33 Essays on Infinite Lifespans   Aubrey de Grey extends their healthy lifespan by at least two decades. What will such care comprise? As I have discussed extensively elsewhere, [8–10] there seem to be only seven broad categories of molecular and cellular dif- ference between older and younger people that we need to fix to achieve two decades of human life extension (“seven deadly things”). These consist of a decline in the number of cells in certain tissues and an accumulation of unwanted cells of cer- tain types, of mutations in our chromosomes, of mutations in our mitochondria, of random cross-links between long-lived extracellular proteins and of chemically inert but bulky ‘junk’ in our lysosomes and in extracellular spaces. Further, I have delineated [8;10–13] approaches to either repairing  or  obviating  (stopping  from  being  pathogenic however much they accumulate) all these changes. All these approaches  are  already  technically  feasible.  The  underly- ing precursor technologies have already been developed and the work needed to complete them can be described in con- siderable detail. I have termed these projects ‘Strategies for Engineered  Negligible  Senescence’  (SENS)  [8–10],  since their goal is collectively to eliminate from humans the posi- tive correlation between age and risk of death per unit time – biogerontologists’ formal definition of senescence. Unfortunately, most of the first-generation SENS therapies will be not only risky and laborious but also partial. A thor- ough survey of this issue exceeds the scope of this essay, so I will discuss just one illustrative example here: the breaking of extracellular protein-protein crosslinks. Most such links are laid down by a process called glycoxi- dation, in which proteins react with sugars in the circulation to  form  adducts  that  can  rearrange  and  undergo  subse- quent, oxidative reactions forming linkage to a neighboring protein. [14] Such crosslinks are eventually harmful to long- lived extracellular structures, especially the artery wall, because