Much of longevity and aging research focuses on studying extremely long-lived species, including bats, naked mole-rats and bowhead whales, to find genetic changes that contribute to long life.

However, such work has yielded highly species-specific genetic changes that are not generalizable to other species, including humans. As a graduate student, I have studied growing evidence, including recent work from my advisers' labs (Maria Chikina and Nathan Clark), that supports the hypothesis that lifespan is a complex and highly context-dependent trait that calls for a shift in how biologists think about aging.

Old age: The human problem

Aging is the process by which the likelihood of death increases the longer an organism is alive. In mammals, aging is hallmarked by several molecular changes, including the breakdown of DNA, a shortage of stem cells and malfunctioning proteins.

Numerous theories that exist to explain why aging happens fall into two categories. "Wear-and-tear" theories postulate that essential processes simply wear out over time. On the other hand, "programmed death" theories assert that specific genes or processes are designed to drive aging.

Traditional definitions and aging theories are human-centric, and when we examine aging from a cross-species perspective, it becomes clear that human aging is unique. In fact, among animals there is no typical way to age.

Humans show low mortality rates until a sharp spike in mortality at very old age, around 80 years. Most mammals have relatively less increase in mortality with age and more consistent mortality through their lifespans. Some mammals, such as the tundra vole and the yellow-bellied marmot, show virtually no increase in mortality with age. In other words, older individuals are equally as likely to die as younger individuals, possibly because aging does not impact survival.

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