Totipotent stem cells are unique cells that have the ability to develop into any type of cell in an organism, including both the embryonic and extra-embryonic tissues. This means they can form not only the body of an organism but also the supporting structures like the placenta. Totipotent stem cells are present in the earliest stages of development, specifically right after fertilization. As development progresses, these cells begin to specialize, losing their totipotency. After a few divisions, they become pluripotent stem cells, which can still differentiate into many cell types but cannot form an entire organism. Understanding totipotent stem cells is crucial for research in regenerative medicine and developmental biology.