Nadia Rosenthal, senior scientist at the European Molecular Biology Laboratory, discusses newly emerging discoveries that may indicate just how flexible adult stem cells may be in their ability to produce divergent cells in the body. Unlike animals such as sea stars, humans have a more limited ability to regenerate parts of the body but newly emerging research may help solve the evolutionary puzzle of why mammals have such limited powers of regeneration.

An adult stem cell is thought to be an undifferentiated cell, found among differentiated cells in a tissue or organ that can renew itself and can differentiate to yield some or all of the major specialized cell types of the tissue or organ. The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found.

Scientists also use the term somatic stem cell instead of adult stem cell, where somatic refers to cells of the body (not the germ cells, sperm or eggs). Unlike embryonic stem cells, which are defined by their origin (cells from the preimplantation-stage embryo), the origin of adult stem cells in some mature tissues is still under investigation.