In western nations, it's common to believe that we should slow down, do less, and retire as we become older. Wondering if this is actually true, a group of Harvard biochemical researchers and biologists decided to put the so-called 'active grandparent hypothesis' to the test.

The team believes that their study (published in PNAS) offers the first elaborate evolutionary explanation for why the absence or inadequate amount of physical activity as humans age increases the risk of disease risk and shortens life span.

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This is the story of how and why physical activity was built into human biology. The study's central message is that, contrary to what you may think, as we age, it becomes more important to stay physically active.

The researchers discovered that humans evolved to continue living several decades after their reproductive phase has ended but also evolved to be comparatively active in their autumn years.

Primates

As a starting point, the researchers looked at humans' primate cousins. The scientists point out that apes, which have a lifespan of approximately 40 years in the wild and seldom survive into menopause, are far less active than most people, signifying that human evolution selected not only for longer lives but also for greater physical activity at a later point in life.

According to evolutionary biologist Dr. Daniel E. Lieberman, lead author of the paper, we essentially evolved from what you may call 'couch potatoes.' Lieberman, who monitored one of our primate cousins, chimpanzees, in their natural habitat, was stunned by the enormous amount of time these creatures spent 'sitting on their buts, digesting' as he mentioned it.

The findings mentioned above are particularly jarring in comparison to hunter-gatherers, who engaged in roughly 135 minutes of moderate to strenuous physical activity per day on average. Those 135 minutes constitute approximately eight times as much time of active engagement compared to what the average modern-day human spends.

Contrary to popular belief, fossil evidence shows that humans had fairly long lifespans 40 thousand years ago. The impressive amount of physical activity may be one of the principal factors of why hunter-gatherers (given that they pull through childhood) commonly lived to be about 70 years, which is a long time past the age at which we generally stop having offspring.

Why physical activity allows for a longer life

The science team looked at two ways that lifetime physical exercise helps people to re-allocate energy and enhance their health. The first is to divert surplus energy away from potentially damaging mechanisms such as fat accumulation.

The researchers also learned that physical exercise affects how much energy is allocated to repair and maintenance operations. Physical exercise, in addition to burning calories, is physiologically stressful, causing harm to the body at the molecular, cellular, and tissue levels, according to the study. The body's response to this harm, on the other hand, is to rebuild itself stronger.

Rebuilding incorporates repairing cartilage damage, restoring tears in muscle fibers, and mending microfractures. The body's reaction to physical activity also causes the release of exercise-related anti-inflammatories, antioxidants and improves blood flow.

In the absence of physical activity, these reactions are engaged less. The cellular and DNA repair processes have been demonstrated to reduce the risk of osteoporosis, diabetes, depression, obesity, cancer, and Alzheimer's disease. All in all, no small matter.

How to live for longer

Lieberman stated that the most important thing to take from their study is that our bodies need physical activity to age well because we evolved to be active throughout our lives.

Historically, everyday physical engagement was essential for survival. However, in modern times, we need to actively decide to engage in physical activity as no direct external factors force us to. In fact, the amount of time spent doing physical activities decreases as technology continues to fill in traditional physical work.

The team encourages us to get out of our seats and try to do something physically active that we enjoy enough to stick to it. We don't need to be as active as we were 40.000 years ago as even limited daily activity (approximately 20 minutes) will considerably enhance your chances to have a long life.

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