Book SummaryExercised, by Daniel E. Lieberman

1-Page Summary1-Page Book Summary of Exercised

We know we need to exercise to stay healthy, but lacing up and going for a jog can feel like fighting our most basic instincts. Why? According to Daniel Lieberman, it’s because humans evolved to conserve energy. Our ancestors did a lot of daily physical activity for survival, not for fitness. When our ancestors weren’t busy finding food, caring for children, or avoiding danger, they rested. Rest ensured they had enough energy for what mattered most: reproducing.

(Shortform note: Another way to understand Lieberman’s concept of energy conservation is by comparing it to the economic principle of supply and demand. In economics, resources are allocated based on demand, and efficiency is achieved by minimizing waste. Similarly, our bodies allocate energy based on perceived needs, conserving it when the demand for energy is low. However, unlike economic systems that can adapt rapidly to changing conditions, our bodies have a slower response to the drastic shifts in lifestyle brought about by modern technology. This lag results in a mismatch between our evolved physiology and our current environment, leading to health problems associated with inactivity.)

Our modern lifestyle releases us from the need to do physical activity to survive. Today, most of us no longer hunt, grow food, or walk several miles to find water and shelter. But Lieberman argues that our bodies still expect physical activity. So, it’s important for us to exercise—to engage in voluntary physical activities. When we don’t, we become sick.

(Shortform note: Why are we less active than people were in the past? Some experts point to the development of technology, rather than any other cultural or economic shifts. When machines take over jobs that previously required physical labor, we end up with fewer reasons to get moving. Research shows that 100 years ago, people got an average of [five times more daily...

Exercised Summary Our Ancestors Didn’t Exercise

Lieberman’s studies of pre-industrial communities and our primate ancestors led him to the realization that humans never evolved to exercise. The voluntary physical activity we do to achieve health and fitness goals is a modern concept, as our ancestors engaged in physical activity out of necessity rather than for health benefits. This section explores why humans evolved to conserve energy and how our bodies evolved to do this.

Why Humans Evolved to Conserve Energy

Lieberman argues that we evolved to conserve energy and avoid unnecessary exertion—not out of laziness, but as a survival advantage. Organisms have a limited number of calories to spend on competing needs: growing, maintaining and healing the body, storing energy for times of scarcity, powering necessary activity, and reproducing.

From an evolutionary perspective, it makes sense to avoid unnecessary physical activity, as those calories could instead be used for reproduction or survival. Lieberman explains that the human body expends significant energy even at rest, with basic bodily functions spending around 1,700 calories per day for an average adult male.

**Being physically inactive might be our...

Exercised Summary Modern Humans Need Exercise

Although our ancestors didn’t exercise, modern humans should. That’s because our ancestors had to work much harder than us for fewer calories as they foraged for, hunted, or grew their own food. The modern benefit of easy calories and easy living comes at a cost: exercise.

This section will explore why modern humans need to exercise even though our ancestors didn’t. It will also discuss how exercising prevents disease and senescence, the gradual deterioration of health that we typically associate with aging.

Our Modern Bodies Need Exercise

As we’ve seen, surviving and reproducing was our ancestors’ full-time job. Their lifestyles included daily, moderate physical activity and securing just enough calories to survive and reproduce. However, most modern humans lead lifestyles where daily moderate physical activity isn’t necessary for survival, and we have access to more calories than we need.

Although our lifestyles have changed dramatically, our bodies haven’t caught up. According to the Costly Repair Hypothesis, our bodies require physical activity to maintain health. When we exercise, our bodies release stress hormones, cells leak harmful chemicals...

Exercised Summary Evolutionary Answers for Modern Fitness Questions

We’ve discussed why exercise is healthy despite humans not having evolved to exercise. Now, we’ll explore Lieberman’s advice for your well-being based on his insights from evolutionary science and anthropology. This section will discuss his insights on motivating yourself to exercise, what kind of exercise to do, and how much to exercise.

How Can You Motivate Yourself to Exercise?

Lieberman explains that evolution made us resistant to unnecessary physical activity. He advocates making exercise fun, social, and necessary to overcome this resistance.

Make Exercise Fun and Social

Fortunately, exercise triggers reward systems in the body that help us find physical activity enjoyable. It releases chemicals like [restricted term], serotonin, and endorphins that give us a rush of excitement and pleasure, and even endocannabinoids that trigger a meditative state—a “runner’s high.” However, these chemicals only start working once you’ve started working out, so they don’t offer motivation to get started. In addition, Lieberman points out that these reward systems work best in people who are already physically active, making it harder for sedentary...

Shortform Exercise: Plan Your Evolution-Informed Workout

Lieberman offers suggestions for exercising to prevent or heal diseases and avoid senescence. Plan your workout routine with his insights in mind.

First, outline goals for your workout routine. Are you trying to prevent or heal a specific ailment, such as type 2 diabetes or depression? Are you hoping to stay active as you age? Be as specific as possible.