The entire pro life movement is based upon the false idea that “life at conception” can be proved and is true. The fact is that it is impossible to prove that a life exists until birth.
Why? Because until the DNA of the genotype expresses the correct phenotype, one cannot tell if the product of conception is alive or is comprised of enough human DNA to live as a human. The “genotype” is the “code” or “plan” that is used to build a human and to say that it must “express” simply means that it must build a structure or “phenotype” based upon the DNA. The DNA of the genotype is quite complex and must go through a process of its own. The DNA must produce RNA that then must produce the phenotype in the form of structures comprised of proteins or other necessary products such as enzymes. All of the parts of the human body are the phenotypes of human life. http://en.wikibooks.org/wiki/Cell_Biology/Genes/Gene_expression
Some say that because the DNA of the sperm fuses with the DNA of the egg, that is proof that a human life has been created. The problem with that idea is that most zygotes do not produce human life. Most die in the first trimester. Some say that there is “life at conception” because the DNA of the egg and sperm fuse at that point and that it is therefore the first instance of a new human life. While it is in fact one of the stages of human life it is not the first. In fact the first stage of human life was the stage that created the first human and the last stage will be the stage that produces the last living human. All other stages are intermediate. For example if the claim is that the zygote is an earlier stage of a baby and is therefore the same as a baby, then the gametes are an earlier stage of the baby as well. If the zygote is a baby, then the sperm is a baby and the cell in meiosis is also a baby and so on all the way back to the first human.
It is a fact that until the DNA of the genotype expresses the correct phenotype we cannot tell if the product of conception is alive or human. Why can’t we tell if the phenotype is human or not human enough to live as a human? The main reason is that there is no accessible means to tell if the DNA will in fact express the correct phenotype or if the phenotype is alive at any instant or if it is capable of living until birth. For example there is no “green light” we can view that says everything is “OK” and this is a human or this is alive. There is not even a “yellow light” or “red light” that says caution or stop, this is dead. One cannot even do genetic testing to tell if the fetus is alive or comprised of foolproof DNA because the DNA must “replicate”, not once, but billions of times before there is a birth. And each of the replications will produce DNA that may or may not yield a different “expression” of the parent DNA. For example the DNA of the zygote will divide and produce essentially the same DNA as its parent, either copy can produce an entire baby such that we may have twins, triplets or other multiple births. Or the zygote can simply progress to the next stage and produce a single child. http://en.wikipedia.org/wiki/Human_genetic_variation There is no “indicator light” that tells in advance that this zygote will produce twins or simply a single child. And past that stage, the DNA produces other DNA billions of times and each copy of the DNA can have a different “expression” of its code than the DNA of the parent. For example the early DNA can produce different parts of the body or different proteins or enzymes despite the fact that the outward structure of the DNA and chromosomes will appear to not have changed. None of the DNA has a switch or indicator or any outward sign that says this will produce a living human baby that will live until birth.
Of course we can look at sonograms, or genetic test and determine if things “might” be compatible with life. For example we can look at a sonogram and see what appears to be a healthy living baby. However, many of those babies will in fact die before birth. There is no “green light” showing that a fetus is perfect and can live to birth. And because many do not live, we cannot assume that they will all live. In fact we must assume that most zygotes will not live.
The possible reasons that a fetus cannot live are numerous. For example there are several processes that must occur before birth. The fetal heart, that is different from the heart of a born baby, must change its blood flow pattern by the closing of valves. If the valves are not genetically perfect, then the fetus may die. The fetus must change its respiration from using the oxygen of the mother to using its own lungs. If that process has genetic flaws then the fetus may die. The fetus must change its digestive process and if that process is genetically flawed it may die. So there are numerous reasons that genetic testing and sonograms cannot show the status of the life of a fetus. A fetus could appear to be healthy and in fact only have seconds to live.
This is not to say that genetic tests and sonograms and other processes will not indicate that there is “life”, it simply means that there is no test that the life is sufficiently human that it will live to birth. And test may not be able to prove that the life will live, but the tests can prove that the fetus is dying or dead and will not live to birth. For example tests can show that the number of chromosomes is incorrect and will not produce a living baby even though it is alive at the time of the test. And tests can show that the fetus will not live past a certain time outside the womb. Further, genetic testing can show that the fetus is comprised of the correct genetic materials but still does not have a chance of living due to other problems. http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20100/Bio%20100%20Lectures/genetics-%20human%20genetics/human.htm
These precepts are born out in the record of miscarriages that occur in nature. In the first trimester 70 percent of conceptions die with 60 percent of those conceptions dying of genetic flaw. Of those surviving another 15% will die before birth. And of those that do make it to birth, another 1 percent will die. Then shortly after birth another percentage will die of undetected genetic flaw or disease. http://www.med.yale.edu/obgyn/kliman/placenta/articles/UpToDate.html
In conclusion, there is no “green light” or indicator of any type that is possible with any phenotype that must replicate its DNA billions of times without a flaw. And because DNA can “express” different phenotypes at different stages of life, one cannot tell if the DNA will produce the correct phenotype the next time it replicates. So even though the DNA looks sufficient in the first copying of the genetic code, it may not be sufficient in a following copy of the code. The point being that by looking at an earlier copy of the DNA code, one cannot tell what a future copy a billion copies later will produce. There is just no way to prove that a human life is living at conception, will live to birth or if the zygote will produce a DNA code that is compatible with human life that can live as a human.