Consider the following possibilities:
- Higher organisms have better DNA repair and live longer than lower organisms. A correlation exists but it is neither causal nor contributory (neither a major nor a minor contributor).
- Higher organisms have better DNA repair than lower organisms, and in part because of this, live longer. Better DNA repair contributes to or drives (is the major contributor to) greater longevity.
- Higher organisms have better DNA repair than lower organisms, and solely because of this, live longer. Better DNA repair is the sole cause of their greater longevity. DNA damage is solely responsible for senescence and death.
Of the three possibilities listed, #2 is the most likely. The effect on longevity might be small, medium, or large. The best experiment is hard to do:
- Create a sufficiently large cohorts of different types of higher organisms whose DNA repair is no better than that of a mouse, and compare their longevity with mice and with other members of the higher species whose DNA repair is wild type. If possible, change nothing else. Of course, it is not possible to change nothing else. Intrinsic complexity rules! Interpretations are always suspect even when most people think they are crystal clear.