I was recently involved in a strange Twitter debate with an abortion supporter who argued that the fetus was a part of the mother. I suppose this was based on the silly “my body, my choice” mantra, but it surprised me that someone would actually consider that slogan a serious reason, particularly in this age of increasing medical knowledge. But despite all evidence to the contrary, she insisted on believing that abortion was a matter of “healthcare” for the mother because the mother was the only individual involved since the fetus was a part of her body. Abortion supporters have even tried saying that the baby was part of the mother’s body because of the umbilical cord (which only connects the two together to provide nourishment to the baby’s separate body). Sadly, this level of scientific ignorance is rampant in our culture, so let’s see what medical experts have to say. And, as always, don’t just take my word for it; do the research for yourself. Now, let’s get to work.
“In biology and in medicine, it is an accepted fact that the life of any individual organism reproducing by sexual reproduction begins at conception, or fertilization.” – Dr. Micheline M. Matthew-Roth, Harvard Medical School’s Department of Medicine, speaking before US Congressional hearings on April 23rd, 1981.
“Now we can say, unequivocally, that the question of when life begins is no longer a question for theological or philosophical dispute. It is an established scientific fact. Theologians and philosophers may go on to debate the meaning of life or the purpose of life, but it is an established fact that all life, including human life, begins at the moment of conception.” – Dr. Hymie Gordon, Chairman of the Department of Genetics at Mayo Clinic in Rochester, Minnesota, at the 1981 Congressional hearings.
Harvard Medical School and the Mayo Clinic aren’t exactly no-name outfits, but maybe those were simply the isolated opinions of those two people. Maybe we’ve learned more about embryology since 1981. Maybe some embryology textbooks – particularly ones written since that time – could shed better light on the matter.
Ronan O’Rahilly and Fabiola Müller have this to say in their text, Human Embryology & Teratology:
“Although life is a continuous process, fertilization (which, incidentally, is not a “moment”) is a critical landmark because, under ordinary circumstances, a new, genetically distinct human organism is formed when the chromosomes of the male and female pronuclei blend in the oocyte.”
“The combination of 23 chromosomes present in each pronucleus results in 46 chromosomes in the zygote. Thus the diploid number is restored and the embryonic genome is formed. The embryo now exists as a genetic unity.” 
Drs. Keith L. Moore, T.V.N. Persaud, and Mark G. Torchia, confirm this distinction in their text, The Developing Human: Clinically Oriented Embryology:
“Human development begins at fertilization when a sperm fuses with an oocyte to form a single cell, the zygote. This highly specialized, totipotent cell (capable of giving rise to any cell type) marks the beginning of each of us as a unique individual.” 
“The zygote is genetically unique because half of its chromosomes came from the mother and half from the father. The zygote contains a new combination of chromosomes that is different from those in the cells of either of the parents.”
Bruce Carlson notes in his text, Human Embryology & Developmental Biology,  that fertilization ties up many “biological loose ends”, including the following:
- “It restores to the zygote the normal diploid number of chromosomes (46 in humans).”
- “The genetic sex of the future embryo is determined.”
- “Through the mingling of maternal and paternal chromosomes, the zygote is a genetically unique product of chromosomal reassortment, which is important for the viability of any species.”
T.W. Sadler, in Langman’s Medical Embryology, likewise notes the main results of fertilization as:
- “Restoration of the diploid number of chromosomes, half from the father and half from the mother. Hence, the zygote contains a new combination of chromosomes different from both parents.
- Determination of the sex of the new individual.” 
Finally, O’Rahilly and Müller seek to standardize terms in their profession and proceed to list 5 reasons why they do not use the term “pre-embryo”. Besides their point that “embryo” is already recognized as encompassing the point from fertilization to the 8th week, and there is no unified entity before fertilization, they state the following:
“It [the term “pre-embryo”] is equivocal because it may convey the erroneous idea that a new human organism is formed at only some considerable time after fertilization”
“My body, my choice” may make for a succinct slogan for pro-abortion signs and chants, but one thing should be readily apparent by this point: it goes against all we’ve observed about human development and is one of the most tragic anti-science stances a person can take. Whether you call it a fetus or embryo (they’re just different stages of development), the developing baby, from it’s earliest existence, is a unique human individual, and is never a part of its mother’s body. If abortion supporters want to argue their case for when it’s acceptable to take said baby’s life, then fine – let’s work through those reasons – but can we at least finally put to rest that tired old excuse of the baby being part of the mother’s body?
 Ronan O’Rahilly & Fabiola Müller, Human Embryology & Teratology, 3rd Ed (NY:Wiley-Liss, 2001), p. 33.
 Keith L. Moore, T.V.N. Persaud, Mark G. Torchia, The Developing Human: Clinically Oriented Embryology, 10th Ed (Philadelphia: Elsevier, 2016), p. 11.
 ibid., p29.
 Bruce M Carlson, Human Embryology & Developmental Biology, 4th Ed (Philadelphia: Mosby Elsevier, 2009), p. .
 T.W. Sadler, Langman’s Medical Embryology, 11th Ed. (Philadelphia: Lippincott Williams & Wilkin, 2010), p. 39.
O’Rahilly & Müller, p.88.