The Carnegie Stages

Judie Brown’s commentary entitled “Caylee Anthony” contains a scientific error that should be corrected. In that commentary Brown writes, “This may sound callous to those people who do not equate a preborn baby—zygote, embryo, and fetus—with someone as adorable as a three-year-old child.” 

The problem exists in the use of the phrase “zygote, embryo, and fetus.”

Upon further study and consultation with those who understand human embryology far better than I do, it is clear that accurate language demands that we set the record straight so that “Caylee Anthony” reflects what the Carnegie stages—to which I referred—actually tell us about the human being.  

1. The “zygote” is NOT when a new human being begins to exist. According to the Carnegie stages, the “zygote” is at the “phase” of development during Stage 1 that is formed at the end of the process of fertilization, referred to as Stage 1c. Before that, the human embryo already exists at Carnegie stages 1a and 1b. According to the Carnegie stages, the new sexually reproduced human embryo begins to exist at the beginning of the process of fertilization, at “first contact” and fusion of the sperm and the oocyte (Stage 1a), then develops to the “ootid” phase (Stage 1b). Only after that does he/she continue to develop further to the “zygote” phase (Stage 1c) at the end of the process of fertilization. 

2. Most asexually reproduced monozygotic twins begin to exist as multi-celled embryos and therefore never do go through a “zygote” phase. 

3. By using the term “zygote” as the beginning of when all human preborn children begin to exist, I inadvertently left out all of those asexually reproduced monozygotic twins, as well as all human embryos already existing at Stage 1a and Stage 1b, whether sexually or asexually reproduced. All of these human embryos also just happen to be at the stage of development that is desired by researchers and clinicians of genetic engineering—for pure destructive research, as well as for reproductive (“infertility treatments”) purposes. It is also when huge quantities of human embryonic “biological materials” can be produced commercially for massive use in the in vitro production of human embryonic and stem cell culture media and genes and for the “controls” required for growing human embryos and human embryonic stem cells in any kinds of cell cultures. (The biochemical “conditions” and “environments” that are required for normal human cell, embryo, and fetal growth and development are likewise required for those processed artificially in laboratory conditions!)

4. It would have been totally accurate if I had written, “This may sound callous to those people who do not equate a preborn baby—from the beginning of his/her biological development as a human organism—with someone as adorable as a three-year-old child.”

5. Further, by writing “zygote” first, followed by “embryo,” I implied that the zygote is not an embryo and this is a false statement.

6. Finally it should be noted that the term “human embryo” scientifically refers not just to the single-celled human organism, but also to the developing embryo through eight weeks of development (the “embryonic period”). The “fetal period” of development does not begin until the beginning of 9th week. This is true whether sexually or asexually reproduced, whether in vivo or in vitro. 

It is imperative that we do all within our power to use accurate language, and that when we fail to do so we correct the record for the sake of those who must articulate the accurate science properly.

Terminology review:

Fertilization: For the sexually reproduced human being, there are three stages to the fertilization process, and the end result is the human zygote.

Asexual reproduction: This refers to all those individual human beings who come into existence without the sexual process known as fertilization.

In vivo: occurring within the mother; a natural process

In vitro: within glass, such as in vitro fertilization

If you have any questions, please do not hesitate to contact American Life League. As we so frequently say, human lives are at stake.