Development and Differentiation

The cells of most eukaryotes are of a variety of types and thus must undergo selective differentiation during development from the fertilized egg. This process has long fascinated scientists and philosophers but was buried in superstition until the 19th century. Then, the growth of embryology as a science led to the recognition that different kinds of cells exhibit distinct levels of potency for further differentiation in form and function. The levels range from many somatic cell, incapable of further development, to the fertilized egg, which can yield all cell types of the organism. Intermediate are the embryonic stem cells, which can be induced to produce a variety of cell types.