A difference in vision in cichlids in Lake Victoria could be pushing a species to split into two. (p. 14)

A new technique for converting adult cells to stem cells avoids dangerous mutations in cell DNA (p. 8)

Stem cells’ powers of self-renewal, immortality and potential for medicine inspire those who study them. But progress toward understanding them has been slow — it took 20 years just to figure out how to grow embryonic stem cells in the laboratory. More recently, though, molecular techniques have enabled swift movement on two fronts. Researchers are starting to see how stem cells can replenish their numbers while giving rise to specialized cells. Others are learning how to turn adult skin cells into cells more like their embryonic ancestors. These advances offer hope ... (p. 16)