69 Essays on Infinite Lifespans   Michael D. West conditions they always eventually exhausted this ability and arrested their growth. When I entered the field of aging research in the late 1970’s, Hayflick’s  observation  was  already  dogma.  Humans  are  an amalgam of cells, some mortal and others immortal. Everyone is painfully aware of the mortal ones. Like bricks that are mor- tared side by side to construct the walls of buildings, so our cells are cemented together to form the tissues of our bodies. And those tissues – our bones, blood, and skin and the cells from which they are made – are all destined to age. We are made  of  mortal  stuff.  Our  body’s  cells  and  therefore  our bodies themselves share a common sentence of death. So, it may surprise you to learn that there is an exception. HEIRS OF OUR IMMORTAL LEGACY Still resident in the human body are potential heirs of our immortal legacy, cells that have the potential to leave no dead ancestors; cells from a lineage called the germ-line. These cells have the ability for immortal renewal as demonstrated by the fact that babies are born young, and those babies have the poten- tial to someday make their own babies, and so on, forever. In 1997, we at Geron Corporation, along with a host of collaborators, finally succeeded in isolating the gene that we reasoned should impart this capacity for unlimited replica- tion  in  germ-line  cells.  The  gene  encodes  a  protein  called telomerase that rewinds the clock of aging at the ends of the chromosome. The isolation of this ‘immortality gene’ stirred considerable  controversy  as  to  its  potential  to  ‘rewind’  the Hayflick clock in cells in the human body after we showed that it actually works on cells cultured in a laboratory dish. Introducing the gene in an active state literally stops cellu- lar aging. The cells become immortal but are still otherwise