Figure 4. Increasing Canine and Human Risk due to Surpassing the Species’ Respective Evolutionarily-Determined Lifespan Barriers.

A) Multicellular species, represented here by bowhead whales, African elephants, African naked mole rats, ancestral humans, modern humans, ancestral dogs, and modern dogs, have achieved an evolutionarily derived balance between tumor suppressive mechanisms and senescence mechanisms that have selected for lifespans that are consistent with their respective evolutionary pressures. Recent technological advances have led to lifespans in humans and dogs that are more than twice as long as those to which each species had adapted over millions of years of evolution. The vast majority of cancers occur after individuals cross this evolutionarily adapted lifespan (dashed line) for B) humans and C) dogs. Neither species has had the time, nor has it been subjected to selective pressures, to establish a new evolutionary balance that resets its cancer barrier.