Biology and Abortion

I have a couple of biology questions relevant to abortion.

My first question is about twins. One medical website says:

"*Identical twins start out from a single fertilized egg cell, or zygote, which is why they’re also called monozygotic twins. Like the single baby we just saw, the egg is fertilized by a single sperm cell.

Unlike the single baby, this fertilized egg cell will split into two separate embryos, and grow into identical twins. This remarkable event takes place during the first week after fertilization*"

How does this fit with the Catholic view that there is a new and distinct human being from the moment of conception (fertilization)? Do we really believe that in the case of twins a distinct human being splits in half and becomes two new human beings? I’m confused.

My second question is about what it is on a biological level that makes something a human being. As pro-lifers we make the point that an embryo has all the genetic makeup of a human being. It has human DNA and all the genetic information it needs to develop into an adult human being. But what about if, say, someone loses a limb? Or even just some dandruff? Biologically speaking, does the sundered limb or the lost dandruff contain human DNA and complete genetic information just like an embryo? Or is there a genetic difference? I feel that as pro-lifers we should be able to give a scientific explanation of what a human being is, hence my asking this question.

Thank you! :slight_smile:

The answers to metaphysical questions will not be found in the field of biology (or chemistry, or physics or any other natural science).

I second what the poster above me stated, about how some of these questions are about deeper matters than biology can answer.

Nevertheless, biology can help. Re: twins, in prolife apologetics circles I have heard people explain that a new and distinct human life comes into existence at twinning just as it does at conception. This is partly because an embryo’s small size makes it capable of doing things that we are not capable of doing later. Twinning is one of those things: when an embryo becomes twins, a distinct embryo comes into existence by splitting off from another, which is only possible when we are embryos. Also consider the ability embryos have of surviving in a cryogenic freeze. Later in life, we can’t do that, but God has deigned to create embryos that are so small that they (at first) have the abilities of individual cells.

Re: getting your arm cut off, the cells in your arm aren’t in the same situation as a single-celled embryo. By the time your arm is made, your cells have specialized by turning off various genes and turning on others. It is my understanding that only a cell in its embryonic state can grow a whole body. (Well, except for itself.)

Trent Horn answers the arm objection in one of his blog posts. Here is an excerpt:

“Some critics [say]…Yes, the fetus is alive and human, but every cell in my body is alive and human. Is every cell in my body a human being? … [T]his false argument confuses parts and wholes. Saying, ‘A fetus is alive and human. Sperm and egg are alive and human. Therefore, a fetus is a body part like sperm and egg’ is as fallacious as saying, ‘A truck is made of metal. Nuts and bolts are made of metal. Therefore a truck is a car part like a nut or a bolt.’ Because two things have traits in common does not mean they are the same kind of thing. Sperm, egg, and other body cells are parts of a human body. In contrast, a fetus, embryo, or even a one celled zygote that exists after conception is a whole human body that is able to develop itself over time.”

He continues: “The unborn are not mere tissue or body parts like sperm, egg, or skin cells. They are also not like cancerous tumors that can grow and even sprout body parts such as hair or teeth but have no potential to develop into an adult human. Instead, an unborn child, when given time, nutrition, and a proper environment (i.e., not outside the uterus) will develop into a mature human being if he does not die prematurely, which is not true of sperm, egg, or body cells.”

Senator Rubio is Right – Human Life Does Begin at Conception

I hope that helps. Please let me know. God bless!

I think we complicate this issue with too many words that most people are unfamiliar with. It is really very simple in my view. I read the following on the catholic answers website, I don’t remember the author but what was stated was simple and true. It goes like this:

If it’s growing, isn’t it alive.
If it has human parents is it not human.
And human beings like you and me are valuable aren’t we?

All true and very simple.:thumbsup:

I agree that this is complicating.things.more than what they are. As to twins if.we.go by the OP`s theory that the twins.become.two.separate persons after the separation then how do you explain that.conjoined twins are two separate persons? Obviously conjoined twins have two separate souls.despite the fact that they didn’t separate. Obviously then it is not one.soul in the beginning. Most likely the enrollment of.both twins happen at the beginning. is human, if it has 46.chromosomes,.two human parents, eats,.grows, is alive, then is human.

There is not much of a genetic difference, but it’s not all about genetic information. What makes the embryo important is the part it plays in creating a living person. You might say it has the potential to do so, naturally, whereas a scrap of human tissue does not.

Twins, whether identical or fraternal, are unique, distinct individuals from the moment life begins. They don’t share a soul. They have unique finger prints. They don’t share thoughts or dreams. They are truly different people.

Thank you all for your insights! And thank you in particular, dmar198, for your in-depth explanation! I’ll be sure to look into the work of Trent Horn in more detail as well.

For the second point, DNA is only one characteristic of life. There are seven, and zygotes, embryos, fetuses, and newborns meet all seven of those characteristics.

As do all other somatic cells including the cells of an amputated limb mentioned in the OP’s example. Appealing to the emergent properties of life to demonstrate personhood runs into the exact same problems as appeals to the unique DNA sequences of embryos.

Amputated Limbs don’t grow, nor do they adapt to their environment, nor do they take in energy for maintenance.

But the cells constituting a recently amputated limb do. They meet all seven of the emergent properties of life. They continue reproducing, metabolizing, responding to stimuli, etc. They are living cells, and that’s all the emergent properties were designed to qualify: whether something is alive. Meeting all of the emergent properties of life does not establish whether something satisfies the philosophical definition of a person.

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