The Arab proverb in the chapter title offers a concise yet profound statement on the current state of stem cell research. Despite many years of heated social and religious debates over the use of human embryos in embryonic stem cell research, it remains an undeniable fact that the caravan of stem cell science is proceeding at an unrelenting pace around the world. This situation is fascinating in and of itself. On one interpretation, the proverb may represent a fatalistic stance toward stem cell research, where progress in this direction is nothing but an inevitable stage within a naturally unfolding history of science. Or one may interpret it as suggesting the opposite point: that people’s economic interests have driven permissive social and scientific ideologies that feed and are conducive to those very same interests.

There is a grain of truth in each of these extreme views. In spite of much controversy, stem cell research continues to advance for several reasons. First, the term stem cell research encompasses a very wide range of scientific activity related to many different cell types: multipotent (adult) stem cells; embryonic stem cells and their direct derivatives; and somatic (body) cells that have been bioengineered to take on the pluripotent properties of embryonic stem cells – that is, their capacity to become any type of cell in the human body. Thus the caravan of stem cell science is composed of many parts and, as I argue in Chapter 2, it must progress together as a whole. Second, stem cell science – especially pluripotent stem cell research – has proven to be of high scientific interest, unfolding previously inaccessible mysteries about human development, genetics, degenerative diseases, and tissue regeneration.