Ouroboros looks at the unknowns of IGF-1 signaling. It is clearly important to aging and longevity, but we are still left with many unanswered questions: "it has become apparent that single gene mutations in the insulin and insulin-like growth-factor signalling pathways can lengthen lifespan in worms, flies and mice, implying evolutionary conservation of mechanisms. Importantly, this research has also shown that these mutations can keep the animals healthy and disease-free for longer and can alleviate specific ageing-related pathologies. These findings are striking in view of the negative effects that disruption of these signalling pathways can also produce. ... The underscored passage brings up an issue that we've discussed here previously: Why is it that IGF-I pathway mutations can confer long healthy lives on organisms, even though supplementation with IGF-I is often quite beneficial, and depletion of IGF-I is often bad for individual organ systems? Indeed, according to another recent study, low doses of IGF-I appear to protect the mitochondria in aging rodents - why then do completely IGF-I-deficient animals enjoy extended and healthy lives?"