The earth's magnetic field protects us from charged particles of the sun's radiation and cosmic rays. It is mysterious therefore that magnetic field reversals, during which there is evidence that the geomagnetic field significantly decreases in strength, do not correlate with mass extinctions.
Hypothesize that organisms on earth (probably land organisms) have evolved to survive higher radiation during magnetic field reversals. This is amazing as it is a capability needed extremely rarely.
What are the survival mechanisms? Of course, DNA repair and apoptosis are two. Hypothesize that cancer is also counterintuitively a survival mechanism, inspired by "The final checkpoint. Cancer as an adaptive evolutionary mechanism". During periods of high radiation, cancer kills off some mutated members of the species before they can reproduce. The mutated ones which do reproduce pass on their mutated genes to the next generation, but we hypothesize that the offspring have higher susceptibility to cancer so they may not live long enough to reproduce. In this way, the species survives mostly unchanged, avoiding propagating harmful mutations. Species which have lower susceptibility to cancer, while seemingly advantageous during periods of high radiation, actually end up mutating away from optimality and it will be a much slower path of evolution to recover it, during which time they might get killed off or crowded out by species which survived better.
Human meddling with cancer, trying to survive it in the short term, may have drastic long-term consequences.
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