The five: chimeras created by science

A chimera is an organism with genetic material from two or more sources. Experiments in the field may save lives but are ethically controversial

Last week, researchers led by Spanish scientist Juan Carlos Izpisua Belmonte announced they had created the first human-monkey chimera embryos in China. The purpose of the experiment is to investigate ways of using animals to grow human organs for transplants. The organs could be genetically matched by taking the recipient's cells and reprogramming them into stem cells.