Chance is hugely significant in biology. In fact, the presence of apparent randomness in so many aspects of biology - from mutations in DNA to the chance involved in that one sperm reaching that one egg that became you - suggests that randomness is useful, even necessary, in very many cases.
In our evolutionary narratives, the organism itself often seems to play a passive role: a powerless victim, almost, of changes to its environment or mutations in its genes.
Just as your own existence is unlikely and far from inevitable, the evolution of modern humans as a species depended on a whole string of chance events - some happening in the environments our ancestors inhabited, and some inside their own bodies, including random mutations in their DNA.
My idea right from the beginning, I guess, was to dismantle the immune system one gene at a time so we could track the mutations that cause problems.
In the early '90s, we discovered mutations that could double the normal life span of worms.
First of all, many human diseases are influenced by, if not caused by mutations in genes.
There are certain mutations you can find across cancers in different organs.
This seems highly likely, especially as it has been shown that in several systems mutations affecting the same amino acid are extremely near together on the genetic map.