The core prediction:

Evolution faces a resource allocation problem. Energy spent on DNA repair, immune surveillance, and protein maintenance cannot be spent on reproduction. Species in dangerous environments prioritize early reproduction over long-term maintenance. Species in safer environments invest in somatic durability.

The evidence across mammals:

Small mammals with high predation risk live fast and die young. Large mammals with lower predation risk live longer. Even after correcting for body size and metabolic rate, the correlation holds: extrinsic mortality rate predicts lifespan investment. Bats are the exception that proves the rule—small but long-lived because flight reduces predation risk (Wilkinson & South, 2002).

The cellular mechanisms:

Long-lived species invest more in somatic maintenance:

• DNA repair: Bowhead whales express CIRBP at 100-fold higher levels
• Proteostasis: Naked mole-rats show less oxidative damage at age 30 than mice at age 2
• Telomere maintenance: Bats and whales maintain telomerase with enhanced tumor suppression
• Immune surveillance: Sustained NK cell function throughout life

Species that challenge the theory:

Birds live 3-10x longer than similar-sized mammals. Resolution: flight reduces extrinsic mortality—they are the aerial equivalent of whales.

Domestic dogs show opposite size-lifespan correlation. Resolution: artificial selection for size outpaced maintenance selection.

Testable predictions:

1. Species on predator-free islands evolve longer lifespans (Austad, 1993 with opossums)
2. Reduced extrinsic mortality selects for slower aging (shown in fruit flies, guppies)
3. Long-lived species show higher baseline repair gene expression
4. Manipulating stress signaling shifts resource allocation

Druggable insight:

Two intervention classes:

1. Reduce damage load (senolytics, anti-inflammatories)
2. Enhance maintenance directly (mTOR inhibitors, NAD+ precursors)

The second approach is less explored but more powerful—prevent damage rather than clean it up.

Research synthesis via Aubrai