A unified theory of cell differentiation, aging, and cancer is discussed. All cells are
hypothesized to originate from stem cells. These stem cells mature as they divide and
eventually reach a fully differentiated cell, which cannot divide. Aging is caused by the loss
of stem cells, either due to cell death or terminal differentiation, and by eventual death of fully
differentiated cells. Both loss of stem cells and death are brought about by oxygen radicals.
The cancer phenotype is caused by an inability of a stem cell to differentiate fully under the …