wall st journal: These entities, created through a variety of techniques, have been studied at only the earliest stages of development. By Amy Dockser Marcus
'In some cases, scientists have taken cells from an embryo and manipulated them to generate another embryo-like entity. Other experiments involve reprogramming adult cells to grow into entities that mimic certain organs, like the human brain.
'The entities aren't intact embryos. But scientists at Harvard University, the Rockefeller University and other institutions say they have been surprised by the remarkable ability of some cells to self-organize and develop in ways similar to an embryo, independent of biological input from a mother. Some appear to develop what is known as the “primitive streak,” a band of cells in embryos believed to precede the initial steps of brain formation.'