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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.

 
Twins have intrigued us since the legendary Romulus and Remus supposedly founded Rome. Stories of twins separated at birth living nearly identical lives; twins' secret languages; the sense of incompleteness that haunts a surviving twin, sometimes for life; all are part of the twins' mythology. In addition to their lore, twins also bring another component to the "beginning of human life" question.

In the past two decades, the number of multiple births in the United States has jumped dramatically. Between 1980 and 2000, the number of twin births has increased 74 percent, and the number of higher order multiples (triplets or more) has increased fivefold, according to the National Center for Health Statistics. Today, about 3 percent of babies in this country are born in sets of two, three or more, and about 95 percent of these multiple births are twins.
Read the entire article here.

Fraternal twins form when two fertilized eggs implant at the same time. (The eggs are fertilized by separate sperm.) Also known as dizygotic twins, they develop separately, with separate chorions and separate amnions , although they may share the same placenta. Genetically as different from each other as any other siblings, they can even have different fathers. Approximately 72% of twins born in the U.S. are dizygotic, and about 30% of them are of opposite sex .

Identical twins are, to me, a little more interesting. These twins, known as monozygotic, are much rarer than dizygotic twins; only 3-5 per 1000 are born worldwide. Monozygotic twins form when one sperm fertilizes one egg and then splits into two separate embryos. Why the zygote splits is a mystery, although there is speculation that “monozygotic twinning may be a teratologic event” Identical twins have the same DNA and can only be the same sex.

Monozygotic twinning presents a problem for those who believe that human life begins at conception. With identical twins, conception creates only one fertilized egg (zygote), a single human life for those who subscribe to this belief.

What does it mean, though, when that human life suddenly splits and forms another, genetically identical, “human life”? Did that human life begin at conception? And if theories linking monozygotic twinning to teratogens are true, then the second twin did not exist until the original zygote was affected by the teratogen. You might even call the second twin a chemically induced embryo, although technically, it is a clone.

To be continued


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