Hydra are functionally immortal, given a suitably static environment. They exhibit continual proficient regeneration, and their mortality risk is low and constant over time. As a species they appear near unique in this. Why is aging and imperfect regeneration almost universal among species? One explanation is that environmental change gives aging species an advantage: non-aging species can certain emerge in eras of comparative environmental stability, but will be out-competed when the environment shifts. Other explanations involve the more complex structure in higher species, particularly in the central nervous system, where data must be stored as lasting molecular and cellular structures. Long-term persistence of fine cellular structure and proficient, continual regeneration don’t go well together.
This study looks at the complexity and structure of the nuclear envelope inside cells as a possible dividing line between the few immortal species such as hydra and all of the others. The authors propose that increased complexity of the nuclear structure, and thus its greater vulnerability to certain kinds of molecular damage known to be associated with aging, limits the degree to which longevity and highly proficient regeneration can evolve – though I think that
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