STORY AT-A-GLANCE

• Jacob Kimmel, president and co-founder of NewLimit, a company that develops reprogramming medicines for aging, discusses how evolution only optimized humans to survive through reproduction, not a long lifespan

• Aging reflects weak evolutionary pressure for longevity, which leaves your cells vulnerable to decline after their most productive years

• High mortality in early human history favored intelligence for survival, with fluid intelligence peaking in early adulthood to match evolutionary priorities rather than preserving cognitive strength into later life

• Unlike microbes, humans didn’t evolve antibiotics due to genetic stability constraints. Instead, your adaptive immune system emerged as a flexible defense, leaving traces of ancient viral battles in your DNA

• Epigenetic reprogramming challenges evolution’s limits by reversing cellular decline, offering a way to extend healthspan

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Human life today is the result of millions of years of evolution, shaped by forces that favored survival and adaptation. You might think that the same process would have extended health and resilience into later life. Yet longevity was not a priority in the evolutionary blueprint, and the result is a body that wears down with age rather than one designed for lasting vitality.

This paradox is the focus of an interview on the Dwarkesh Podcast, featuring Jacob Kimmel, president and co-founder of NewLimit, a biotechnology company developing reprogramming medicines for aging.1 In their discussion, Kimmel shares his insights into how evolution shaped the limits of human lifespan and what modern science can do to change that trajectory.2

The Evolutionary Trade-Offs That Left Humans Aging Fast

Your body’s aging process reflects choices made by evolution, balancing survival against a complex web of constraints. Kimmel identifies three key factors that explain why natural selection didn’t equip you with a longer, healthier lifespan. By viewing evolution as an optimization process with limited resources, he unpacks why your cells and systems decline over time, revealing trade-offs that favored immediate needs over long-term vitality.3

• Evolution only needed you to reach reproduction — Natural selection favored traits that carried humans into their childbearing years and allowed them to raise children, but it applied little pressure beyond that point. As Kimmel explains, in human and primate history, the daily chance of dying (what he called the “baseline hazard rate”) from infection, predators, or accidents was extremely high.

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  If most lives ended around 40, there was no evolutionary incentive to shape traits that would keep you vigorous at 60. “The number of individuals in the population that are going to make it later in that lifespan, where using some of your evolutionary updates to try and push your lifespan upward, is relatively limited,” Kimmel said.4

• This high hazard rate also influenced traits like intelligence — Longer childhoods made it possible for humans to develop larger, more capable brains, but stretching adolescence too far carried the risk of dying before reproduction. This is reflected in your fluid intelligence, the ability to reason, solve new problems, and think flexibly without relying on prior knowledge or experience,5 which peaks around your 20s or 30s.

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  Evolution optimized for cognitive prowess when you were most likely to contribute to the group, not later in life. Mathematical discoveries often occur before age 30, suggesting your brain’s peak aligns with the age of maximum population contribution during evolutionary history.

• Evolution may have even favored shorter lifespans — Kimmel explains that, from the perspective of the “selfish gene,” older individuals who are less fit and still consuming resources could reduce a group’s overall survival.

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  If you live longer but contribute fewer calories or gather fewer resources than younger members, your extended presence actually lowers the group’s fitness. In this sense, evolution tends to favor turnover, giving younger and more productive individuals the chance to propagate genes more effectively. According to Kimmel:

  “There is a notion by which a population being laden demographically with many aged individuals, even if they did have fecundity persisting out some period later in life, is actually net negative for the genome's proliferation and that really a genome should optimize for turnover and population size at max fitness.”6

• Longevity sits within the constraints on evolution’s optimization process — Kimmel describes the genome as a set of parameters and natural selection as an optimizer with limits. Mutation rates need to stay low to prevent catastrophic errors such as cancer, and small population sizes restrict how many genetic variants can be tested.

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  At the same time, your ancestors were locked in a constant battle with infectious disease, which absorbed much of evolution’s attention. These constraints left little room to fine-tune traits related to longevity, even if longer life might have offered some benefit.

Kimmel stresses that aging is not a single flaw that evolution could have easily corrected, but a multi-causal process shaped by many layers of molecular regulation. The decline in your cells’ function comes from accumulated changes in gene expression and resilience, not from one defect. This complexity explains why evolution didn’t simply “fix” aging and why interventions need to target multiple pathways to extend your healthy years.

Why Humans Didn’t Evolve Their Own Antibiotics

When Kimmel discussed the evolutionary limits on human biology, he pointed to antibiotics as an instructive example. Your body’s ability to fight infections relies on intricate defenses, but you might wonder why evolution never equipped you with built-in antibiotics like those produced by microbes. Instead, your immune system evolved as a flexible alternative to antibiotics, shaped by pathogens.7

• Microbes produce antibiotics through a unique evolutionary advantage — With vast population sizes and extremely high mutation rates, bacteria and fungi engage in chemical arms races, churning out molecules like antibiotics to outcompete rivals. This process allows microbes to rapidly adapt, producing diverse compounds that target specific competitors in their environment.

• Humans, by contrast, could never evolve along this path — Our mutation rates need to stay relatively low in order to protect the stability of our complex genomes. Rapid mutation at microbial levels would lead to catastrophic consequences, most notably uncontrolled cancer. This constraint means that while microbes thrive on variation, mammals depend on genetic stability to survive from one generation to the next.

• Because of these biological limits, humans developed a different defense system — Instead of producing chemical antibiotics internally, you evolved an adaptive immune system capable of learning and remembering threats. This approach provides flexibility without relying on high mutation rates. It also allows your body to respond to a wide variety of pathogens across your lifetime, even as they change and adapt.

• Your DNA still carries the marks of past battles with pathogens — Over millions of years, infectious diseases shaped survival, and the genetic record shows the defenses your ancestors developed against those th