Photo credits (top of page, left to
right): Human embryonic stem cell culture (University of Wisconsin-Madison,
News and updates, 2006), Embryonic stem cells (Biotechnology
Australia, 2006), Nerve cells that were differentiated from embryonic stem
cells (ALS Association, 2004), Neural stem cells (Orion Biosolutions, n.d.),
Scanning electron micrograph of an adult bone marrow stem cell (Basu, 2003)