We hear a lot about "stem cells," which are front-and-center as a major policy debate in America, one that involves science, medicine, ethics, politics, and much more.

What are the issues? What's at stake? What are embryonic and non-embryonic stem cells? What are the crucial differences and distinctions we need to make as a society and citizenry?

Stem-cell technologies are some of the newest and fastest developing biotechnologies. Typically, along with genetic engineering and cloning, these technologies constitute the kind of 21st century advances that make this “the century of Biology.”

A stem cell is a type of cell that is nonspecific in its function; in contrast, for instance, to a heart or brain cell, which is functionally specific. There are two major sources of stem cells: embryonic stem cells and non-embryonic stem cells. Embryonic stem cells are obtained from 5- to 12-day old embryos. Although removal of a stem cell from an embryo kills the embryo, the stem cells are valued for their potential to produce any type of cell. That is, they have high plasticity. Conversely, non-embryonic stem cells are found in large quantities in placenta, umbilical cord blood, amniotic fluid, and in essentially all adult organs or tissues, including bone marrow, fat, kidney, liver, pancreases, intestines, breast, lung, etc. Any of these non-embryonic stem cells have ample plasticity and can give rise to nearly any type of cells, including heart, liver, lung, muscle, etc.

Thus, the heart of the stem-cell controversy centers on the aforementioned fact that the extraction of stem cells from 5- to 12-day embryos kills the embryo. But that's not the only issue: In addition, stem cells derived from an embryonic human may, in turn, reject the person who receives them. This situation is called graft-versus-host-disease (GVHD). The problem can be avoided by producing an embryonic clone of the person needing the stem cells. However, the procedure produces an embryo that is indistinguishable from an embryo from a fertilized egg. This embryonic clone would be destroyed during the stem-cell harvesting required by the therapy. This type of cloning is called "therapeutic cloning," since the production of a human baby is not the goal. (Reproductive cloning, producing a cloned human baby, has been universally outlawed.)

Another problem is that the embryonic stem cells can unpredictably cause cancer in the treated patient.