Human evolutionary biology and how our modern environment is causing modern diseases - The Diary of a CEO with Dr Daniel Lieberman
Understanding Mismatch Diseases and Human Evolution
Most people in the Western world are likely to die from a mismatch disease, which are conditions for which human bodies did not evolve. These are caused by novel environmental conditions to which humans are inadequately or imperfectly adapted. Examples include obesity, heart disease, many cancers, allergies, autoimmune diseases, and chronic stress.
Daniel Lieberman, a Professor of Human Evolutionary Biology at Harvard University, studies the human body's evolution, particularly in physical activity and diet, to understand these modern health crises. He emphasizes that understanding our evolutionary history is crucial because humans evolved, they were not designed or engineered.
While human ancestors were hunter-gatherers for millions of years, the idea that their lifestyle provides all the answers for modern health is a "Paleo fantasy". Natural selection primarily cares about reproductive success, not happiness or optimal health, so ancestral practices are not always optimal for health today.
Humans are the ultimate omnivores, capable of eating almost anything due to a flexible digestive system and technology like cooking and food processing. There is no single "evolved" human diet. Humans began eating meat at least 2.5 million years ago, which played a significant role in evolutionary history.
The evolution of the hunting and gathering lifestyle between three and two million years ago was transformative. This period saw the emergence of stone tools, butchering, cooperation, communication, and extractive foraging for high-quality underground foods.
Key human adaptations include an external nose (around 2 million years ago) that acts as a humidifier, preventing lungs from drying out and recapturing moisture during activity. Additionally, humans developed an increased density of eccrine sweat glands across their bodies and lost fur, enabling efficient evaporative cooling, which was a huge advantage for hunting in hot environments.
The increase in human brain size around 2 million years ago is linked to the hunting and gathering system, which made more energy available through processed foods, cooperation, and new food sources like meat and marrow. Brains are metabolically expensive, consuming a significant portion of the body's energy.
Humans are born unusually fat (infants are about 15% body fat), which is a fundamental adaptation. This body fat acts as an energy reserve, crucial for supporting large, energy-demanding brains (especially in infants) and for financing the high energy costs of reproduction (pregnancy and nursing). Our predisposition to store fat is fundamental to the species.
Modern Lifestyle and Health Consequences
Back pain is the number one medical complaint, largely due to weak back muscles caused by prolonged sitting in comfortable chairs. The best predictor of preventing back pain is the endurance strength of back muscles. Sitting a lot at work and in leisure time significantly increases disease risk. Interacting sitting bouts by getting up frequently (e.g., every 20 minutes) is crucial.
Claims that solely breathing through the nose can fix all health problems are viewed skeptically. Humans evolved to mouth-breathe while running to dump heat efficiently. Simple solutions for complex health problems are often misleading.
The modern abundance of food choices, unlike the past where people ate what was available, leads to many poor dietary decisions. Simplified dietary approaches (e.g., "just be a vegan") often ignore complexities and trade-offs.
Cultural evolution is much faster than biological evolution, leading to a rapid transformation of environments that our slow-changing biology cannot keep up with. This mismatch intensifies many health problems.
Myopia (nearsightedness) has increased significantly in recent decades, primarily caused by spending a lot of time indoors during childhood, rather than reading, as was once thought.
The practice of eating softer, processed foods has led to smaller jaws in humans, approximately 6% smaller than historically. This often results in dental malocclusions, where there isn't enough room for teeth, leading to issues like impacted wisdom teeth.
The age of puberty in women has decreased significantly (e.g., from 16 to 12.5 years in France over 200 years) due to increased energy availability in modern environments. This reflects the evolutionary drive to reproduce earlier when more energy is available.
Children today are less physically fit and have weaker skeletal structures than previous generations, contributing to rising rates of osteoporosis. Loading the skeleton through weight-bearing exercise during growth is essential for building strong bones and preventing bone loss later in life.
Chronic Stress, Inflammation, and Modern Medicine
Chronic psychosocial stress is a mismatch that elevates cortisol levels (stress hormone) persistently. High cortisol increases hunger (especially for sugar), promotes the storage of visceral fat (belly fat), and can suppress the immune system.
Excess visceral fat can lead to chronic systemic inflammation when fat cells become too large and dysfunctional, attracting immune cells and releasing inflammatory molecules (adipokines). This inflammation is linked to a wide range of mismatch diseases like diabetes, Alzheimer's, and heart disease.
Both low body fat and chronic stress can negatively impact fertility in women. The body interprets these conditions as unfavorable for reproduction and reduces investment in fertility.
Many forms of cancer are considered mismatch diseases, linked to high-energy environments (excess food, physical inactivity, high insulin levels), and carcinogens. Wealthier countries tend to have higher cancer rates. Modern patterns of reproduction, with fewer pregnancies and more menstrual cycles (due to birth control and smaller families), also contribute to higher rates of breast and ovarian cancers.
Modern medical systems often treat the symptoms of mismatch diseases rather than their underlying causes. This "dis-evolution" enables these diseases to remain prevalent and even worsen, leading to reduced quality of life, exorbitant healthcare costs, and disproportionately affecting low-income populations.
The hygiene hypothesis suggests that growing up in overly sanitized environments (without sufficient exposure to normal pathogens) leaves the immune system unchallenged, increasing the likelihood of allergies and autoimmune diseases as it "accidentally attack us".
Dieting and Skepticism
The ketogenic diet often leads to rapid short-term weight loss, primarily due to water loss, but data do not support its effectiveness as a long-term weight loss strategy. It involves using Ketone bodies as an alternative fuel source when carbohydrates (glucose) are avoided.
Fasting is a prolonged state of negative energy balance, which may trigger similar repair and maintenance mechanisms in the body as exercise. However, exercising is likely to provide more benefits than fasting alone.
It is advised to be skeptical of claims made by industries trying to sell products, especially those promising simple solutions to complex health problems, as there can be unintended consequences. For example, mouthwash can kill beneficial oral bacteria, and excessive sanitizing can negatively impact the microbiome.
Actionable Conclusions
To reduce the chances of developing mismatch diseases, one should strive to understand why these mismatches occur and use this knowledge to make informed decisions about diet, physical activity, and sitting habits. It's crucial to recognize that modern lifestyles are not "normal" from an evolutionary perspective.
Another key conclusion is to be aware of the vicious cycle where treating the symptoms of mismatch diseases (e.g., with medications or surgery) enables the underlying problems to persist or worsen, rather than addressing the root causes. Breaking this cycle involves preventing diseases in the first place.