It is tempting to think that as we get older, we have an excuse to take things easy and be less active. This would be the wrong approach, however, according to a team of evolutionary biologists and biomedical researchers at Harvard University. In the new study, the scientists outline the evolutionary and biomedical evidence supporting the idea that humans not only evolved to live many decades after they stop reproducing, but they also evolved to be physically active in this later stage of life.
“It’s a widespread idea in Western societies that as we get older, it’s normal to slow down, do less, and retire,” said Harvard evolutionary biologist Daniel E. Lieberman, the paper’s lead author. “Our message is the reverse: As we get older, it becomes even more important to stay physically active.”
The research team, which includes Aaron Baggish and I-Min Lee from Harvard Medical School, believes the paper offers the first detailed evolutionary explanation for why lack of physical activity as humans age increases the risk of disease and decreases longevity.
The researchers allude to other apes that have a longevity of only 35 to 40 years in the wild and do not survive much past menopause. This shorter lifespan is also associated with considerably less physical activity, suggesting a possible link between living longer and being more active.
“We evolved basically from couch potatoes,” said Lieberman, who has twice observed wild chimpanzees in Tanzania and been surprised by how much of their day is spent “sitting on their butts, digesting.”
Other evidence is provided by modern hunter-gatherers, who average about 135 minutes of moderate to vigorous physical activity a day. This level of activity – about six to ten times more than the level of the average American – may be one of the reasons that hunter-gatherers who survive childhood tend to live about seven decades.
Fossil evidence shows that lifespans that extended beyond the reproductive age were common by 40,000 years ago, contrary to the belief that human lifespans in prehistoric times were short.
The advantages of exercise are well-known, and older people are no different in terms of the benefits they can derive from keeping active. Indeed, the researchers emphasized that the key health benefit of physical activity is to extend the years that a person spends in good health.
The study discusses two routes whereby lifelong physical activity reallocates energy to improve health.
Firstly, the experts identified that physical activity helps to direct excess energy away from harmful metabolic mechanisms, such as fat storage. At the same time exercise also results in the allocation of more energy to carry out repair and maintenance in the body.
During exercise, calories are used up, but there is also damage to the tissues at the molecular and cellular level. The body responds to this by repairing the damage, for example by healing tears in muscle fibers, microfractures in bone and wearing in cartilage. This means that after recovering from physical exercise, we come back stronger than we were before.
Exercise also leads to the release of certain antioxidants and anti-inflammatories, and enhances blood flow. In the absence of physical activity, these responses occur less often. Some of these repair processes have been shown to lower the risk of diabetes, obesity, cancer, osteoporosis, Alzheimer’s disease, and depression.
“The key take-home point is that because we evolved to be active throughout our lives, our bodies need physical activity to age well. In the past, daily physical activity was necessary in order to survive, but today we have to choose to exercise, that is do voluntary physical activity for the sake of health and fitness,” said Lieberman.
Levels of physical activity have been decreasing worldwide, as machines and technology replace human labor. We no longer have to forage actively for food and our leisure time is spent largely in front of a screen. The advice of the research team, which also includes graduate students Timothy Kistner and Daniel Richard, is that we should get out of our chairs and do some exercise.
“The key is to do something, and to try to make it enjoyable so you’ll keep doing it,” said Lieberman. “The good news is that you don’t need to be as active as a hunter-gatherer. Even small amounts of physical activity – just 10 or 20 minutes a day –substantially lower your risk of mortality.”
The study is published today in the journal PNAS,