What if the secret to aging well isn’t found in expensive supplements or cutting-edge medical treatments—but in something as simple as moving your body? Evolutionary biologist Daniel Lieberman and neuropsychiatrist John Ratey explain why humans are built to stay active.
The research shows that exercise does far more than keep us fit. It rewires our brains, protects our cells from damage, and helps us age the way our ancestors did—staying healthy and sharp throughout our lives. Continue reading to discover why your body craves movement and how this commitment can lengthen and enhance your golden years.
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The Connection Between Exercise and Aging
Exercise significantly improves the probability of aging well—avoiding the health deterioration that often happens as we age. In his book Exercised, Lieberman cites evidence from modern-day hunter-gatherer societies to demonstrate that humans evolved to be physically active into old age, and avoiding a sedentary lifestyle helps us age well.
(Shortform note: In Lifespan, David Sinclair argues that exercise can greatly extend our lifespans, not just improve how we age. He says researchers have found that exercise lengthens and protects telomeres: small complexes of DNA and proteins at the ends of our chromosomes that get shorter each time a cell divides. When the telomere runs out, the cell stops dividing, leading to many of the problems of old age. Therefore, lengthening telomeres can literally keep our bodies younger for longer.)
We Evolved to Be Active Into Old Age
According to Lieberman, the Active Grandparent Hypothesis helps explain why physical activity is so effective at fighting senescence.
(Shortform note: In Lifespan, Sinclair expands on why senescence is problematic. Senescent cells aren’t able to perform their normal functions, but they also don’t die. Instead, they’re in a zombie-like state, clogging up previously healthy tissue with cells that can’t do their jobs. Furthermore, senescent cells can cause other cells to enter senescence, so the process only accelerates once it’s begun. Senescent cells send out chemicals that cause inflammation in surrounding tissue, which is associated with symptoms of aging.)
Compared to our primate relatives, we live much longer, way past our reproductive prime. According to the Active Grandparent Hypothesis, evolution favored longevity in humans because grandparents who were still around and active could help feed their grandchildren, ensuring the survival of their line.
Modern-day hunter-gatherer societies offer evidence to support this hypothesis because elderly members remain physically active well into their later years, continuing to contribute to their community’s survival. For example, among the Hadza of Tanzania, grandmothers often spend more time foraging than mothers do, and grandfathers travel similar distances as younger men to hunt and collect honey.
(Shortform note: In hunter-gatherer societies, elderly members’ active engagement doesn’t just benefit their physical health. This engagement also has social and cultural advantages. Older adults can pass on their wisdom, skills, and cultural traditions to younger generations, ensuring the continuity of cultural practices. Their engagement also fosters a sense of community and social cohesion, as all members are valued for their contributions and provided for as a result. For instance, researchers have found that Hadza foragers and hunters share their food with the rest of the community, including disabled or elderly people who are unable to help secure food.)
Unlike elderly members of hunter-gatherer societies, elderly people in industrialized societies typically become increasingly sedentary with age. This is problematic because the Active Grandparent Hypothesis means that grandparents—or elderly individuals—need to be active to benefit from the ways our bodies evolved to resist senescence.
Why is this? While humans were selected to live longer than most other species to help younger generations, this selection was only effective if the elderly remained physically active and productive. There was never evolutionary pressure to maintain health during a sedentary retirement. Instead, the optimal evolutionary strategy appears to be living long and actively, then dying relatively quickly when activity becomes impossible.
(Shortform note: Evolutionary pressure is the reason active grandparents were needed in the first place. In Sapiens, Yuval Noah Harari explains that, as humans started walking on two legs, women’s hips narrowed. The women who survived childbirth (and continued to pass on their genes) were the ones who gave birth early in the fetus’s gestation, when the baby’s head was smaller and undeveloped. The need to care for these vulnerable infants created unique social situations for humans, like relying on the community to help raise our children and shaping them through socialization to be whatever we want them to be. These situations and the resulting societal bonds may have contributed to the rise of human dominance in the animal kingdom.)
The Cellular Battle Against Stress and Aging
In his book Spark, Ratey contends that, for all of us, the toll a lifetime of stress takes on the brain becomes hard to escape. Characteristic features of aging, such as cognitive decline, depression, and dementia, are at least partially caused by the body’s cells being worn down by the stressors of life.
Ratey argues that, as your body becomes equipped to handle stress through exercise, it becomes better able to preserve its resources against the negative effects of aging. For example, as neurons wear out in the brain, the neural network thins—exercise counteracts this loss by supporting neuroplasticity and neurogenesis.
(Shortform note: Researchers have recently found that exercise has a neuroprotective role in staving off cell degeneration caused especially by aging, Parkinson’s, and Alzheimer’s. They advise that exercise should be used as an add-on therapy, together with other forms of treatment, to generate the most benefits.)
Compression vs. Extension of Morbidity
While elderly people in modern-day hunter-gatherer societies are more physically active than their peers in industrialized societies, hunter-gatherers still tend to have shorter life expectancies. Lieberman believes this suggests that physical activity compresses morbidity, allowing people to stay healthy for the time they’re alive. This is why hunter-gatherers typically remain healthy until shortly before their death. In contrast, elderly people in industrialized societies have an extension of morbidity: They live longer but experience long periods of disability and low quality of life before dying. According to Lieberman, the extension of morbidity is a consequence of lifestyle factors, such as a lack of exercise.
(Shortform note: Our modern approach to medicine might also be behind the extension of morbidity Lieberman describes. Sinclair, author of Lifespan, says that if we could prevent or reverse the effects of aging, then average life expectancy and quality of life would both skyrocket. But, instead of preventing or reversing the effects of aging, modern medicine treats one symptom of aging at a time, then sends the patient away until the next problem arises. As we age, those problems become more frequent and more severe until the treatments can no longer keep up, the body fails, and we die.)
Special Considerations for Women
Ratey writes that women face unique stressors related to menstruation, pregnancy, and menopause. The hormone fluctuations that attend each of these can lead to anxiety, depression, and attention problems, among other things. During pregnancy, maternal stress can have severe impacts on the fetus.
(Shortform note: A recent analysis found a strong correlation between exercise and the reduction of estrogen. High levels of estrogen have been linked to breast cancer. Subjects who exercised—especially at higher intensities—showed a modest reduction in the total levels of one form of estrogen.)
Ratey contends that exercise has a powerfully stabilizing effect in the midst of all the hormonal fluctuations women face in life. Strikingly, he notes that some data suggest it’s even capable of reversing some of the negative effects fetal alcohol syndrome has on the baby.
(Shortform note: Since the publication of Spark, researchers have continued to examine the impact of exercise on children with executive-function disorders, including fetal alcohol syndrome (FASD). The analysis found that children with FASD who exercised showed major gains in the areas of working memory and response inhibition, and they were also significant for attention. Another noteworthy finding of the analysis is that exercise-induced gains were higher for children with FASD and autism-spectrum disorders than they were for children with ADHD.)
It’s Never Too Late to Start
Lieberman notes that it’s never too late to benefit from increased physical activity and that the body’s repair mechanisms continue to respond to exercise even in old age. So, even if your body is already showing signs of senescence, starting to exercise today can make a difference.
(Shortform note: For older adults who haven’t exercised much, the notion that exercise is beneficial no matter how old you are is great news. That said, seniors may find it difficult to exercise regularly without injuring themselves, thereby doing more harm than good. To help avoid that problem, there are many exercise programs geared toward older adults, such as aquatic yoga classes.)
Learn More About Exercise and Aging
To better understand how physical movement helps us age slower and more gracefully in the broader context of health, take a look at our guides to Exercised by Daniel Lieberman and Spark by John Ratey.
