Stem cells at one point in time turn into specilized cells, how do they know what specialized cell to turn into? Every stem cell has every trait of that organism, so it can be transformed into any specialized cell, but how does the stem cell know what genes to "turn on"? For example, how does a stem cell know to "turn on" the lung cell genes when in the lungs rather than just "turning on" the skin cell genes? What in the lungs causes the stem cell to turn into a lung cell? If you say the surrounding cells, well it all had to start somewhere...