In this issue of BioEssays, Chaudhari and Kipreos hypothesize that mitochondrial fusion promotes survival, especially in old animals, through the mechanism of maintaining energy metabolism. Along with the substantial evidence from their own work on C. elegans and studies on other model animals, the logic of the authors' argument is clear: first, aging is closely associated with the mitochondria's well-being; second, nine of ten lifespan extension pathways in C. elegans are associated with elongation of mitochondria via fusion, and elongated mitochondria are more efficient in producing ATP. Interestingly, the 10th pathway upregulates alternate energy generating pathways; third, maintaining ATP levels and energy metabolism supports longevity.

Practitioners in the relevant fields may have three questions about this hypothesis. Chaudhari and Kipreos well address them in the paper.