To the Committee of Health, Education, Labor, and Pensions
January 19, 2007

Stem cells come in many varieties. Even the term “stem cell” is a very general term. It defines a generic category of cells that has many members with different properties. It’s about as specific as the category “seed.” Seeds of all types share many properties, but an apple seed makes apple trees and an orange seed makes oranges. When we compare apples and oranges no one confuses the two.

After many years of competing claims, ES cells remain the most versatile of all stem cells. ES cells are the gold standard for the biological concept of pluripotency, and it has been known from over 20 years of research in the mouse that ES cells can make all the cells of the body. ES cells have unique properties and they fulfill a unique purpose in biological research. Human ES cells are irreplaceable tools for understanding the earliest stages of human development. They are unique precisely because they come from the earliest human embryos — before implantation into the womb, before even the most rudimentary human form has begun to take shape. Understanding how these primitive cells orchestrate the process of human development represents one of the greatest goals of modern biology.

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