Stem cells are the primordial cells that allow a zygote to form into a human being or other animal. By maintaining viable stem cells into adulthood, some animals such as some lizards and the octopus are capable of regenerating body parts. They are nondescript cells that have the potential to grow to become, then reproduce any other cell in the human body. This has led stem cell research to become one of the most important scientific fields of discovery in human history.
Stem cells provide the nuclear structure and genetic information required to develop into skin or other organ cells. Properly coaxed, a host of stem cells can become a tendon, liver or even a heart. These living, breathing body parts are genetically identical to the original host, therefore having the necessary qualities to make transplant rejection a remnant of the past.
Stem cells exist naturally in placenta and are readily accessible through this means, but serious religious and philosophical objections have been raised in many countries regarding the process required to harvest them. New research has provided a far less invasive method, and recently they have been developed in the laboratory by transforming other bodily cells into stem cells.