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Jack Sisson's Life Ethics Blog

We must find new ways through many ethical issues, especially regarding bioethics, medical ethics, and criminal justice. Jack Sisson's 'Life Ethics' blog focuses on numerous areas of concern, including the philosophical and ethical dilemmas surrounding stem-cell research, abortion, medical research, and health care.

What do we make of those rare instances in which two non-identical twin embryos merge into one? The resulting chimera can contain different sets of chromosomes from four gametes -- two eggs and two sperm. This anomaly can cause faulty DNA testing (especially if the merged embryos were the same sex), because most of the body may contain one set of chromosomes, while the other set may be found in only one or two organs.

This is what happened to Lydia Fairchild, who had to go to court to keep her children after DNA testing showed they weren't hers. It wasn't until doctors took a cervical smear that they discovered Lydia was a chimera with 2 separate female DNA strands. Because DNA testing is relatively new, and also because it's not usual for people to have their DNA tested, same-sex chimeras may be more numerous than previously believed. Unless they develop an abnormality like skin discoloration or different eye colors, same-sex chimeras look perfectly normal.

It's easier to determine chimerism if the merging embryos are different sexes because genitals of both sexes are formed. Sometimes one sex is dominant, like the newborn who appeared to be male, but was found to have an ovary and a fallopian tube.

So why this discussion of chimeras? Well, for one thing, if the original two embryos were destined to become certain unique individuals, this merge could not happen, especially since embryos of opposite sex can merge. Were the multiple embryos destined to become a single embryo all along? If so, which set of chromosomes determined the merge?

If human life begins at conception, then how many souls does a chimera possess? Let's reverse the questions I posed about twinning: if a zygote is destined to merge with another zygote, does each of the original fertilized eggs possess a soul? Further, does the chimera contain one soul or two? We cannot argue that one twin dies, because the resulting embryo contains DNA from two distinct embryos.

Until it is determined that an embryo is going to develop into a single unique human being, how can we invest it with personhood? As I've repeatedly said, at the blastocyst stage, when stem cells are taken for research, the embryo is not guaranteed to become a person. It can spontaneously abort (as do half or more), it can split into two or three individual embryos, or it can merge with another embryo to form one.

Ignoring the realities and anomalies of science does not make them go away. Refusing to ask tough questions because they do not support one's preferred belief is hardly ground for a sound argument. It may be comforting to believe something "just because," but that does not make that belief true. When human life begins is a very tough question. Simple assertions of belief are easy. Searching for the truth is not.

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Moral Monkey?
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