Adult tissue stem cells have the capacity for asymmetric self-renewal, which means they can divide to produce differentiating cells but not differentiate themselves. Embryonic stem cells do not have the capacity of asymmetric self-renewal. In order to produce differentiating cells, they themselves must differentiate, too. Embryonic stem cells also have the problem of high levels of mutation and tumor-formation. Adult tissue stem cells do not. Embryonic stem cells differentiate into immature tissues that are not found in the body after birth. Adult tissue stem cells produce mature differentiated cells like the ones found in the body after birth.