From a logical point of view, cell division is regulated by the environment and by the ability of the cell to respond to the environmental signals. The terminology of the cell cycle, the elaborate mathematical models, and the kinetic analyses are all convenient notations and descriptions of the behavior of populations of cells. However, they tell us very little about the fundamental molecular mechanisms that control cell proliferation. Stated in other terms, what controls cell reproduction are growth factors in the environment and genes and gene products inside the cell or at its surface....