Thesis #25 – Repairing all forms of cumulative damage and altering all types of regulatory signaling during the aging phase will also fail to fully alleviate aging, because some features of aging will arise from the absence of structural gene-products required to sustain health indefinitely during adulthood as a result of the de-tuning of adaptation with age.

But not all failures of adaptation at later adult ages will be due to damage or poor coordination.  Sometimes the endogenous deaths of adults arise from the absence of necessary bits of machinery, from the level of the cell to that of the entire organism.

It is at the level of the whole organism that this failure of evolution to supply “missing parts” is most obvious.  The rapidly deteriorating adult mayfly lacks mouthparts.  Its sole role as an adult is to find a mate, copulate, and, if female, deposit its eggs appropriately.  This is also true of many moth species, which also entirely lack functional mouths as adults.  Evolution’s failure to sustain mouths in some adult insects is a fairly extreme failure to supply a part whose lack dooms them to deterioration and an early death.

With somewhat greater subtlety, vertebrates vary widely in the availability of replacement teeth.  Humans get just two sets in their lives.  Elephants get six.  But in either case, absent dentistry, once we have lost too many of our ultimate set of teeth, our subsequent nutrition will be impaired.

By this same biological logic, there is no reason for natural selection to supply our cells with enzymes that might catalytically prevent or repair sundry types of damage or dysregulation at indefinitely great ages with full efficacy.  Evolution will produce biochemical bits of cell machinery that sustain function at every age, if there is no trade-off or separation between these functions at different ages.  Worse still, if evolution by natural selection faces a trade-off between earlier and more prolific reproduction and the provision of missing components that might sustain life indefinitely, the declining forces of natural selection combined with this antagonistic pleiotropy will ensure that the later adult will be missing key features required to sustain life infinitely.