Biologically, A New Human Life Begins When Fertilization is Complete
This argument wouldn't have to be made, but for science becoming post modern in some circles so that narrative counts more than facts. This has certainly been true with regard to biotechnology because some want to use human embryos instrumentally. But rather than just admit that and justify it ethically, definitions were changed, for example, claiming that an embryo only comes into being upon implantation, rather than at its beginning at the completion of fertilization. In that way--presto-chango--embryos in petri dishes could be used as so many kernels of corn.
But I looked into this issue when I was researching Consumer's Guide to a Brave New World. Every embryology text book I reviewed retained the non political definition of when human life begins, e.g. at the completion of fertilization. One is The Developing Human: Clinically Oriented Embryology (6th Ed.) (Keith Moore and T. V. N. Persaud, W. B. Sanders Company, Philadelphia, PA, 1998), which asserts:
Human development is a continuous process that begins when an oocyte is fertilized by a sperm. (page 2)More to the point, the authors write:
Human development begins at fertilization [with the joining of egg and sperm, which] form a single cell called a zygote. This highly specialized...cell marks the beginning of each of us as a unique individual.(page 18)The authors of another embryology textbook (Ronan O'Ramilly and Fabiola Muller, Human Embryology and Teratology, (Third Ed.), (Willey-Liss, New York, NY, 2001), also state on page 8 that upon the completion of fertilization:
a new, genetically distinct human organism is formed.
Since some don't want to call embryos what they are, as I pointed out in an earlier post, some politicized scientists use the word "pre embryo," as if it were something different in kind than an embryo after it implants. But scientifically, biologically, there is no such thing as a pre-embryo. Thus, the authors of Human Embryology and Teratology, in the name of scientific accuracy, place the term "pre-embryo" under the categorization, "Undesirable Term in Human Embryology," further asserting that "embryo" is the accurate and hence, "preferable term." They write further on page 88: The term "pre-embryo" is not used here [in their book] for the following reasons: (1) it is ill-defined; (2) it is inaccurate...(3) it is unjustified because the accepted meaning of the world embryo includes all of the first 8 weeks; (4) it is equivocal because it may convey the erroneous idea that a new human organism is formed at only some considerable time after fertilization; and (5) it was introduced in 1986 "largely for public policy reasons."But of course, such objective scientific analysis doesn't serve the polemic needs of some ESCR and cloning advocates.
posted by Wesley J. Smith @ 4:41 PM
22 Comments
22 Comments:
It doesn't matter what we call it or when it starts. It's all a matter of definition by humans and as we did not create it we are not entitled to define it, no matter how we define it or at what sage it starts. This is sheer human arrogance and the root of the whole problem. I'm not traditionally religious; I don't understand or care about all the hoopla over God, creationism, whatever that other theory is called, are we further evolutionary stages of apes and related to other animals (of course we are); to methat's just another version of human arrogance and insanity, presuming to scan God rather than man. None of it is necessary. It's very simple. These are not things we are supposed to see or be poking into. We did just fine and were more civilized and produced greater cultural achievements before we did. We weren't designed for all this to be visible and that tells us all we need to know. Leaving religion out of the equation, where it's unnecessary in the first place, common sense is enough to tell us not to mess with it. Remember how they used to say, "They can put a man on the moon but they can't..." We've got plenty of things to do to occupy our time, and when "science" goes in a direction like this, where it doesn't belong, the wrong people are driving the train, and the train runs over the eldery and the disabled. It's not wonderful of us to be doing this, regardless of what self-interested scientists want us to believe. It's sheer stupid. Science is a servant, not a god. Let them wash dishes and sell shoes, if they are capable of doing those things well, until and unless they get enough wisdom to be entitled to have the privilege of doing science. Most of them won't, aren't, and never will be, and without them we'll manage, and much better. This isn't a civilization we've got with them running around loose and rampant; it's a damned asylum. We want a civilization again, they have to be kept in their place.
I have a very cool white paper by Maureen Condic in PDF form on the first day after the sperm penetrates the egg--very detailed. If you want it, just tell me here in the combox and I'll send it to you by e-mail.
For what it's worth, embryos are frozen only after scientists have checked to see that fertilization was successful. (I researched this myself on-line.) They wait the requisite time and check for the two pronuclei. I found this interesting. There is no question of a situation where what is being kept frozen for possible later IVF is "not really an embryo yet," even if one takes an embryo not to exist until fertilization is complete.
This reminds me of my own research on the Terri Schiavo issue. During a core biology course in college, I read in a biology textbook that dehydration causes brain tissue to collapse as cerebral fluid is depleted and blindness near the end, both of which were noted in the Schiavo autopsy and cited as evidence for Michael Schiavo's position. The fact that these are basic results of dehydration didn't seem to carry weight in any of the discussion that was publicized, despite one being able to go to something as simple as a common variety biology book and get that information.
SAFEpres: People don't want to know what they don't want to know.
There seems to be a trend spreading in which people draw a circle just big enough to include themselves, then annouce that everyone outside the circle can be exploited for the benefit of those inside.
I'm a healthy adult? Embryos, the elderly, and the disabled should be fair game for human experimentation so that I can live another X years. They're not really "human" anyway.
I need an organ transplant? Poor people and prisoners in faraway countries deserve their livers and kidneys less than I do.
Cities sometimes seem crowded? There are too many people. Some of those other folks should die off - but never me.
I'm starting to think that the defining feature of the 21st century's philosophy will be naked selfishness.
Thank you for posting this. I'm getting awfully tired of people dismissing this as though it's a religious belief.
This is an excellent post and really getting to the heart of the matter. Thank you. I think this is what society needs rather than fluffy rhetoric about curing diseases. (who doesn't want a cure for MS???)
The definition given by O'Ramilly and Muller has been criticized. This is based on work with sea urchin embryos. However, fertilization to zygote of a sea urchin is not similar to that of a human egg fertilization to zygote. The crux of this complaint lies in the statement that a genetically distinct human organism is formed. Firstly, there is not a scientific consensus as to what an organism is (is a virus an organism?). But the real problem is the error with the statement of genetic distinction. In the case of a sea urchin fertilization, this appears to be true. In the case of human fertilization, this appears not to be true. What's interesting is that a human, so far as we currently know, is not genetically distinct at fertilization. In humans, unlike sea urchins, this occrus at the first mitotic division. The displacement of the second polar body is necessary for a unique genetic footprint. In human fertilization, all chromosomes line up on the mitotic plane, later to be segregated. Well, I'm superfluously babbling now in limited space and time. Basicially, complete genetic distinction cannot be absolutely determined until about 12 or so (at the shortest) days after zona pellucida penetrance. Some have dubbed this the "twinning argument". I see merit and drawback to this argument.
I am somewhat familiar with the Moore & Persuad text and have similar concerns, though did not find as much disagreement. From their definitions, I would actually contend that human development then begins at progenitor gamete formation. But I do not accept their definitions. I would disagree that a zygote marks the beginning of a "unique individual". I would suggest a blastocyte as a genetically unique cellular life. I agree that development is a continuous process. I would caution against confusing "development" or genetic distinction from "human life".
I would point readers to this companion text by Dr. Scott Gilbert (PhD). I am unsure if readers will have access to this. I have some questions with it, but overall, I think it is a nice presentation of some of the disagreements and ideas (not theories) among scientists.
http://8e.devbio.com/article.php?id=162
* on a side note, there is a 1991 citation perhaps dealing with what is a "pre-embryo".
Dana: It is also worth noting regarding this issue that the prestigious British science journal Nature published an article describing how the mammalian body plan “starts being laid down immediately” upon fertilization. “Your world was shaped in the first 24 hours after conception,” the Nature article asserted. “Where your head and feet would sprout, and which side would form your back and which your belly, were defined in the minutes and hours after sperm and egg united.” In other words, the newly fertilized one cell embryo is already a unique human life, not merely the “naïve sphere” or “featureless orb” as scientists once thought.
Helen Pearson, “Your Destiny, From Day One,” Nature, July 8, 2002.
"What's interesting is that a human, so far as we currently know, is not genetically distinct at fertilization. In humans, unlike sea urchins, this occrus at the first mitotic division. The displacement of the second polar body is necessary for a unique genetic footprint. In human fertilization, all chromosomes line up on the mitotic plane, later to be segregated. Well, I'm superfluously babbling now in limited space and time. Basicially, complete genetic distinction cannot be absolutely determined until about 12 or so (at the shortest) days after zona pellucida penetrance."
Hold on just a minute: Human genetic uniqueness _is_ determined, including the things you mention, _long_ before 12 _days_ after the sperm penetrates the zona pellucida! The genome is determinate 30 _mintes_ after penetration, with the completion of maternal meiosis and the end of the transient triploid state. No twelve days!
The twinning argument is actually a different argument--namely, the argument that even though the embryo is genetically distinctive and determinate by the end of fertilization, since it _could in theory_ divide and asexual reproduction (twinning) could take place for a couple more weeks, it is not yet a human organism. But that has nothing to do, as far as I know, with the suppression of the second polar body or the completion of meiosis, which are long finished with before then. The first mitotic division occurs 20-25 _hours_ after the sperm penetrates.
George and Tollefson address and refute the "twinning" argument (and every other challenge to the personhood of the human embryo) in EMBRYO: A DEFENSE OF HUMAN LIFE. It's a great source.
Speaking of sources, do you have a list, Wesley? I keep a list of about eleven or twelve texts that explain the facts of fertilization (as you have here), but I'd always love to buttress that list with more.
The Condic paper I mentioned is the best thing I've ever seen. Really detailed.
Hmmm, how can the possibility of a twin still be a factor, yet genetic uniqueness is absolute? And what is genetic uniqueness anyways and why should that be a marker of personhood? The genome is not determined after 30 minutes. Transposable elements, epigenetics, retrotranspons, etc. These events can occur throughout the lifespan of cellular and organismal life forms. If one is looking for genetics to determine personhood of a human, I caution they are barking up the wrong tree.
The George and Tollefsen work (both philosophers) fails to convince many in the scientific community; so they refute it, but not very convincingly.
As for twinning and polar bodies, they are separate issues. I will have to elaborate and babble here. The point of each of these phenomemon, however, is to highlight the complex developmental process of a fertilized egg (immediately following zona pellucida penetrance), to embryo/zygote, etc, etc. In the case of the polar body, it appears (though an experiment performed tomorrow, if not already done, may disprove this) that it needs to be displaced. I have heard speculation that polysomy may be a result of this not proceeding "correctly" (although what "correct" is, is hard to say) and I'm skeptical of this for other reasons. Anyways that is one instance whereby "fertilization" as it were, may not be a good marker for true genetic identity (one could use the term "genetic determination" as following the cortical reaction and calcium release, polyspermy appears to be slowly blocked and the secondary oocyte is genetically determined). The twinning argument is to highlight another point in the development at which genetic identity may be in doubt.
And last but not least, the Helen Pearson news feature is not in the least convincing that personhood is established within 24 hours, or some other "brief" timespan. In this feature, Pearson highlights the work done by Gardner that, in short, demonstrates the embryo has an axis of development that emerges much sooner than biologists previously thought. The consequences of this axis of development suggest that where the various cells and tissues in an embryo develop are determined very soon following fertilization. (Personally, I wouldn't be surprised if such an axis isn't determined very early - we know that the chromosomes must be aligned, yet not combined, for the first mitotic division following the cortical reaction). To draw the conclusion from Pearson's feature that "in other words the newly fertilized one-celled embryo is already a unique human life" seems far-fetched to me. The article (referring to Gardner) deals primarily with the laying out, if you will, of emergent axis. I do not see the connection of an emergent axis, which cause development limitations/certainties as being a defining moment of "human life". For example, it has long been known that hamster eggs which have had the zona pellucida enzymatically removed can be fertilized by human sperm. (indeed this used to, and may still be in some cases, used as a test to determine the 'viability' of human sperm - zona pellucida penetrance test). Fertilization occurs, by definition, but development does not. (some referred to this as a 'humster' hybrid). Furthermore, the problem with using this axial assignment that Gardner uncovers and Pearson highlights for a definition of personhood or organismal uniqueness is that axial assignment occurs in biology BEFORE fertilization in many organisms - fruit flies and frogs for example. The case is interesting for amphibians whereby the sperm entry point determines polarity, but I digress. The point being, that perhaps in humans this axial assignment is already laid out in the egg itself and the point of entry of the sperm must be correct - in other words, it's NOT the first sperm to reach the egg, but rather the first "healthy" sperm to reach the right PLACE on the egg AND successfully bind, because this axis is already cellularly established.
And finally, the piece by Pearson is not an article. With the journal "Nature", articles are defined as 'original reports' in section 1.1. Pearson's work falls under section 1.4 as "other contributions to 'Nature'". I only say this because I see this used in the media a bit when it is claimed "an article in 'Nature'..." - when said piece is in fact, not an article but rather a "letter", "news and views", "commentary", etc, etc.
At any rate, I have enjoyed these posts.
On a totally different note, I came across this piece in the NYT by Frank Rich about the "culture climate" and "culture wars". Rich suggests it's over/in remission and the conservative right lost. I'm not a fan or Rich and not sold on his conclusion. However, I really have not found many people to discuss this piece.
Are ESC part of the "culture war"? Is such a "war" over? (I hate using the term "war" here because that word connotes a type of acceptable/necessary killing and destruction. I believe "debate" is better here). Should the issues be chosen carefully? Can "conservatives" battle gay marriage, ESC, cloning, prayer in schools, etc all at the same time? Do we have no luxury for such debate in a time of economic crisis? What are, or should be, the issues of the culture debate?
Might this piece be a good entry on the blog, Mr. Smith???????????
http://www.nytimes.com/2009/03/15/opinion/15rich.html
Dana: One election does not settle anything for all time. Plus, the "culture wars" addressed here tend to cut across the liberal and conservative divides, not that a two dimensional view of them would notice. Example, assisted suicide is very much opposed by the disability rights movement, that tends to be very liberal in its policits.
As to whether he is worth posting here: No.
"hamster eggs which have had the zona pellucida enzymatically removed can be fertilized by human sperm"
Not exactly: "The injection of human sperm into hamster eggs is an inappropriate in vitro model for human fertilization because hamster fertilization relies on a maternal centrosome, and human sperm do not undergo microtubule assembly in hamster eggs..."
http://www.biolreprod.org/cgi/content/full/62/3/557
Human completion of fertilization is determined in a specific way--by the presence of both pronuclei. This was not happening in the hamster eggs, apparently, so nothing analogous to human fertilization completion was happening.
I said, "fertilization occurs by definition." This is correct by the Alberts and Watson definition (which I should have mentioned), which defines it as gamete union (a binding event). Other biologists, such as Campbell, define it (fertilization) as not only gamete union, but the process leading to a diploid cell.
Lydia, you disappoint me so much. You cherry pick one definition and build your case around it (as I did in that one statement). If you REALLY want to impress me, tell me why the fertilization definition of binding is an inferior definition to either diploid formation, or pronuclear formation or migration, or 2nd polar body displacement, or chromosomal alignment, or membrane depolarization, or Ca release, or polyspermy block, or centriole formation, or well, I'll stop there (and I won't say which definition I favor cause it changes daily). And most importantly, tell me why this defintion of pronuclear formation should NOT change and is superior to all aforementioned and unmentioned phenomenon, even if new data becomes available. But really, none of that matters, since these questions are so easily answered, it should be a cinch to biologically defend, and not just cite, why a zygote or blastocyte is "human life" and why that definition should be imposed on others/society (the latter is an easier argument to defned, I think, but that's just my opinion). After all, it's not like biologists disagree on that former one, wait a minute, or do they...
By the way, re-read the paper, I propose you are confusing a model with a process, and using said model to help define a process and such process cannot be defined by an event.
Actually, I said that fertilization is _determined_ to have happened by pronuclear formation. I didn't actually say it is defined that way, though I know some do so define it. But that's how you tell that it is completed. And in the hamster case there cannot be in principle such a determination because there is no process headed in that direction, because all the human sperm does is to activate the egg for a while, and in hamster eggs evidently they can go on for a little while maternally, longer than human eggs can. No challenge there to the claim that a new human life is present when fertilization is complete, because the two processes aren't the same process biologically.
And I propose in any event that you are trying to confuse the issue, because you know quite well (since you know a lot about this) that there is a continuity of development between the zygote and...you. You know that better than I do, probably.
Actually, perhaps not, Lydia, this is not my area of ken. I'm skeptical that these definitions are so easy and concrete, that's all, really.
Here is an example of such a nebulous area, to me, anyways. (you may not be able to access this article, though) This is an interesting one to wrap the head around for a few days (or in my case probably for months on end):
http://www.liebertonline.com/doi/abs/10.1089/scd.2009.0004
I'm not closed in principle to the possibility of parthenogensis in humans. The truth is, I think, that we just don't know enough right now scientifically to say definitively one way or another. I think it would be unethical. When I say, "I'm not closed in principle" I don't mean to _doing_ it, I mean to its being _possible_, i.e., to the idea that parthenotes are indeed human zygotes, although it may be damaged ones.
Those parthenotes should be haploid, from the depiction here. What is more interesting to me is that they were able to develop, albeit from the data quite poorly. To me, this really blurs the line - it's like a non-embryo blastomere or zygote (what???), or are these "alternative" embryos? And why only a third, what allows them to be different (egg maturation, external factors, etc???) Regardless, it seems impossible for these to develop any further as is, I presume. It'll take me a long time to sort this one out...
I like your post, but you are wrong to leave out "being" and to say "...when fertilization is complete." Biologically, a new human *being's* (because it exists) life begins at the onset of fertilization.
It seems like a minor point, but technically the real beginning is when sperm and egg first fuse.
Someone already referenced the white paper from The Westchester Institute by Maureen Condic.
It's an excellent and thorough paper.
I was e-mailed the following comment by Dianne Irving, PH.D, who asked me to post as a comment to this thread:
Wesley – Dianne here. Thank you for this excellent presentation. Superb that you point out that there is no such thing as a “pre-embryo” – the term was formally rejected by the international Nomina Embryologica Committee many years ago as totally unscientific and misleading because the embryo itself begins to exist at fertilization. All human embryology textbooks agree with that. My concern is with your statement that the embryo “begins at the end of the process of fertilization” with the formation of the “zygote”, as that is scientifically incorrect and contradicts the international nomenclature, as well as the Carnegie Stages of Early Human Embryonic Development (available online at: http://nmhm.washingtondc.museum/collections/hdac/stage1.pdf). The Carnegie Stages (23 of them) were founded in 1942 (not new!), and built on the scientific facts documented as early as 1883 with Wilhem His’s 3-volume tome on human embryology. Thus we have known for over a hundred years now that human beings begin to exist “at fertilization” – meaning, at the beginning of the process of fertilization. Quoting directly from the international Carnegie Stages:
“"Embryonic life commences with fertilization, and hence the beginning of that process may be taken as 'the point de depart' of stage 1. ... Fertilization, which normally takes place in the uterine (fallopian) tube, is the procession of events that begins when a spermatozoon mature sperm makes contact with an oocyte and ends with the intermingling of maternal- and paternal-derived chromosomes at metaphase of the first mitotic (cell) division of the zygote. Stage One of the embryo thus includes: (a) the penetrated oocyte - the term used once a haploid spermatozoon has penetrated the diploid oocyte (causing the diploid oocyte to half its number of chromosomes to 23) and, strictly, after the individual plasma membranes of the sperm and of the oocyte have become one; (b) the ootid, characterized by the presence of the male and female haploid pronuclei (each pronuclei containing 23 chromosomes); and (c) the zygote, which characterizes the last phase of fertilization. " Thus the “zygote” phase during the process of fertilization is not when a human being begins to exist, but rather the “penetrated oocyte” phase is (formed at the beginning of the process of fertilization). True, some textbooks write less sophisticated accounts because they are written for students, and thus tend to generalize. But all professional human embryology textbooks are required to go by the Carnegie Stages, which are represented in those same texts by the use of numerical superscripts that correspond with the relevant Carnegie Stage. The reason this is important is that a great deal of unethical human cloning and human genetic engineering research is performed before the formation of the zygote – and thus is literally destructive human embryo research. Hope this helps.
Dr. Dianne N. Irving, M.A., Ph.D.
I have enjoyed the “comments” on this issue, and am encouraged to see so many people engaged in trying to sort out what’s what, especially the scientific facts. I am both a bench researcher and a philosopher/medical ethicist, and have been involved in these issues for about 20 years now. I can’t respond to each and every entry, but FYI I have noticed a few things that really can be cleared up rather easily, and have given the URLs for some of my articles that go into much more detail, with scientific references, than is possible here:
-- Reference has been made to Maureen Condic’s article (she is not a human embryologist), “When does human life begin”. However, although she provides several important empirical facts about the process of fertilization, there are serious scientific errors in her presentation, not the least of which is the fact that she contradicts herself numerous times by stating that the embryo begins when the sperm penetrates the oocyte and that the embryo begins with the formation of the zygote. As I have already commented (above), this blatantly contradicts the Carnegie Stages of Early Human Development. This and other scientific errors I have noted in my article, “Condic’s ‘Pre-Zygote’ Error in ‘When Does Human Life Begin?’”, at: http://www.lifeissues.net/writers/irv/irv_134maureencondic1.html
-- As for the comments about human embryologists O’Rahilly and Muller, their textbooks are probably the #1 acknowledged internationally. In fact, O’Rahilly has been on the international Nomina Embryologica Committee since its beginning many decades ago. The first to systematically study human embryos was Wilhelm His (Anatomie Menschlicher Embryonen 1880-1885, 3 vols.), and the first to stage them was Franklin Mall in 1914. Later George Streeter (Streeter 1942, p. 211; Streeter 1945, p. 27; Streeter 1948, p. 143) laid down the basis for the currently used Carnegie staging system, which was completed by Ronan O'Rahilly in 1973 and revised by O'Rahilly and Muller in 1987. The Carnegie Stages are often referred to as "the Bureau of Standards" of human embryology (O'Rahilly and Muller 2001, p. 3). Today they continue to be verified and documented by the international Terminologia Embryologica (formerly, Nomina Embryologica) committee, which consists of more than twenty experts academically credentialed specifically in human embryology from around the world. After reviewing the latest research studies in human embryology, their deliberations have been published in the international Nomina Embryologica, part of the larger Nomina Anatomica (now known as the Terminologia Embryologica, soon to be published as part of the larger Terminologia Anatomica). You can access the Carnegie Stages of Early Human Embryonic Development yourself at the National Museum of Health and Medicine:
http://nmhm.washingtondc.museum/collections/hdac/stage1.pdf
-- To state that there is “not a consensus on what an organism is” is factually wrong. Much of the strategy of those who want to perform research that is fundamentally unethical is to insist that “we just don’t know”, i.e., create a Doubt where none exists in order to confuse people. Another successful strategy is to try to convince people that the immediate product of both sexual and asexual human reproduction is “just a cell” – not an organism. The fact is that the immediate product of both sexual and asexual human reproduction is a single-cell human organism. For a brief discussion of the difference between an “organism” and a “cell”, see my article, with the scientific references: “Definitions of a “human organism” and a “human cell”, at: http://www.lifeissues.net/writers/irv/irv_78definitions.html
-- Scott Gilbert’s text is mentioned. Gilbert is a bioethicist, not a human embryologist, and his “textbook” is loaded with biased and erroneous “scientific facts”, including those concerning the early human embryo. Human embryologist Ward Kischer and others have attempted to contact him with the proper corrections, to no avail. His text is meant for non-scientists who would believe anything a bioethicist has to say.
-- The issue of “twinning” is a bit complicated, but has been explained in detail in human embryology and human molecular genetics textbooks for decades. One of every two human monozygotic twins is thus reproduced asexually, in naturally occurring twinning in vivo as well as artificial twinning in vitro. According to human molecular geneticists, twins are the most “identical” because they share both their nuclear and their mitochondrial DNA (yes, there are genes outside the cell nucleus!). Of note, politically, “twinning’ has been used in IVF and other ART facilities for decades now – both for “infertility treatments” and for pure research. It is variously referred to as “embryo multiplication”, “embryo splitting”, “blastomere separation”, etc. I have referenced several textbooks explaining the details of twinning in my article, “Playing God by manipulating man: Facts and frauds of human cloning”, at: http://www.lifeissues.net/writers/irv/irv_22manipulatingman1.html.
-- Finally, many people are still using the terms “fertilization” and “conception” to refer to when a human being begins to exist. This is not only scientifically erroneous, but also dangerous when such exclusionary terms are used in any legal documents. Many don’t realize that formal definitions in a bill, regulation or law are very specific and narrowly defined. Thus, if a scientific term is mis-defined, or even left out, then the legal document would not apply to all other cases. For example, there are many different kinds of human cloning, but if a law defines “cloning” only in terms of somatic cell nuclear transfer (SCNT), then it would not cover all other kinds of cloning – and thus “allow” it by default (called a legal loophole!).
The reason why the use of the terms “fertilization” and “conception” are very problematic in these debates is that not all human beings are reproduced by sexual reproduction (fertilization); many are reproduced by asexual reproduction (natural and artificially reproduced human monozygotic twins, human genetic engineering, etc.). Therefore, to claim that all human beings are reproduced at fertilization is to leave out the millions of human beings who are reproduced asexually. The term “conception” is also for that reason similarly problematic, but perhaps worse since the term is already defined as ‘beginning at implantation” in many state laws. Worse, if the term “womb” is used, that term would not cover the earliest human embryo already existing in the woman’s Fallopian tube trying to move to her uterus. For a more detailed discussion of this, see my article, “Neither, Nor: Bryne's and Willke's Pseudo-Battle Over Human Embryonic Stem Cells” (June 19, 2008), at: http://www.lifeissues.net/writers/irv/irv_129bryneandwillke.html.
Hope this helps.
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