Some have written that a human person does not begin at the time of conception when sperm and egg unite, but only sometime later. The reasons given:
1. The possibility of twinning is still present at the early stages of conception and development; it seems that we become human 14 days after conception, when the primitive streak appears and twinning is no longer possible.
2. The primordium of the cerebral cortex, of the specifically human brain, appears only later; that is when human life begins.
Response
The line of development is continuous from the one cell stage, through all intermediate development, until the child is born. Science can find no sign of change in the process of growth, of a switch from non-human to the human state. No scientist claims to see such a change.
If twinning occurs:
1) Either the original person remains without change and God creates a second person;
2) Or God created two persons in the first cell, who later separate into two bodies. Think of Siamese twins, two persons joined bodily.
3) or the first person dies (less likely); God then creates the twins.
Geneticist Jerome Lejeune, M.D. explains how development is a continuous process from fertilization until birth. The DNA contained in the 46 chromosomes of the fertilized first cell is the beginning of human life; the life force in living DNA directs development, giving the dynamism of life to the particles, atoms, and molecules which it animates. The body building materials are interchangeable, but the life message arranges them into one organic life:
A chromosome [coiled DNA] is very comparable to a mini-cassette, in which a symphony is written, the symphony of life. Now, exactly as if you buy a cartridge on which Eine Kleine Nachtmusikfrom Mozart has been registered, if you play it in a normal recorder, the musician would not be reproduced, the notes of music will not be reproduced; they are not there; what would be reproduced is the movement of air which transmits to you the genius of Mozart. It's exactly the same way that life is played. On the tiny mini-cassettes which are chromosomes are written various parts of the opus which is for a human symphony; and as soon as all the information necessary and sufficient to spell out the information necessary and sufficient to spell out the whole symphony is there, this symphony plays itself; that is, a new man is beginning his career (Testimony, August 10, 1989, before the Circuit Court for Blount County, Tennessee, printed by Michael J. Woodruff, Director, Center for Law and Religious Freedom, Annandale, Virginia; p. 4).
Lejeune explains that the initial cell divides into two about 20 hours after fertilization; after about another 20 hours one of the 2 divides again; now there are 3. That there are 3 at this stage is well known among geneticists, but why this should be is not certain. The still undivided cell may be the one which will form the placenta. One is tempted to suggest that the three cells, via biological communication, finalize their corporate individuality before proceeding to further development. This might also be the stage at which twinning occurs sometimes.
After the temporary pause at the 3 cell stage, the other first generation cell divides also; now there are 4; the 4 divide into 8, then into 16; at the 16 cell stage, possibly at the 32 cell stage, a compaction occurs; the 2 cells which had first divided, and possibly the split-off of the other first generation cell, are compacted inside the sphere, forming its center; these 3 build the body.
In the periphery around these 3 core cells are the 13 others; 7 are located in satellite or equatorial positions related to the 3 core cells; 3 others are located on top, and 3 on the bottom in the pole positions. These 7 + 3 + 3 build the placenta. Dr. Lejeune believes that if twinning occurs, one of the 3 core or somatic cells is involved, not one of the 13 which proceed to form the placenta; twinning will not occur beyond the 16 cell or the 32 cell stage. (Private conversation, Houston, April 14, 1993).
In 1987 the discovery was made that the DNA of an embryo at age 3 days, when there are 4 or 8 cells, can be identified. People working with in vitro fertilization were able to remove one cell by carefully puncturing the zona pellucida with a tiny hole, removing it, then closing the hole. The DNA of this cell was then reproduced via "chain polymerization" to make an analysis. Millions of copies of the DNA can be made within 24 hours for analysis. Only one single person in the world has the specific pattern of DNA which marks this individual: "The DNA specific to each person, after we have used the technique, will look like a little succession of strips - lines of various widths at various distances, giving a distinctive pattern for each human being. It looks very much like the bar-code that you are familiar with in the supermarket... a DNA code which is "absolutely specific to each of us." ("Genes and Human Life" in ALL AboutIssues, Fall 1991).
The parents of a child can also be ascertained by means of the DNA code: "If we compare the bar-code of a person to the barcodes of the father and mother, we can recognize that in all the lines which are specific to this person, half of those lines are found in father, half of them are found in mother ... We can know with less than one chance in 10 billion of error that this person is the biological descendant of this father and this mother" (Lejeune, Ibid.).
The fertilized ovum develops through the teamwork of the genes of both, father and mother. Two male nuclei inserted into an ovum from which the female nucleus was removed, do not build a human; what might happen is the production of a "molar degeneration" which can cause cancer. Neither can two female nuclei develop into a new human being. Without the male sperm, two nuclei in an ovum can become a dermoid cyst" but not a human being. Male and female genes must supplement each other. Dr. Lejeune explains:
Some of the bases of DNA carry an extra little piece we call a methyl, (CH3) which is hooked on it. This changes a bit the form of one of the bars of this long scale which is the DNA molecule... It is exactly comparable to what an intelligent reader (editor of a newspaper) does when he wants to underline with a pen some passage, or delete another. That is, with methylation, one gene is ... silenced, though it remains in place; but if it is demethylated at the next (cell) division, in the next cell it will speak again...
The DNA carried by the sperm is not underlined (or crossed out) by this methylation on the same places ... (as) the DNA carried by the ovum. During the manufacture of the sperm indications are given; these instructions are penciled in, so to speak. An "underlining" may give the order: "Do this, do that." But on the equivalent chromosome manufactured by the mother, the underlining is in a different place... Some information is to be read as coming from the male chromosome, and other information from a chromosome coming from the mother.. The fertilized ovum is the most specialized cell under the sun because it has built-in indications underlining segments of DNA which should be expressed, and others which should not be expressed; no other cell than just this one will ever have these same instructions in the life of this individual.
When one cell divides into two, we know that exchange of information passes from one cell to the other. When it is split in three it receives information that "we are an individual." And when it continues progressively, the underlining system is progressively changed so that cells differentiate; they specialize, doing a nail, doing hair, doing skin, doing neurons, doing everything... To summarize: If the message is a human message, the being is a human being (Testimony, p. 88; text slightly altered from original oral testimony).
I have made a table to illustrate for myself how the first cell divides into 2, then 3; then 4, 8, 16, and finally 32. [Table omitted here.]
The sketch is made to indicate that the first cell has the complete program for building the body and placenta. Each subsequent cell has the complete DNA materials of the original cell; but the DNA in the subsequent cells is marked with all that has taken place during the previous sequences of specialization, and instructions about what to do from here on. Each subsequent cell has its own marked DNA, specific to it alone. So a cell in the pupil of an eye which is blue, for example, has the same DNA materials as the first single cell; but a multitude of the DNA's sequences have already been spent and are therefore silenced in this end cell. This cell now knows only what remains to be done by itself; and can pass on sequential instructions to daughter cells when it replicates, either for replacement purposes or development.
Theoretically, if a way were found to reverse the instructions one by one, and to trace the sequences backwards one by one, it should be possible to track one's way through this maze back to the original fertilized ovum, the one in which the life began.
I marked the diagram to indicate that when a cell divides by mitosis, and instructs itself and the daughter cell, the mother cell remains in the mainstream of development whereas the daughter cell branches off into a side stream of specialization; but the mother cell will notch a mark on the DNA to note its progress along the mainstream. The 0.00 becomes a 0.000 in the mother cell, but an 0.001 in the daughter cell, for example. We might say that a 0.000 gene reserved its power to give sequential instructions along mainstream lines, whereas the 0.001 has instructions to innovate.
The illustration has limitations, but may be of some help to picture how we began. It is not a scientific theory proposed by geneticists, but a private endeavor to probe how life develops; how specialization occurs across a bridge of intermediate forms; how the entire body remains one united and living organism, and does not fall apart through mitosis and specialization; how sequenced DNA holds all the body together as one piece, like a team of acrobats who hold on to each other while performing feats on the high trapeze.
From the sketch we might coax the imagination to explain why our bodies reject foreign invaders like viruses and microbes, or implanted organs. The foreign DNA doesn't match with that of the home organism. The immuno-depressive white corpuscles make war on the invaders to keep this body as one codified unit.
Or, in the case of a conception, the new life is partially a foreigner to the mother; her body compromises; the new cell is barricaded within the protective zona pellucida at first, safe from marauding attack by white blood cells. The fact that the baby is not destroyed by the white corpuscles while it is tiny, while implanting itself in the uterus, indicates an armistice, probably because half of the DNA is from the mother. In general the baby keeps to itself and holds its own while sealed in its capsule in the uterus; the growing baby makes exchanges with the mother only via the fence or window of the placenta which is impermeable to marauding white corpuscles.
One reason why girls and women who have intercourse with multiple partners may develop cervical cancer, is the hostile reaction of their body to the foreign DNA of different kinds of sperm. But when couples are married, and do not use a condom, the mother's system appears to learn to tolerate this particular DNA of the sperm of her husband, which is always the same. And during the pregnancy with the first child, women whose husbands do not use a condom, have less trouble with eclampsia. The frequent contact of their bodies with the husband's DNA reduces hostile reaction against the baby which has partially the same DNA structure. But that is another question.
From what we have seen in the discussion above, science gives us no reason to believe that our human lives began in a colony of cells some days, weeks, or month after conception. On the contrary, science reveals that the life which is there later, is the one that began operating at the beginning, in the first cell.
Only God can know when He took the action of creating us; when He said: "Let us make THIS man in our image, in our likeness" (cf. Gen 1:26). Out of respect for God, and deference and gratitude to Him, we honor our own beginning which took place in His presence, by the might of His power. And we honor every other beginning of human life, never daring to kill the life which God has already created at the time when the first cell began a life of its own; or the life which He is now planning to create at the moment of His choice, which is not our choice.