In the early 1960s two Canadian scientists, Ernest McCulloch and James Till discovered stem cells. They did this by injecting bone marrow cells into mice that had been irradiated, then after recording the appearance of the new nodules on the spleens of the mice they were able to prove that the bone marrow cells functioned as the long-postulated stem cells would, these cells were self-renewing. [9]  

 Then in 1981, Matthew Kaufman and Martin Evans were able to successfully take cells from the embryos of mice cells that were capable of morphing into different types of cells and that were able to renew themselves perpetually and without further differentiating. Martin Evans named these cells embryonic stem cells.[12]

 In 1998 the first human embryonic stem cell line grew from the tissue of leftover embryos at a fertility clinic. This was accomplished by James Thomson, a cell biologist. [9]