Soma, Germ, Stem and Immortality

Abstract: A longstanding question in biology is why life deteriorates and ultimately ceases. This relates to causal phenomena such as aging, disease, predation and parasitism, which manifest at species scales as relationships between body mass and longevity, and body mass and metabolic rate. Nevertheless, some species appear to defy what millennia of evolution has put into place. Explaining extremes in longevity, including those associated with the relaxation or absence of aging is a fundamental evolutionary puzzle. I present a survey of factors that contribute to explaining aging and lifespan, focusing on the distinctions between soma and germ line and how stemness – cells with the power to either replicate themselves or to produce organism-level functional, differentiated cells – is likely key in explaining how and why certain species appear to relax or escape mortality. I show that stemness is found at different levels of biological organization and speculate on a simple classification of system types.