o HumanBe


International Journal of Sociology and Social Policy

The question as to when the physical material dimension of a humanbeingbegins is strictly a scientific question, and fundamentally should be answered by human embryologistsnot by philosophers, bioethicists, theologians, politicians, x-ray technicians, movie stars, or obstetricians and gynecologists. The question as to when a humanpersonbegins is a philosophical question. Current discussions on abortion, human embryo research (including cloning, stem cell research, and the formation of mixed-species chimeras), and the use of abortifacients involve specific claims as to when the life of every human being begins. If the science used to ground these various discussions is incorrect, then any conclusions will be rendered groundless and invalid. The purpose of this article is to focus primarily on a sampling of the scientific myths, and on the objective scientific facts that ought to ground these discussions. At least it will clarify what the actual international consensus of human embryologists is with regard to this relatively simple scientific question. In the final section, I will also address some scientific myths that have caused much confusion within the philosophical discussions on personhood.

Getting a handle on just a few basic human embryological terms accurately can considerably clarify the drastic difference between the scientific myths that are currently circulating, and the actual objective scientific facts. This would include such basic terms as: gametogenesis, oogenesis, spermatogenesis, fertilization, zygote, embryo, and blastocyst. Only brief scientific descriptions will be given here for these terms. Further, more complicated, details can be obtained by investigating any well-established human embryology textbook in the library, such as some of those referenced below. Please note that the scientific facts presented here are not simply a matter of my own opinion. They are direct quotes and references from some of the most highly respected human embryology textbooks, and represent a consensus of human embryologists internationally.

To begin with, scientifically something very radical occurs between the processes of gametogenesis and fertilizationthe change from a simplepartof one human being (i.e., a sperm) and a simplepartof another human being (i.e., an oocyteusually referred to as an ovum or egg), which simply possess human life, to a new, genetically unique, newly existing, individual, whole living humanbeing(a single-cell embryonic human zygote). That is, upon fertilization, parts of human beings have actually been transformed into something very different from what they were before; they have been changed into a single, whole human being. During the process of fertilization, the sperm and the oocyte cease to exist as such, and a new human being is produced.

To understand this, it should be remembered that each kind of living organism has a specific number and quality of chromosomes that are characteristic for each member of a species. (The number can vary only slightly if the organism is to survive.) For example, the characteristic number of chromosomes for a member of the human species is 46 (plus or minus, e.g., in human beings with Downs or Turners syndromes). Every somatic (or, body) cell in a human being has this characteristic number of chromosomes. Even the early germ cells contain 46 chromosomes; it is only their mature forms - the sex gametes, or sperms and oocytes - which will later contain only 23 chromosomes each..1Sperms and oocytes are derived from primitive germ cells in the developing fetus by means of the process known as gametogenesis. Because each germ cell normally has 46 chromosomes, the process of fertilization can not take place until the total number of chromosomes in each germ cell are cut in half. This is necessary so that after their fusion at fertilization the characteristic number of chromosomes in a single individual member of the human species (46) can be maintainedotherwise we would end up with a monster of some sort.

To accurately see why a sperm or an oocyte are considered as only possessing human life, and not as living human beings themselves, one needs to look at the basic scientific facts involved in the processes ofgametogenesisand offertilization. It may help to keep in mind that the products of gametogenesis and fertilization are very different. The products of gametogenesis are mature sex gametes with only 23 instead of 46 chromosomes. The product of fertilization is a living human being with 46 chromosomes. Gametogenesis refers to the maturation of germ cells, resulting in gametes. Fertilization refers to the initiation of a new human being.

As the human embryologist Larsen2states it,gametogenesisis the process that converts primordial germ cells (primitive sex cells) into mature sex gametesin the male (spermatozoa, or sperms), and in the female (definitive oocytes). The timing of gametogenesis is different in males and in females. The later stages of spermatogenesis in males occur at puberty, and continue throughout adult life. The process involves the production of spermatogonia from the primitive germ cells, which in turn become primary spermatocytes, and finally spermatidsor mature spermatozoa (sperms). These mature sperms will have only half of the number of their original chromosomesi.e., the number of chromosomes has been cut from 46 to 23, and therefore they are ready to take part in fertilization.3

Oogenesisbegins in the female during fetal life. The total number of primary oocytesabout 7 millionis produced in the female fetus ovaries by 5 months of gestation in the mothers uterus. By birth, only about 700,000 - 2 million remain. By puberty, only about 400,000 remain. The process includes several stages of maturationthe production of oogonia from primitive germ cells, which in turn become primary oocytes, which become definitive oocytes only at puberty. This definitive oocyte is what is released each month during the females menstrual period, but it still has 46 chromosomes. In fact, it does not reduce its number of chromosomes until and unless it is fertilized by the sperm, during which process the definitive oocyte becomes a secondary oocyte with only 23 chromosomes.4

This halving of the number of chromosomes in the oocytes takes place by the process known asmeiosis. Many people confuse meiosis with a different process known as mitosis, but there is an important difference.Mitosisrefers to the normal division of a somatic or of a germ cell in order to increase the number of those cells during growth and development. The resulting cells contain the same number of chromosomes as the previous cellsin human beings, 46.Meiosisrefers to the halving of the number of chromosomes that are normally present in a germ cell - the precursor of a sperm or a definitive oocyte - in order for fertilization to take place. The resulting gamete cells have only half of the number of chromosomes as the previous cellsin human beings, 23.

One of the best and most technically accurate explanations for this critical process of gametogenesis is by Ronan ORahilly,5the human embryologist who developed the classic Carnegie stages of human embryological development. He also sits on the international board ofNomina Embryologica(which determines the correct terminology to be used in human embryology textbooks internationally):

Gametogenesisis the production of [gametes], i.e., spermatozoa and oocytes. These cells are produced in the gonads, i.e., the testes and ovaries respectively. ... During the differentiation of gametes, diploid cells (those with a double set of chromosomes, as found in somatic cells [46 chromosomes]) are termed primary, and haploid cells (those with a single set of chromosomes [23 chromosomes]) are called secondary. The reduction of chromosomal number ... from 46 (the diploid number or 2n) to 23 (the haploid number or n) is accomplished by a cellular division termed meiosis. ...Spermatogenesis, the production of spermatozoa, continues from immediately after puberty until old age. It takes place in the testis, which is also an endocrine gland, the interstitial cells of which secrete testosterone. Previous to puberty, spermatogonia in the simiferous tubules of the testis remain relatively inactive. After puberty, under stimulation from the interstitial cells, spermatogonia proliferate ... and some become primary spermatocytes. When these undergo their first maturation division (meiosis 1), they become secondary spermatocytes. The second maturation division (meiosis 2) results in spermatids, which become converted into spermatozoa.6

Oogenesisis the production and maturation of oocytes, i.e.; the female gametes derived from oogonia. Oogonia (derived from primordial germ cells) multiply by mitosis and become primary oocytes. The number of oogonia increases to nearly seven million by the middle of prenatal life, after which it diminishes to about two million at birth. From these, several thousand oocytes are derived, several hundred of which mature and are liberated (ovulated) during a reproductive period of some thirty years. Prophase of meiosis 1 begins during fetal life but ceases at the diplotene state, which persists during childhood. ... After puberty, meiosis 1 is resumed and a secondary oocyte ... is formed, together with polar body 1, which can be regarded as an oocyte having a reduced share of cytoplasm. The secondary oocyte is a female gamete in which the first meiotic division is completed and the second has begun. From oogonium to secondary oocyte takes from about 12 to 50 years to be completed.Meiosis 2 is terminated after rupture of the follicle (ovulation) but only if a spermatozoon penetrates.... The term ovum implies that polar body 2 has been given off, which event is usually delayeduntil the oocyte has been penetrated by a spermatozoon (i.e., has been fertilized). Hence a human ovum does not [really] exist. Moreover the term has been used for such disparate structures as an oocyte and a three-week embryo, and therefore should be discarded, asa fortiorishould egg.7(Emphasis added.)

Thus, for fertilization to be accomplished, a mature sperm and a mature human oocyte are needed. Before fertilization,8each has only 23 chromosomes. They each possess human life, since they are parts of alivinghuman being; but they are not each whole living human beings themselves. They each have only 23 chromosomes, not 46 chromosomesthe number of chromosomes necessary and characteristic for a single individual member of the human species. Furthermore, a sperm can produce only sperm proteins and enzymes; an oocyte can produce only oocyte proteins and enzymes; neither alone is or can produce a human being with 46 chromosomes.

Also, note ORahillys statement that the use of terms such as ovum and eggwhich would include the term fertilized eggis scientifically incorrect, has no objective correlate in reality, and is therefore very misleadingespecially in these present discussions. Thus these terms themselves would qualify as scientific myths. The commonly used term, fertilized egg, is especially very misleading, since there is really no longer an egg (or oocyte) once fertilization has begun. What is being called a fertilized egg is not an egg of any sort; it is a human being.

Now that we have looked at the formation of the maturehaploidsex gametes, the next important process to consider is fertilization. ORahilly definesfertilizationas:

... the procession of events that begins when a spermatozoonmakes contactwith a secondary oocyte or its investments, and ends with the intermingling of maternal and paternal chromosomes at metaphase of the first mitotic division of thezygote. The zygote is characteristic of the last phase of fertilization and is identified by the first cleavage spindle. It is a unicellularembryo.9(Emphasis added.)

The fusion of the sperm (with 23 chromosomes) and the oocyte (with 23 chromosomes) at fertilization results in a live human being, a single-cell human zygote, with 46 chromosomesthe number of chromosomes characteristic of an individual member of the human species. Quoting Moore:

Zygote:This cell results from the union of an oocyte and a sperm.A zygote is the beginning of a new human being (i.e., an embryo).The expressionfertilized ovumrefers to a secondary oocyte that is impregnated by a sperm; when fertilization is complete, the oocyte becomes a zygote.10(Emphasis added.)

This new single-cell human being immediately produces specifically human proteins and enzymes11(not carrot or frog enzymes and proteins), and genetically directs his/her own growth and development. (In fact, this genetic growth and development has been provennotto be directed by the mother.)12Finally, this new human beingthe single-cell human zygoteis biologically anindividual, a living organisman individual member of the human species. Quoting Larsen:

... [W]e begin our description of the developing human with the formation and differentiation of the male and female sex cells or gametes, which will unite at fertilization to initiate the embryonic development ofa new individual.13(Emphasis added.)

In sum,a mature human sperm and a mature human oocyte are products of gametogenesiseach has only 23 chromosomes. They each have only half of the required number of chromosomes for a human being. They cannot singly develop further into human beings. They produce only gamete proteins and enzymes. They do not direct their own growth and development. And they are not individuals, i.e., members of the human species. They are only partseach one a partofa human being. On the other hand,a human being is the immediate product of fertilization. As such he/she is a single-cell embryonic zygote, an organismwith 46 chromosomes, the number required of a member of the human species. This human being immediately produces specifically human proteins and enzymes, directs his/her own further growth and developmentas human, and is a new, genetically unique, newly existing, live humanindividual.

After fertilization the single-cell human embryo doesnt become anotherkindof thing. It simply divides and grows bigger and bigger, developing through several stages as an embryo over an 8-week period. Several of these developmental stages of the growing embryo are given special names, e.g., a morula (about 4 days), a blastocyst (5-7 days), a bilaminar (two layer) embryo (during the second week), and a trilaminar (3-layer) embryo (during the third week).14

B. Scientific myths and scientific fact:

Given these basic facts of human embryology, it is easier to recognize the many scientifically inaccurate claims that have been advanced in the discussions about abortion, human embryo research, cloning, stem cell research, the formation of chimeras, and the use of abortifacientsand why these discussions obfuscate the objective scientific facts. The following is just a sampling of these current scientific myths.

Myth 1:Prolifers claim that the abortion of a human embryo or a human fetus is wrong because it destroys human life. But human sperms and human ova are human life, too. So prolifers would also have to agree that the destruction of human sperms and human ova are no different from abortionsand that is ridiculous!

Fact 1:As pointed out above in the background section, there is a radical difference, scientifically, between parts of a human being that only possess human life and a human embryo or human fetus that is an actual human being. Abortion is the destruction of a human being. Destroying a human sperm or a human oocyte would not constitute abortion, since neither are human beings. The issue is not when does humanlifebegin, but rather when does the life of every humanbeingbegin. A human kidney or liver, a human skin cell, a sperm or an oocyte all possess humanlife, but they are not humanbeingsthey are only parts of a human being. If a single sperm or a single oocyte were implanted into a womans uterus, they would not grow; they would simply disintegrate.

Myth 2:The product of fertilization is simply a blob, a bunch of cells, a piece of the mothers tissues.

Fact 2:As demonstrated above, the human embryonic organism formed at fertilization is a whole human being, and therefore it is not just a blob or a bunch of cells. This new human individual also has a mixture of both the mothers and the fathers chromosomes, and therefore it is not just a piece of themotherstissues. Quoting Carlson:

... [T]hrough the mingling of maternal and paternal chromosomes, the zygote isa genetically unique product of chromosomal reassortment, which is important for the viability of any species.15(Emphasis added.)

Myth 3:The immediate product of fertilization is just a potential or a possible human beingnot a real existing human being.

Fact 3:As demonstrated above, scientifically there is absolutely no question whatsoever that the immediate product of fertilization is a newly existing human being. A human zygoteisa human being. It isnota potential or a possible human being. Its an actual human beingwith the potential to grow bigger and develop its capacities.

Myth 4:A single-cell human zygote, or embryo, or fetus are not human beings, because they do not look like human beings.

Fact 4:As all human embryologists know, a single-cell human zygote, or a more developed human embryo, or human fetus is a human beingand that thats the way they are supposed to look at those particular periods of development.

Myth 5:The immediate product of fertilization is just an itit is neither a girl nor a boy.

Fact 5:The immediate product of fertilization is genetically already a girl or a boydetermined by the kind of sperm that fertilizes the oocyte. Quoting Carlson again:

...[T]he sex of the future embryo is determined by the chromosomal complement of the spermatozoon. (If the sperm contains 22 autosomes and 2 X chromosomes, the embryo will be a genetic female, and if it contains 22 autosomes and an X and a Y chromosome, the embryo will be a genetic male.)16

Myth 6:The embryo and the embryonic period begin at implantation. (Alternative myths claim 14 days, or 3 weeks.)

Fact 6:These are a few of the most common myths perpetuated sometimes even within quasi-scientific articlesespecially within the bioethics literature. As demonstrated above, the human embryo, who is a human being, begins at fertilizationnot at implantation (about 5-7 days), 14-days, or 3 weeks. Thus the embryonic period also begins at fertilization, and ends by the end of the eighth week, when the fetal period begins. Quoting ORahilly:

Prenatal life is conveniently divided into two phases: the embryonic and the fetal. Theembryonic period properduring which the vast majority of the named structures of the body appear, occupies thefirst 8 postovulatory weeks. ... [T]he fetal period extends from 8 weeks to birth ...17(Emphasis added.)

Myth 7:The product of fertilization, up to 14-days, is not an embryo; it is just a pre-embryoand therefore it can be used in experimental research, aborted, or donated.

Fact 7:This scientific myth is perhaps the most common error, which pervades the current literature. The term pre-embryo has quite a long and interesting history. (See Irving and Kischer,The Human Development Hoax: Time To Tell The Truth!, for extensive details and references.) But it roughly goes back to at least 1979 in the bioethics writings of Jesuit theologian Richard McCormick in his work with the Ethics Advisory Board to the United States Department of Health, Education and Welfare,18and those of frog developmental biologist Dr. Clifford Grobstein in a 1979 article inScientific American,19and most notably in his classic book,Science and the Unborn: Choosing Human Futures(1988).20Both McCormick and Grobstein subsequently continued propagating this scientific myth as members of the Ethics Committee of the American Fertility Society, and in numerous influential bioethics articles, leading to its common use in bioethics, theological, and public policy literature to this day.

The term pre-embryo was also used as the rationale for permitting human embryo research in the British Warnock Committee Report (1984),21and then picked up by literally hundreds of writers internationally, including, e.g., Australian writers Michael Lockwood, Michael Tooley, Alan Trounsonand especially by Peter Singer (a philosopher), Pascal Kasimba (a lawyer), Helga Kuhse (an ethicist), Stephen Buckle (a philosopher) and Karen Dawson (a geneticist, not a human embryologist). Note that none of these is even a scientist, with the exception of Karen Dawson, who is just a geneticist.

Oddly, the influential book by Singer, Kuhse, Buckle, and Dawson,Embryo Experimentation,22(which uses the term pre-embryo, and which contains no scientific references for its human embryology chart or its list of scientific terms), along with the work of theologian McCormick and frog developmental biologist Grobstein, was used in the United States as thescientificbasis for the 1994 National Institutes of Heath (NIH) Human Embryo Research Report.23That Report concluded that the preimplantation embryo (they, too, originally used the term pre-embryo) had only a reduced moral status. (Both the Warnock Report and the NIH Report admitted that the 14-day limit for human embryo research was arbitrary, and could and must be changed if necessary.) It is particularly in the writings of these and other bioethicists that so much incorrect science is claimed in order to scientifically ground the pre-embryo myth and therefore scientifically justify many of the issues noted at the beginning of this article. This would include abortion, as well as the use of donated or made-for-research early human embryos in destructive experimental human embryo research (such as infertility research, cloning, stem cell research, the formation of chimeras, etc.).

To begin with, it has been demonstrated above that the immediate product of fertilization is a human being with 46 chromosomes, a human embryo, an individual member of the human species, and that this is the beginning of the embryonic period. However, McCormick and Grobstein24claim that even though the product of fertilization is genetically human, it is not a developmental individual yetand in turn, this scientific fact grounds their moral claim about this pre-embryo. Quoting McCormick:

I contend in this paper thatthe moral statusand specifically the controversial issue of personhoodis related to the attainment of developmental individuality(being the source of one individual) ... It should be noted that at the zygote stage the genetic individual is not yet developmentally singlea source of only one individual. As we will see, that does not occur until a single body axis has begun to form near the end of the second week post fertilization when implantation is underway.25(Emphasis added.)

Sounds very scientific. However, McCormicks embryology is already self-contradictory. Implantation takes place at 5-7 days. The single body axis to which he refers is the formation of the primitive streak, which takes place at 14 days. McCormick often confuses these different periods in his writings. But McCormick continues:

This multicellular entity, called a blastocyst, has an outer cellular wall, a central fluid-filled cavity and a small gathering of cells at one end known as the inner cell mass. Developmental studies show that the cells of the outer wall become the trophoblast (feeding layer) and are precursors to the later placenta. Ultimately,allthese cells are discarded at birth.26(Emphasis added.)

The clear implication is that there is absolutely no relationship or interaction between these two cell layers, and so the entity is not a developmental individual yet. However, quoting Larsen:

These centrally placed blastomeres are now called the inner cell mass, while the blastomeres at the periphery constitute the outer cell mass. Some exchange occurs between these groups. ... The cells of this germ disc (the inner cell layer) develop into the embryo proper and also contribute to some of the extraembryonic membranes.27(Emphasis added.)

Similarly, it is not factually correct to state thatallof the cells from the outer trophoblast layer are discarded after birth. Quoting Moore:

The chorion, the amnion, the yolk sac, and the allantois constitute the fetal membranes. They develop from the zygote but do not participate in the formation of the embryo or fetusexcept for parts of the yolk sac and allantois. Part of the yolk sac is incorporated into the embryo as the primordium of the gut. The allantois forms a fibrous cord that is known as the urachus in the fetus and the median umbilical ligament in the adult. It extends from the apex of the urinary bladder to the umbilicus.28(Emphasis added.)

Since scientists, in trying to reach young students in a more familiar language, sometimes use popularized (but scientifically inaccurate and misleading) terms themselves, the ever-vigilant ORahilly expresses concern in his classic text about the use of the term fetal membranes:

The developmental adnexa, commonlybut inaccuratelyreferred to as the fetal membranes, include the trophoblast, amnion, chorion, umbilical vesicle (yolk sac), allantoic diverticulum, placenta and umbilical cord.They are genetically a part of theindividualand are composed of the same germ layers.29(Emphasis added.)

Consequently, it is also scientifically incorrect to claim thatonlythe inner cell layer constitutes the embryo proper.The entire blastocystincluding both the inner and the outer cell layersis the human embryo, the human being, the human individual.

Finally, McCormick claims that this pre-embryo has not yet decided how many individuals it will become, since the cells are totipotent and twinning can still take place. Therefore, they argue, there is no individual present until 14-days and the formation of the primitive streak, after which twinning cannot take place.30

However,twinning is possible after 14 days, e.g., with fetus-in-fetu and Siamese twins. Quoting from ORahilly again:

Partial duplication at an early stage and attempted duplicationfrom 2 weeks onward(when bilateral symmetry has become manifest) would result in conjoined twins (e.g., Siamese twins).31(Emphasis added.)

And even Karen Dawson acknowledges this as scientific fact in her article inEmbryo Experimentation:

After the time of primitive streak formation, other events are possible which indicate that the notion of irreversible individuality may need some review if it is to be considered as an important criterion in human life coming to be the individual human being it is ever thereafter to be. There are two conditions which raise questions about the adequacy of this notion: conjoined twins, sometimes known as Siamese twins, and fetus-in-fetu. ... Conjoined twins arise from the twinning processoccurring after the primitive streak has begun to form, that is, beyond 14 days after fertilization, or, in terms of the argument from segmentation, beyond the time at which irreversible individuality is said to exist. ... This situation weakens the possibility of seeing individuality as something irreversibly resolved by about 14 days after fertilization. This in turn raises questions about the adequacy of using the landmark of segmentation in development as the determinant of moral status.32(Emphasis added.)

It is unfortunate that the NIH Human Embryo Research Panel33did not read this particular portion of the Singeret al.book before making their recommendations about the moral status of the early human embryo.

The scientific fact is that there is no such thing as a pre-embryo in the real world. The term is a complete myth. It was fabricated out of thin air in order to justify a number of things that ordinarily would not be justifiable. Quoting ORahilly, who sits on the international board ofNomina Embryologica, again:

Theill-defined and inaccurate term pre-embryo,which includes the embryonic disk, is said either to end with the appearance of the primitive streak or to include neurulation.The term is not used in this book.34(Emphasis added.)

Unfortunately, the convenient but mythological term pre-embryo will be used to scientifically justify several of the other scientific myths to follow, which in turn will be used to justify public policy on abortion and human embryo research world-wide.

Myth 8:Pregnancy begins with the implantation of the blastocyst (i.e., about 5-7 days).

Fact 8:This definition of pregnancy was initiated to accommodate the introduction of the process ofin vitrofertilization, where fertilization takes place artificially outside the mother in a petri dish, and then the embryo is artificially introduced into the womans uterus so that implantation of the embryo can take place. Obviously, if the embryo is not within the womans body, she is not pregnant in the literal, traditional sense of the term. However, thisartificialsituation cannot validly be substituted back to redefine normalpregnancy, in which fertilizationdoestake place within the womans body in her fallopian tube, and subsequently the embryo itself moves along the tube to implant itself into her uterus. In normal situations, pregnancy begins at fertilization, not at implantation. Quoting Carlson:

Human pregnancy begins with the fusion of an egg and a sper.