Tuesday, March 23, 2010

Book study part two

Each Tuesday, we will be cross-posting Gerard Nadal's discussion of Embryo: A Defense of Human Life. Today is the second installment of eight.

There is no way for me to condense all of the biology that the authors present in Chapter 2, Fertilization. They discuss a great deal about which much has been written here. Click here for several lessons in mitosis, meiosis and fertilization. Apart from the recapitulation of the biological fundamentals, I wish to bring out of the chapter a few key points made by the authors.

First, the biology presented in the chapter is flawless! For any who would suggest that perhaps a couple of philosophers miss nuanced features of biology which might lead them into erroneous conclusions, let me state as a molecular biologist that this chapter could easily be mistaken to have been written by an embryologist.


Recalling that the sperm contains half the number of chromosomes and the egg the other half, these two haploid cells join to form a diploid cell, the zygote. A question arises asking when the zygote comes into being. Is it upon penetration of the egg by the sperm, or when the two gametic nuclei join to form a diploid nucleus? Some say the latter, but I tend to agree with the authors in claiming the former, since, as they rightly point out, that after penetration of the egg by the sperm, both gametes cease to be (both structurally and functionally) as they were before. They form a new entity, both structurally and functionally.

Both sperm and egg exist as such as parental tissue types. When joined, a new biological organism comes into existence, with its own unique genetic identity and intrinsically unfolding developmental trajectory.

Despite the slight differences of opinion, the authors note that, “…there is widespread agreement among embryologists both that a new human individual comes into existence when there is a single, unified, and self-integrated biological system, and that this happens no later than syngamy.” (Syngamy=The lining up of the 23 pairs of chromosomes.)

The authors then run us through the various stages of embryological development:

Zygote, cleavage, morula, blastula, gastrula, up to the formation of what is known as the primitive streak. Prior to this, the embryo is capable of twinning, an issue that will be dealt with substantially in chapter 6.

Twinning is an important issue in development, as some would posit that prior to this stage, an individual does not exist. However, the authors quote a number of embryology texts which mark fertilization, not gastrulation, as the beginning of a new human individual.

The events of development described by the authors can be viewed in both 4D sonograms and fiber-optic videography at The Endowment for Human Development.

The authors go on to make several points about the human embryo:

1. It is distinct from any maternal or paternal cell. It is growing and has its own distinct direction.

2. The embryo is human, with a genetic make-up characteristic of human beings.

3, The embryo is a complete or whole organism, though immature.

The bottom line: A human embryo is not something different in kind from a human being. A human embryo is a whole living member of the species Homo sapiens in the earliest stage of his/her natural development.

Are embryos produced by in vitro fertilization and cloning still human organisms?

The authors say ‘yes’.

For IVF embryos, they are the product of sperm and egg union in a Petri dish rather than a fallopian tube.

For cloned embryos, they are the result of an egg that has had its haploid nucleus replaced by a diploid nucleus from a diploid body cell. The resultant ‘clonote’ (as opposed to naturally occurring zygote) functions as any embryo. Because they are the same as any other embryo, they ought to enjoy the same moral worth as any embryo.

Those are the chapter highlights. Chris, if I missed anything, my apologies. It’s been a hectic day.

There’s the red meat of all pro-life argumenation.


No comments: