Differential Aging
The human body is not a homogeneous mass, but rather a networked collection of very different structures and systems. Unsurprisingly, then, aging affects different tissues at different rates. This is just the same as in any engine, simple or complex: some components tend to fail due to accumulated damage more rapidly than others. For example:
The 80-year-old Norwegian received a cornea transplant fifty years ago, a piece of tissue now 123 years old that still works today. It could be the oldest eye, or even human body part, still functioning or to have ever been in use for so long. ... He had a cornea transplanted into his right eye in 1958, from a man born in June 1885. At the time it was expected to work for only 5 years. However, Reuters report that the procedure has been in use since the early 20th century. That means there could be even older corneas out there.
There is no profound lesson to be learned here, but this another useful example to present to people unfamiliar with the bounds of life span and survival in the natural world. If tortoises, whales, and this cornea can all manage such lengthy survival, it encourages the belief that medical research can engineer the same for human life in general. It is easier for people to accept that a goal can be accomplished based upon the evidence of a near example already in existence than in the absence of any example at all.