62 pages • 2 hours read
The Story of the Human Body
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Part 2, Chapters 8-9Chapter Summaries & Analyses
Part 2: “Farming and the Industrial Revolution”
Part 2, Chapter 8 Summary: “Paradise Lost?”
Lieberman compares Adam and Eve’s expulsion from Eden to humans’ transition to agrarian lifestyles. Agriculture supports a larger population but has consequences, including overcrowding, disease, poor-quality diets, increased labor requirements, social strain, and an increased risk of starvation. Farming emerged in at least seven separate locations shortly after the end of the Ice Age. The Holocene, the current geological period, has warmer and more consistent weather; the favorable weather and the stress of feeding a growing population were the likely catalysts of agriculture.
Mediterranean archaeological sites show a population boom near the end of the Ice Age—a period called the Natufian. The Natufian was interrupted by the Younger Dryas, a return to Ice Age conditions 12,800 years ago. Some Natufians returned to nomadic lifestyles while others remained in their permanent settlements and practiced farming. Over 1,000 years, an agricultural economy emerged, and humans in the area domesticated several species, leading to a new period: The Pre-Pottery Neolithic A (PPNA), characterized by large settlements, mud-brick houses, stone food processing tools, and figuring and plaster art.
In Asia, rice and millet farming began around 9,000 years ago; in Mesoamerica, squash farming began 10,000 years ago followed by corn and other crops, which spread throughout the New World. African agriculture emerged around 6,500 years ago, and in New Guinea, farming practices started between 6,500 and 10,000 years ago. Humans also domesticated animals—dogs were domesticated 12,000 years ago, cattle 10,600 years ago, sheep and goats 10,500 years ago, pigs by 9,000 years ago, chickens 8,000 years ago, and llamas 5,000 years ago.
Agriculture spread quickly, largely replacing hunter-gatherer societies since it supported earlier weaning and larger populations; farmers and hunter-gatherers also formed positive relationships, fostering cultural exchanges. Children were viewed as useful laborers, and early agrarian lifestyles were likely pleasant. Most of the consequences emerged after it was too late to return to hunting and gathering.
Neolithic farmers had “monotonous” diets consisting mostly of grains and supplemented with produce, legumes, dairy, and meat. Limited diets can be grown in large quantities, and early farmers could produce 12,800 daily calories on average, meaning they could feed larger families. However, humans evolved to consume diverse diets, and mismatch diseases emerged as a result of the less- nutritious agrarian diets. By relying on limited foods, farmers were also more at risk of seasonal or disaster-caused food shortages, such as occurred in the Irish Potato Famine. Refining grains lowers their nutrient content, storing food can promote contamination, and high-starch diets can cause cavities and metabolic disorders.
Emergent farming cultures ate different foods but experienced similar side effects, including increased labor requirements for adults and children. The growing population density led to increases in infectious diseases and pests through trade, poor sanitation, alterations to the environment, and close contact with animals. Lieberman estimates there are over 100 mismatch diseases connected with the advent of agriculture.
Agriculture supported expanding population and resource surpluses, which allowed for intellectual progression. However, surpluses also led to social stratification, oppression and enslavement, famine, war, and mismatch diseases. Studies of height show that, in general, humans shrunk after the Agricultural Revolution—“probably because they were spending relatively more energy fighting infections, coping with occasional food shortages, and toiling for long hours in the fields” (204).
Only about 300 generations of farmers have existed in most areas, which is not enough time for significant biological evolution to occur but is enough time for genetic patterns to vary. Agriculture favored some genetic variations, like those that enhance the immune system, but such selection can have consequences: For instance, a mutation that protects against malaria can also cause sickle cell anemia. The effects of natural selection have been minor compared to the impacts of cultural evolution, and many facets of cultural evolution have been responses to the consequences of agriculture. Such responses are often cultural buffers that promote dysevolution.
Part 2, Chapter 9 Summary: “Modern Times, Modern Bodies”
Human lifestyles have undergone radical change since the beginning of the Industrial Revolution, which has created a health paradox: Human health has improved in some ways, but mismatch diseases have emerged, worsening health in other ways.
The Industrial Revolution began in the 1700s and is characterized by fossil-fuel powered manufacturing and distribution. It has allowed the population to grow by billions, and it has replaced human labor with machines and generalists with specialists. It has also enabled drastic scientific advancement that permeates culture. The three most significant cultural transitions of industrialization are the harnessing of energy, the reorganizing of social and economic institutions, and the growing importance of science. Lieberman writes: “It changed what we eat, how we chew, how we work, and how we walk and run, as well as how we keep cool and warm, give birth, get sick, mature, reproduce, grow old, and socialize” (214).
Before government and labor union interventions, work conditions in 19th-century factories were demanding, degrading, and dangerous, and industrialists worked much harder than farmers. Energetic requirements have decreased as technology has advanced. Industrialization has also reduced non-work physical activity levels; estimates show office workers expend 15% less energy each day than they did a few generations ago because of labor-saving advancements.
Diets, too, have drastically changed, and most people in developed nations rely on pre-made or pre-processed foods. Modern food manufacturers efficiently grow, produce, and distribute foods high in fat, salt, starch, and sugar, which humans evolved to crave because they are high in energy but rare in nature. Most foods are grown through industrial agriculture and supported by subsidies, and the prices of fatty and sugary foods have dropped while fruits, vegetables, and fish have become more expensive, relative to inflation. People also consume more daily calories. Industrial foods have environmental costs, with 10 calories of fossil fuels required to produce one calorie of food. Pesticides, herbicides, and fertilizers contaminate water and can poison workers, and increased meat consumption has led to extremely unsanitary and unhealthy farming operations. Most available foods are highly processed; this increases their starch and sugar and decreases their fiber content. Processed food takes less energy to digest, and the body is able to extract more nutrients; this causes sharp rises in blood-sugar levels for which the body is not adapted.
People in the early Industrial Revolution were subject to ineffective medicine and unsanitary conditions, particularly in cities, although many flocked to urban areas. Conditions improved as industrialization progressed, leading to the Enlightenment, which is associated with revolutions in medicine and sanitation. Sanitation and hygiene, spurred by necessity, prevented some infections, and, similarly, industrialism led to advancements in food storage and preservation, preventing foodborne illnesses.
Industrialism also led to changes in sleep patterns. Where hunter-gatherers slept in groups, took naps, and divided their nighttime sleep into two bouts of rest, post-industrialists slept in isolation, with limited naps and one shortened bout of rest at night. Modern humans sleep less for various reasons, including overstimulation, stress, and social and sensory deprivation. Over time, sleep deprivation has health and cognition consequences, and sleep deprivation is often correlated with low-income, resulting in a feedback loop.
Industrialization provided humans with more energy for growing and reproducing, and humans started growing larger, living longer, and having more babies. However, the rates of infants born underweight have risen, particularly among Black Americans. Changes to reproduction rates are more complex because having children became an economic burden, so people started using contraception. Decreased death rates have exacerbated population growth, and experts estimate the world population will reach 14 billion by 2100.
Poor individuals, especially in developing nations, experience fewer benefits and more consequences of modernity, and while younger individuals experience better health, older individuals’ health is declining. People live longer, but they die slower from noncommunicable diseases in a phenomenon called “extension of morbidity” (241). From some perspectives, extended morbidity is the price of modernity; however, Lieberman disagrees, citing the mismatch hypothesis. The Industrial Revolution solved some mismatch diseases created by the Agricultural Revolution, but it exacerbated and created others. Mismatch diseases are not inevitable, and people can live long, healthy lives under the right circumstances.
Part 2, Chapters 8-9 Analysis
Throughout Chapters 8 and 9, Lieberman stresses that cultural evolution takes place rapidly and drastically. In roughly 600 generations or less, humans transitioned from being nomadic hunter-gatherers, eating diverse diets, remaining active much of the day, and socializing with up to 230 people during their lifetime, to living in modern, crowded cities, eating processed foods, and rarely performing endurance activities. Through the depiction of the Agricultural and Industrial Revolutions, Lieberman develops the themes of Evolutionary Mismatches and Modern Disease and Evolutionary Implications for Health Policies and Practices. He imparts the underlying message that people are not responsible for becoming ill with mismatch diseases.
Evolutionary Mismatches and Modern Disease is addressed rather explicitly in Part 2. The mismatch hypothesis identifies a disparity between biological evolution—which is the focal point of Part 1—and cultural evolution. Discussing the impacts of cultural evolution and how they contribute to mismatch diseases is the main purpose of Chapters 8 and 9. Lieberman identifies several ways in which culture began to conflict with biology, such as the health consequences of monotonous diets that arose because humans are adapted to eat diverse diets. Through this, he implies that individuals aren’t responsible for developing mismatch diseases—culture is. This, in turn, implicitly develops Evolutionary Implications for Health Practices and Policies. If culture is responsible for mismatch diseases, then humans can change cultural practices and policies to prevent or more effectively mitigate such diseases. These ideas are introduced here but developed further in the final part of the book.
That people are not to blame for their diseases is further imparted through Lieberman’s use of personal anecdotes. In one instance, he shares that he enjoys cooking but that he does not have to use labor-intensive food preparation methods. This supports the idea that modern humans are suffering health consequences from labor-saving advancements. He also shares a parenting anecdote reflective of dietary changes:
I spent years as a parent trying to limit people’s efforts to serve these processed foods to my daughter. Instead of giving her an apple, she’d be given a fruit roll, a fruit-flavored candy ludicrously marketed as a substitute for fruit that has the same number of calories and vitamin C, but without the fiber or any other nutrients (223).
These anecdotes serve a dual purpose. First, they show how it is difficult to override cultural norms via well-informed personal lifestyle choices. Second, by including personal details, Lieberman presents himself and his experiences as relatable, attempting to create common ground with his audience. Both these effects combine to reinforce the idea that individuals are not responsible for mismatch diseases. If the expert writing the book cannot avoid the consequences of modernity, then the reader may be less likely to feel guilty or personally responsible for culturally accepted but unhealthy lifestyle choices. This prevents defensiveness, making the reader more likely to continue reading and to thoughtfully consider Lieberman’s perspective, which is critical to Lieberman’s goal of inspiring positive social change.
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