonic destiny of the preembryo
I am happy to speak to people who are so convinced that biomedical science needs ethics that they have devoted many hours and efforts to study bioethics. They now reach Degree at Master's Degree. And if, from this moment on, they continue to study with commitment, this will become, in a certain way, part of their identity. Their card of presentation will be able to say with justice: So-and-so, Master in Bioethics.
He will be a person convinced that, without ethics, the biological sciences and their cultivators tend to lose their way, because what happens to them is what happens to a sailor who is guided by the bow of his own boat, which goes nowhere. He needs the financial aid of the compass or the probe, the profile of the coastline or the light of the lighthouse. A Master's Degree in bioethics knows that his first task is to bring ethics to laboratory or to the hospital, so that those who make and apply biomedical sciences guide their work in the respect for life and the dignity of the human being. They will not then lose their north.
This morning I am not going to address the ethics of bioethics. As expressed in the first words of the degree scroll I proposed for this intervention, I would like to deal with the biology of bioethics, with what biomedical science contributes to bioethics.
Bioethics is vitally interested in biology. In a way, biology confers identity and character to bioethics, it is part of its name and its essence. This means that it is not enough for the bioethicist to master with skill and professionalism the principles, rules and procedures of moral Philosophy . knowledge To be a bioethicist requires a serious, well-considered and up-to-date knowledge of biology: of its theoretical foundations, its methods of observation and experimentation. It also requires the ability to read critically the biological bibliography . The bioethicist must possess biological knowledge commensurate with his or her philosophical knowledge.
To be more specific: the competent cultivation of bioethics requires having learned, and continuing to learn throughout one's life, what is relevant in biomedicine; it requires skill to search, select and evaluate for oneself the biological data of the issues and problems that concern one. It is a task that each one has to assume with responsibility staff, guaranteeing the truth, reliability and quality of the biological data that he/she introduces in his/her reflections. Only in this way will the bioethicist be able to correctly resolve problems and cases, and will be able to formulate reliable norms and criteria.
It should not be forgotten that bioethics, at its very core, is interdisciplinary. It is born and grows from symbiosis, from the integration of ethics and the life and health sciences, from the dialogue they maintain with each other, from the questions they ask each other and the answers they give each other. Such interdisciplinarity has a stimulating consequence: bioethics is not easy, especially when it deals with serious matters. Because, at subject serious, it is not possible to resort to the division of functions. It would not be acceptable for bioethicists to say: let the biologists provide the data, give us their version of the facts, and we will provide the ethics. It would not be decent, because bioethicists cannot allow themselves the laziness of "believing" what biologists say with the faith of a charcoal burner; nor can they, without prudent inquiry, accept at face value that the biological data that they take from articles of knowledge dissemination more or less high quality, from manuals, or from specialized journals, are always objective and solid. It would not be licit for them to abdicate their own conscience.
And vice versa: the cultivators of biology, who are human beings, with their virtues and vices, made of the same moral fiber as others, must take great care to ensure that their work, publications and declarations are ethically responsible and upright. In day-to-day reality, there is little practical and sincere recognition among scientists that ethics encompasses their entire work, that it should inform their work and their ambitions. Rather, they tend to regard ethics as a hindrance that slows down their research. It is not easy for them to listen to ethicists, not only because they ordinarily live too fast, but because many are convinced to the marrow of their bones that it is from science, and not from ethics or religion, that man's salvation comes.
It is not easy to play the role of ethical conscience in front of scientists. They enjoy great prestige in today's society and are often flattered by the media. Bioethics should demand one thing of them: that, overcoming any conflict of ideological and not only economic interests, they should ensure that the information they provide to society and, especially, to bioethicists, is truthful, distinguishing between what is real and what is desired or imagined. After all, they cannot forget that the biology of bioethics is a serious matter.
Because it concerns them directly, bioethicists cannot disregard the need to take care of the good quality of the biology they use. They cannot plead ignorance. They will, of course, try to be friends of biologists, but also friends of the truth. Their lives depend on it. Therefore, an important part of the bioethicists' work is to seek dialogue with scientists, to work with them to identify, refine and validate the biological concepts and data they need for their programs of study: not as passive and acquiescent listeners, but as critical intellectuals. They must do this on a regular, continuous basis, because they must always update and reconsider the meaning of the data they handle. In this way they will not run the risk that the bioethical speech may degrade and negatively influence people's way of life.
To conclude this first part of my talk, I would like to add two points.
The first point is to emphasize the idea that the in-depth study of the relevant biological data is of primary importance in bioethics in the Catholic tradition. With enviable simplicity Cardinal Ratzinger said it: "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 in the light of faith and reason. We cannot forget that, in the Catholic tradition, grace does not destroy nature, but recognizes it, respects it and perfects it.
The second point, which is somewhat autobiographical, is to point out that what I have said so far is, at bottom, a self-criticism. I too, like everyone else, let myself be guided by the dominant opinion, I trusted it, I neglected my critical duty. And only recently have I come to see clearly that not investigating in depth, neglecting the critical function of biomedical science, has calamitous consequences.
In what follows, I am going to present some ideas of which I have recently become aware. Perhaps, for me, a little late. That is why I am communicating them with an accent of urgency that, at times, may seem a bit passionate. I do so with the sincere desire to open up horizons to the young.
Uses and abuses of the data scientific
I am going to refer, as stated in the second part of degree scroll of this talk, to some abuses to which the data scientists who have placed themselves in the hands of bioethicists have been subjected. Talking about abuses may seem harsh, but it is not. The truth is that, among the scientists who played an important role in the human reproductive revolution, there were many who put their undoubted scientific expertise and social influence at the service of their utilitarian, efficiency-oriented ideology, and sacrificed the truth to it. In the conflict of interests between their scientific objectivity and their sociobiological projects, the latter prevailed, and they did not hesitate, probably with the best of intentions, to give a biased orientation to their programs of study and experiments, to interpret their data in a rigged way.
A sample button will suffice to prove this purpose of manipulating the data of science. Christopher Tietze, one of the great minds of contraception, in an international meeting on IUDs, held in New York in 1964, warned that "both theologians and jurists have always accepted as factual the dominant consensus of the biologists and physicians of the day. If we can agree with agreement physicians and biologists that gestation, and therefore life, begins with implantation, our brothers in the other Schools will listen to us". As is well known by the results that can be seen today, they did so. And very soon, many theologians, jurists and bioethicists had adhered to the new consensus and incorporated it into theology, law and bioethics. The new and official scientistic version, especially that disseminated by the expert activists of the new ideology, has taken hold of public opinion. In society, what prevails is to say that life begins with implantation. The pathetic efforts of human embryologists, of embryology professors in medical schools, to restore the truth of the human embryo and regain prominence in the social discussion have been ineffective, they have not succeeded in invalidating the false consensus of the establishment.
Before continuing, a digression. When in Spain, an example that touches us closely, legislation was passed in 1988 on assisted reproduction, our deputies -as stated in the long preamble of Law 35 of that year- had committed themselves to "adjust their work to the biological truth of our times". This meant that perhaps they had read the report of the Special Commission for the Study of Human "in vitro" Fertilization and Artificial Insemination, the so-called report Palacios, drafted at the request of the Bureau of congress in November 1984, and C by plenary session of the Executive Council in April 1986.
The report imported to Spain the idea of the pre-embryo as supported by the data of science. He justified it with this reasoning: it is deduced, starting from the axiomatic equation human life = individualized human being, that individualization is determined by two properties: uniqueness (being unique and unrepeatable) and unity (being only one). But the observations of science teach that the unity of the human being is contradicted in the case of chimeras (zygotic or postzygotic); and that uniqueness is contradicted in the case 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 deduced 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.
From this reasoning, not very robust in its biological or ontological content, it was concluded that "it was not unfounded to admit that during the first 14 days of development -pre-anidatory or pre-implantation phase- the embryo is not individualized, since, as a biologist put it, 'we do not know if it will be one of two or two of one'".
The members of the Special Commission, bowing to the demonstrable biological evidence, considered that, in a regulated manner, the positive manipulation of embryos in their first fourteen days of life could be authorized. Since they could not guarantee that the pre-embryos had completed the process of individualization at that time, they felt that it was not obligatory to consider them the object of protection as human beings. Without further investigation, the deputies accepted the idea of the pre-embryo and, in view of report Palacios, approved the "Palacios Law", convinced that a gradualist biology of the human being must be answered with an equally gradualist social ethics and law.
Almost a quarter of a century later, the notion of pre-embryo is still present in the laws currently in force: in the Assisted Reproduction Law of 2006 and in the Biomedical Law of 2007, research . There are no longer any scientific or ontological digressions. They limit themselves to pointing out that the concept of pre-embryo is purely juridical, and its effects are limited to the scope of application of these laws. However, they state, in passing, that the idea has taken root in our society and that it "conforms to the biological truth of our time".
At summary, the concept of the pre-embryo is still alive and well. In addition to being sanctioned by law, it has been, in one way or another, taken up by jurists, blessed by more than a few theologians, accepted by many bioethicists, embraced by almost all researchers, disseminated by journalists, acclaimed by the people. In the midst of so much acclaim, however, it has not lacked qualified critics. I close this legislative digression here
The fictitious biology of the pre-embryo
For months now, I have been studying the foundations that biologists and physicians have laid for the now massive edifice of assisted reproduction techniques. Its cornerstone is the notion of the human pre-embryo, an entity which, in the first 14 days of its existence, neither possesses biological attributes, nor claims ethical dignity, nor enjoys the legal status of human beings properly speaking: although it certainly deserves a certain measure of respect, it cannot demand for itself the respect accorded to the human individual.
This is the dominant conclusion in the world, almost monolithic. Following the path opened in 1979 by the Ethics Advisory Board in the United States, it has been adopted by bioethics committees of different denominations in practically all advanced countries. With slight variations, which do not disguise the underlying stereotype, these committees have based their reflections on the data and arguments provided by biologists. In fact, with practically no one to contradict them, except the Magisterium of the Catholic Church, the biologists presented as incontestable biological truths, that the human neo-conceived being, during the 14 days of its existence, is a newborn baby,
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It can be divided to give rise to two or more twins;
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It can be recombined, so that two pre-embryos merge into one chimera;
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They are, and must be called, pre-embryos, since the internship totality of the cells that form them are destined to build extra-embryonic Structures . Only with the appearance of the primitive streak, on day 14, does the development of the embryo proper begin in an appreciable way.
Here we come to the heart of the matter, to the biology of real-time bioethics.
We have to ask ourselves, what is the factual soundness of these assertions? Where are the observations and experiments that corroborate them? After 30 years, these questions may seem anachronistic today. I think not. They still need to be answered. I can, after critically reading hundreds of papers, give two. They are these:
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That these three statements (on monozygotic twinning, chimerization, and cellular composition of the young embryo) have been imposed as the sole and official doctrine, so that they constitute the starting point of innumerable works of bioethicists, jurists and theologians.
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That these three statements have no factual basis. They are, in particular the first one, striking examples, in plenary session of the Executive Council XXI century, of what Francis Bacon called idola tribus, universally accepted errors.
This second response of mine is, I have no doubt, shocking. I suspect that some of my listeners are beginning to doubt my mental health, to think of me as a visionary. However, I will try to show, very briefly, the futility of these three arguments.
The futility of the monozygotic twinning argument
This argument is based on the assertion that, during the first 14 days of its existence, the human pre-embryo is capable of splitting into two or more copies of itself. Although it possesses a unique and unrepeatable genome, the pre-embryo, it is said, is not yet and unequivocally an individual, because it has not yet attained individual uniqueness. Thus we know man as an individual, as indivisible. Ergo, the pre-embryo cannot enjoy human status because it has not yet reached its irrevocable individuality.
The argument is typically bioethical: it has two arms. One, philosophical, revolves around the complex concepts of the individual and the person and their ethical rank. It has caused rivers of ink to flow. I will not go into it. The other arm, biological, confronts us with the chronology of monozygotic twinning which, we are told, extends to the first 14 days.
Today's academic biology assures us that the ability to twin begins the day after fertilization, when the zygote divides into the first two blastomeres, and is extinguished on day 14, when the primitive streak is formed. Within these two weeks - he adds - the different structure of the fetal envelopes reveals which day the division took place. This is now a classic calendar, although with curious variations from one author to another: cleavage at the stage of blastomeric segmentation, days 2 and 3, gives rise to dichorionic-diamniotic twins. Excision of the inner cell mass of the blastocyst before the beginning of training of the amnion (days 4 to 8) results in monochorionic-diamniotic twins. If, which rarely occurs, cleavage is delayed and takes place between days 9 and 13, monochorionic-monoamniotic twins are formed. Finally, even later cleavage of the embryonic outline, on or after day 14, is usually incomplete and results in the production of Siamese, conjoined twins. This description is usually narrated in an assertive style, as if describing facts.
But do they correspond to true facts, to events that have happened as they are told to us? The answer is that we do not know. The cited calendar was born from a hypothetical model , imagined in 1922 by G. W. Corner, and published in a article on twinning in the pig. The model related the structure of the fetal membranes (chorionicity, amnionicity) to different hypothetical moments of embryonic duplication. The author presented it as a speculative exercise, as a mere suggestion. He introduced it at the end of the discussion of his article with these words: "I am now going to indulge in a brief exercise of imagination on the morphogenesis of human monochorionic twins". The hypothesis was not absolutely original, since Corner was able to translate into imagined time coordinates the topographical coordinates that, before him, had been imagined to explain monozygotic twinning by Kölliker, Schultze and Newman.
Corner's ingenious, brilliant theory became consolidated orthodoxy over the years. It was enriched with the inclusion of dizygotic monozygotic twins (in 1922, it was thought that dizygotic twins were without exception dizygotic). Today it is an official icon, an undisputed paradigm, and a dogma that has not generated heretics. And yet Corner himself, 33 years later, in 1955, continued to recognize its artificial, speculative character: "embryologists and obstetricians have constructed with pencil and paper the morphological theory of uniovular twinning, tracing the different modes that the zygote could follow to develop two embryos in the end. All this is in the manuals. It has been worked out, however, by mere conjecture from the structure of the placenta and the fetal envelopes ..."
No one, to this day, has corroborated the theory with evidence. But it continues to enjoy general credibility. To my knowledge, no one out there has had the audacity to question it. The consequences of such complacent conformism are, however, plain to see: there has been no research, we are where we were in 1922: at the starting line. It seems that at the origin of every research someone has to raise a doubt, to ask a question. But no one has done so here. It is unheard of that, in a world as innovative and progressive as that of biomedicine, a theoretical model has not been corroborated or refuted for more than eight decades. It is as if we were in the time of Ptolemy's geocentric astronomy.
There is, however, an excuse, an explanation: no one has observed, nor will probably ever be able to observe, in vivo, the process of embryo cleavage that takes place in the woman's tube or uterus. Nevertheless, hundreds of thousands of human zygotes, morulae and blastocysts have been examined in vitro in the clinical field of assisted reproduction, internship . And no one has provided data, let alone reliable data , on the chronology of twinning, even though IVF causes an increase in monozygotic twinning by mechanisms that have not yet been elucidated. There are many articles published on this phenomenon and its possible causes. But none of them have been proven. In particular, no progress has been made in clarifying the moment at which embryo cleavage occurs.
We continue, at internship, to have no real descriptions of the process of human twinning. There appeared in Fertility & Sterility, September 2005, a poster graduate "Challenge to a traditional dogma: Two cases of late monozygotic division appearing as dichorionic twinning". I said to myself: it seems that the attacks on Corner's outline are finally starting. I lacked time to send an e-mail to the authors. It was disappointing: they replied that they had never followed these cases and would not publish them in detail. A few weeks ago, last December, Mio and Maeda published in Am J Obstet Gynecol some slow-motion videos of the changes observed in human embryos cultured in vitro. They are spectacular. One of them shows two blastocysts in each of which two inner cell masses had formed. But the video is incomplete (the first few days are missing) and only captures part of the thickness of the blastocyst. It does not clarify how and 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 with twinning.
I am hopeful that Corner's venerable model will gradually fall apart. It does not take into account the spatial complexity of the embryo. Perhaps in human embryology also operates a law similar to that of crystallography, which states that, above a certain level of complexity, crystal twinning is no longer possible. It is more logical to suspect that twin cleavage occurs in the first, or in the first few blastomeric divisions. We know that the embryo already in its early stages has poles and planes, that it 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 two new and complete systems of bodily symmetry, two sets of axes in the three directions of space. We know that, in the embryo, molecular decisions exist long before their morphological effects are manifested. It is in the first days, while the embryo is still inside the pellucida, that it decides molecularly the axes and planes of the body, and we know that their formal consequences only become visible after hatching.
If twinning were already done at the first blastomeric division, many ontological problems would be solved and we would recover for the embryo a simple morphogenesis: each twin could decide its body axes as a single zygote decides. But this is not seen because we are not able to appreciate fissures between separate morulae or blastocysts. Perhaps, in the future, molecular marker maps will be able to show us that from the beginning there are two where now we see only one.
In conclusion: The chronology of the orthodox model designed by Corner remains today a mere hypothesis, never demonstrated. I think it can be affirmed that it is biologically and bioethically abusive to wield it as support for the tremendous assertion that the beginning of human life should be delayed to 14 days after fertilization. It is, I insist, a disproportionate, despotic inference.
The futility of the argument of tetragametic chimeras
This argument in favor of the pre-embryo idea is very apparent, it seems to have a lot of persuasive force. It says that two dizygotic embryos can fuse, amalgamate, into a single embryo during their first 14 days. If this is so, there is no choice but to recognize that, in these two weeks, the individuality of the embryo is not determined, it remains in a fluid state, still pending to be definitively fixed. The fact that these two embryos have different pairs of sex chromosomes can result in hermaphrodite or genitally ambiguous individuals, which adds a touch of drama to the case.
What valid information do we have today on human chimeras? What we have is, besides being scarce, extremely complicated, since it is very difficult to distinguish, even with the most advanced genetic analysis procedures available, between genuine chimeras and certain forms of genetic mosaicism.
Chimeras and mosaics are organisms in which mixed cell populations of different genotypes coexist. On paper, the definitions of mosaics and chimeras are precise. In mosaics, the different cell lines come from a single zygote: they are the offspring of a single cell lineage, from which populations of different genotypes originate as a result of genetic or chromosomal errors (gene mutations, mitotic disorders) produced after fertilization.
In contrast, a chimera Genetics is an organism in which cell populations from two or more previously independent individuals coexist. There is a B variety of chimeras. Many of them are Degree minimal and are called microchimerisms. Microchimerism is very common. It occurs in subjects who have been transfused blood or have received a transplanted organ. Also, and more frequently, 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. Between monochorionic twins, in whose placentas there are vessels communicating their two circulations, an active cellular exchange may occur. These twins are always hematological chimeras and often of other tissues.
Very infrequent cases resulting from fertilization errors are also called chimeras, although improperly: 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 between some of these chimeras, in the improper sense, and the chimeras in the strict sense, the chimeras by aggregation of two embryos.
As each of the amalgamating embryos results 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 in the last five decades some 30 suspected cases have been published, upon re-examination with modern, more demanding criteria, it has been found that only five or six have shown the genetic markers required today to accept their tetragametic origin. This is, therefore, a topic for which we have little factual information.
But what interests us here, from the point of view of the biology of bioethics, is not so much to know whether there are few or many tetragametic chimeras, but rather at what moment the two embryos fuse into one: whether the capacity to amalgamate lasts one day, or a few days, or all 14 days. Some experimenters have succeeded in amalgamating animal blastocysts of 5 or 6 days: very colorful animals are born from these chimeras, including hybrids of more or less closely related species.
Recall that the important question is the one that asks data contrasted on the chronology of the training of human tetragametic chimeras. It says: how long can the fusion of two human embryos into one take place?
There is no answer: neither in the very few original papers on human tetragametic chimeras, nor in the most recent review articles, have I been able to find data of precise chronology: it is always said to occur very early. The schemes employ four-cell morulae. It does not go beyond that. In contrast to the abundance of supposed dating of monozygotic twinning, there is neither data nor hypothesis here.
As in the case of the preceding argument, this flimsy and premature argument of chimeras does not seem to have, for an impartial observer, the strength to support the idea of the pre-embryo. It will be necessary to wait to have data certain, not supposed, of the corresponding chronology. It seems, however, that there is a tendency in the most recent bibliography to suspect that many chimeras are zygotic, that is to say, they are result of a fertilization error. For the moment, this is an argument written in the sand.
The futility of the argument of the extraembryonic destiny of the preembryo
This argument maintains that, in the first two weeks, the internship totality of the cells that form the embryo are destined to build Structures extraembryonic, and that, by contrast, those that will give rise to the embryonic body are present in an insignificant issue . This is how Anne McLaren formulated it on many occasions: "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". There is practically no embryo, only pre-embryo.
This argument seems, from entrance, very persuasive. Its two elements enter through the eyes: the numerical data of the cell populations, that 999 to 1; and the abyss of value between embryo and extraembryonic Structures , which culminates in the ontological and affective distance that occurs, at the moment of delivery, between baby and placenta.
If we allow ourselves to be persuaded by him, we will think that, basically, using zygotes, morulae and blastocysts in research is equivalent, in the internship, to destroying trophectoderm and extraembryonic Structures , disposable both in the first 14 days of the development and in the delivery of the secondaries.
But are these statements built on objective data or on rhetorical figures? Let's look at the numbers first. Those cited by McLaren are not convincing. It does not seem permissible, when very serious ideas are being discussed, to move the numbers a leap of magnitude, that it makes no difference whether a cell population is 1% or 1‰, that it varies from 1 to 10, as if nothing happened. That seems more like a rhetorical resource than a quantitative reasoning Is there at the bibliography data that corroborate, in the human embryo, the figures offered by McLaren?
McLaren herself, who had insisted on the need for an "embryonic numerology", could not ignore that, while cells can be counted in the human embryo, in blastocysts cultured in vitro, the quotient moves between 20/100 and 50/100, far from 1/100 or 1/1000. Of post-implantation human embryos older than seven days, there are a few isolated estimates that are methodologically unreliable, since they do not count cells, but weigh them. It is known that the trophoblast proliferates very aggressively when invading the endometrium, but the inner cell mass itself also very rapidly increases the issue of its cells to form the epiblast in preparation for gastrulation.
Let us now consider the second part of the argument, which highlights the difference in dignity between embryonic tissue and extraembryonic tissues. This argument seems to assert that in the first two weeks there is a gulf between the extraembryonic and embryonic cellular compartments, which are two separate, even antagonistic, cell populations. The reality is that both tissues need each other. Thanks to the exchange of molecular signals that circulate in both directions and play a decisive role in the orderly activation and braking of processes, the embryoblast and the so-called extraembryonic Structures actively influence and stimulate 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 separated, embryonic stem cells can be cultured, but an integrated embryo cannot develop.
Moreover, the extraembryonic Structures not only perform these essential functions for the development, but are also the niche in which very important tissues for the construction of the individual are born. The yolk sac, first, and the placental trophoblast, later, are Structures essential for the nutrition and metabolism of the embryo and fetus. Is it necessary to remember that metabolism is not an accessory function, but an essential one in a living being? The primary elements of the germ line, without which there could be no transmission of life from one generation to the next, are generated in the extraembryonic seat. In the yolk sac wall the first hematopoietic elements are formed, which then migrate to populate the body of the embryo, to build the cells of the blood and those of the immune system. The humble allantois is the structure that sets angiogenesis in motion in the embryo: the vessels of the fetal cord and placenta, the vascular connection between placenta and embryo derive from this training. At summary: without these tissues that immigrate from the "extraembryo" into the body of the embryo, we would not be able to move forward.
To speak with little appreciation of extraembryonic formations is to despise the embryo itself. The argument is fallacious, ineffective. To say that the extra-embryonic Structures are discarded at birth is simply an unfair and ignorant appreciation of the embryology of the first days.
It is time to conclude. It seems to me that the story I have told is not one you hear every day. I did not want to provoke surprise, but responsibility. I would like my intervention today to promote in everyone, especially in those who are now receiving the degree scroll Master's degree, the decision to participate with responsibility in the discussion of the capital issues of bioethics, without neglecting the biology of bioethics. It will be better to study in a team than alone, giving bioethics its interdisciplinary character.
It is not good to repeat the past, a time, which still lasts, in which biologists act like kings and dictate their theories, with such authority that legislators and theologians, jurists and bioethicists, who did not set out to critically study biology, obey them submissively. We are still paying the price.
Thank you for your attention.