Last time, I gave an overview of the pro-life argument in Embryo. I'm not going to critically discuss most of what's in the book. Instead, I only want to explain a couple of major places where Embryo zigs and I zag.
To shorten things a bit, I'm just going to agree with the first step of George and Tollefsen's (G&T's) argument. Embryos are distinct human organisms. Done.
I can also almost agree with G&T's second step. I am a human organism, just as embryos are. Where I start to diverge is this notion that I have a definite "substance kind" independent of how the inquiry is framed.
When we speak of substance or nature or essence, we are drawing attention to the kind of thing an entity is and the various properties or characteristics that an entity might possess accidentally, contingently, or temporarily.1G&T then ask readers to consider an oak tree to understand that being an oak tree is its "substance or essence or nature." But what if they had asked readers to consider a tree to understand that being a tree is its essence? Now, if I point at something which is both a tree and an oak, is its substance kind tree or is it oak tree?
Tree. Then why not plant or living being?
Oak tree. Then why not quercus dumosa (one of many species of oak)?
Both. Then "the kind of thing an entity is" admits of multiple, compatible answers.
Perhaps the authors use "oak tree" for familiarity, but would have preferred a species name like quercus dumosa; they are trying to make a point about the species homo sapiens after all. Here's the catch: modern evolutionary theory undermines the idea of species as natural kinds. The concept of a species (like the concept of a language) is a convenient label for a cluster of organisms (or idiolects) that are significantly more similar to each other than another cluster of interest. I see no in-principle reason to stop at species when asking what "kind of thing an entity is," even if we're limiting our inquiry to genetics. My substance kind may as well be heterogametic human organism if we're having a discussion at that level.
What I'm saying here is that essence vs. accident is a matter of focus, not ontological fact. How does this affect the pro-life argumentation in Embryo? Let's look at two excerpts. The first is an explanation of why the essence vs. accident distinction must not be overlooked (let alone denied!):
Among the areas in which the gravity of this mistake is most clearly seen is in the area of embryo ethics. For embryos clearly cannot think, choose and speak; nor are they (yet) self-conscious or even sentient. Were this to mean that embryos were not the same kind of beings as the readers and authors of this book, that they were not persons, then it would be difficult to see why they should be accorded the same moral respect that we, authors and readers, believe we are entitled to.2The argument here needs a little more context before it becomes clear. We get a strong hint later in the chapter:
Body-self dualists look only at the properties essential to human life, such as mental functioning and self-consciousness, as they exist at the height of their development. But where could such properties come from if they were not already rooted in the nature of the being that possessed them?3So, roughly, the idea is that we adults can only derive our mental properties from our nature/substance kind. We only have one substance kind: human organism. Any moral respect due by virtue of possessing a property is due by virtue of membership in a substance kind with that property. Therefore, any moral respect due by virtue of our mental properties is due by virtue of being a human organism (which embryos also are).
But if substance kind is interest-relative, then the way the inquiry is framed can give the result of me having the same substance kind as an oak tree (both eukaryotic organisms), or a different substance kind from my mother (heterogametic organism vs. homogametic organism). We could even count "organism" as a substance kind if we are contrasting organisms against entities which aren't organisms.
Talking about kinds is useful in everyday speech, but I don't think such categories are as real as George and Tollefsen make them out to be.
1. George, R.P., Tollefsen, C. (2008). Embryo: A defense of human life. New York: Doubleday. p. 58
2. Ibid. p. 60
3. Ibid. p. 81