| Without any direct evidence (although it's an idea I picked up from attending various immunology lectures), it seems like aging/death is at least partially linked to immunity. Our ancient ancestors had to make a tradeoff in order to combat the extremely high mutation rate of their microbes, by increasing their own rate of genomic diversity (through sex, and through adaptive immunity) including in the receptors which detect microbes. Sexual reproduction
https://en.wikipedia.org/wiki/Sexual_reproduction V(D)J recombination
https://en.wikipedia.org/wiki/V(D)J_recombination Evidence of G.O.D.’s Miracle: Unearthing a RAG Transposon
https://www.sciencedirect.com/science/article/pii/S009286741... However, nothing is free, and with the ability to generate this extreme genetic diversity comes a higher risk of making mistakes including un-programmed DNA breaks, etc.. All these little mistakes add up as aging, and sometimes cancer, when the repair pathways are not able to keep up with the damage. Also, by having an adaptive immune system you're constantly breeding tougher and tougher microbes, which could be considered harmful. The acquired immune system: a vantage from beneath https://pubmed.ncbi.nlm.nih.gov/15539148/ |
Mucus acts as both a barrier and a food source with an extremely diverse O-linked glycans which decorate its backbone. ~800k permutations of the 5 possible O-linked if you consider a glycan chain of length 5, and 3 possible linkages types. In actually the diversity is likely greater given chain branching patterns, randomized expression of glycosyl hydrolases which generate the mucus, etc..