Wherein I clear up some misunderstandings about human taxonomy

I pointed out yesterday that it is a scientific fact that a zygote/embryo/fetus is a human being. There is no debate about the science. There is a debate about ethics-- at what point do human beings acquire the right to life ?-- but there is no scientific debate about the fact that a zygote is a human being.

Some of our commentors said things that suggest that they misunderstand the science. I can help educate them:

Commentor WR:

No. A fertilized human ovum is human, but it's not a human being, it's not a person. It has to develop to a minimum stage before it can be called a person. I personally would put that at no earlier than 24 weeks gestation, the earliest date that the fetal nervous system has developed anywhere near enough to be able to feel pain. Even then, it's still not viable enough to survive outside the uterus.

WR mentions three predicates-- human, human being, and person.

Human means relating to a member of our species. A skin cell from Cher is human. A human skin cell. But the skin cell is not a human being. Cher is a human being.

Human being means a living Homo sapiens. A zygote is a living Homo sapiens. It is what a living human being looks like at one minute of gestation. Terri Schiavo was a human being (before they starved her). She was a human being at conception, at birth, during childhood and adulthood, and after her brain damage. In classical terms, she was substantially a human being at every point from conception to death. Her accidents changed-- her size, intelligence, appearance, abilities, etc.

Persons are entities with rights under law. Most persons are human beings, although some laws endow corporations with personhood, and some animal rights advocates suggest that some animals be legally called persons.

The debate about abortion centers on the concept of persons. Are all human beings persons? Do all persons have a right to life? These are the questions that matter. Obviously abortion fans are uncomfortable with these real issues, and prefer to skew simple biology in order to confuse the debate. We must not let them.

Comentor anonymous:

So a zygote is a unicellular human being? And sometimes, after a few rounds of cell divisions, it becomes two human beings (monozygotic twins)? Does Jesus insert a second soul at that point or does the original soul divide into two? Is it a double murder to abort a zygote that is about to split?

A zygote is a human being. Sometimes it is more than one human being. It is never less than one human being.

I have no insight into the theological mechanics of twinning.

Commentor Anonymous:

So a zygote is a unicellular human being? Does it have a soul? And if it splits into two, a few rounds of cell divisions later, which of the twins gets the original soul?

A soul is the substantial form of a living thing. A soul isn't a spooky apparition. It's just the intelligible principle of a living thing. A zygote has a soul. When it twins, each twin has a soul (a substantial form). The zygote has undergone substantial change, so neither soul is identical to the original.


Commentor KW:

Early in their existence both the rat and human embryos undergo incredibly similar developmental processes. The development of features in both embryos at early stages is controlled by the same Hox genes expressed in virtually the same ways. These early embryos are indistinguishable without special equipment and training. The gene expressions that result in virtually all the differences between rats and humans come latter in gestation.

The embryos are quite distinguishable, even by rank amateurs. Here's how: rat embryos grow into rats, and human embryos grow into humans.

That's the salient fact. Morphological similarities are irrelevant to what embryos actually are. Rat embryos develop into rat adults. Human embryos develop into human adults. Always. They never switch. Just like mom's uterine tissue clump never magically switches into a new human being at 20 weeks of gestation.

Each embryo is what it is from the moment of conception. Rat embryos are very young rats. Human embryos are very young humans.

Biology 101, KW. You should have stayed awake in high school.

KW:

I find it creepy and morbid that Christians would invest so much energy and passion fighting for the “rights” of an embryo that developmentally, morphologically, and functionally is virtually no different than any other mammal embryo.

We are fighting to protect human life.

I acknowledge that the fetus develops more human fetures all the time, and I would be happy to embrace a grand compromise that bans abortion after an agreed-upon stage of development (18 -20 weeks?), if anti abortion forces would cease there assault on early abortions and stop opposing birth control. Of course Christians and their Muslin allies will never go for that.

We are fighting to protect human life. We will never accept an "achievement test" to define human beings. Human beings have rights based on who we are, not on what we can do. We are all human at conception, and remain so until death. All human beings have a right to life.

Anonymous:

Its interesting that you take Myers' to task over his comments, but you don't actually bother to respond to his question. Specifically: "[W]hat are these “scientific qualifications”? List them, please." 

I suspect that you didn't because you cannot. And knowing that, you choose to obscure the issue by throwing up a pile of meaningless word salad instead.

The scientific qualifications by which a human zygote is a human being elude Myers, who is the only scientist in human history to be confused on this count.

Let me help. The qualification by which a human zygote is a human being is because nothing in biology makes sense if it is not.


Biological science depends on a coherent understanding of taxonomy, reproductive biology, genetics, evolutionary science, etc.

If human zygotes are not human beings, then a piece of tissue (what is it?) miraculously transmogrifies into a human being at 20 weeks or whatever for no apparent reason. Did it change species? Do human beings bud spontaneously from the uterine lining of females? Did the DNA suddenly mutate from 'blob DNA' to 'baby DNA'? What is the biochemical basis for the sudden speciation at 20 weeks? What is the physiological basis for the transition from abortionist cash-cow to mama's little prince/princess?

Do explain the science. Please. 

KW:

Dr, seriously, humor me here. What if instead of Terri Schiavo having a liquefied brain, her entire head was lost in an accident and her body from the neck down was being kept alive with advanced medical technology, would that body be a human being? Would there be any point in keeping it alive? I don’t think so. What do you think? Might the soul still be in there? 

Schiavo didn't have a "liquified brain". She was a handicapped person with brain damage. Much of her brain worked reasonably well. She needed care, of the sort a young child needs. She was handicapped. She lacked substantial intellectual capacity and motor control. She was not brain dead, or even close.

If she were decapitated and her body below the neck maintained artificially, it would be similar to a kidney that has been removed for transplant that is kept mechanically perfused until it is transplanted. The decapitated body and the kidney are human, in the sense that they are parts of human beings, but they are not human beings.

Keep the comments coming. This is fun!