The Story of the Human Body

“If there was any one key initial adaptation, a spark that set the human lineage off on a separate evolutionary path from other apes, it was likely bipedalism, the ability to stand and walk on two feet.”

Evolution experts posit that bipedalism was the catalyst for the eventual development of humans. Bipedalism, as with other evolutionary traits, is a context-dependent adaptation. It made humans physically slower and weaker, but it provided other advantages, including making some foods easier to forage and allowing hominin species the use of their hands to carry food and tools. This passage reflects The Evolution of the Human Body and Health.

“It is impossible to ever know for sure why natural selection favored adaptations for bipedalism, but I think the evidence most strongly supports the idea that regularly standing and walking upright was initially selected to help the first hominins forage and obtain food more effectively in the face of major climate change that was occurring when the human and chimpanzee lineages diverged.”

Lieberman acknowledges that the fossil record of early hominins is limited; this reflects the difficulty of studying past events, particularly prehistoric events. However, he uses a broad perspective and multiple factors to draw plausible conclusions. His choice to directly address the limitations of the evidence displays academic integrity. The statement also implicitly provides insight into the future of the human species, by demonstrating that hominins have persevered through climate change in the past, and thus they may persevere through the current climate change.

“Just as the australopiths would not have evolved had not early hominins such as Sahelanthropus and Ardipithecus become bipeds of a sort, the genus Homo would not have evolved if Australopithecus had not become less arboreal, more habitually bipedal, and less dependent on fruit, setting the stage for subsequent evolution occasioned by yet more climate change.”

One reason that studying early hominins is important for understanding modern human biology and health is because evolution is an accumulative process. Lieberman devotes the first part of his text to discussing earlier hominins because many of the traits they evolved are visible in modern humans. The accumulative process of evolution is also reflected in the sequential structure of Part 1, in which Lieberman discusses hominins in order from oldest to most recent.

“Are you worried about rapid global climate change today? If not, you should be, because rising temperatures, altered rainfall patterns, and the ecological shifts they cause imperil our food supply.”

The pivotal word in Lieberman’s assertion about climate change is “rapid.” In his discussion on human evolution, Lieberman acknowledges the importance of climate change in shaping species’ evolutionary trajectories. However, he does not support apathy regarding modern climate change. The current climate change is occurring at a much faster rate than other historic climate changes, and it is being caused by human activity. Modern climate change is also accompanied by severe global environmental degradation, which can lead to severe food shortages.

“Barring the invention of time travel or the discovery of a relict species of early Homo on some as-yet uncharted island, we must piece together a picture of how the first members of the human genus eked out a living by studying their fossils and the artifacts they left behind in conjunction with what we know about how hunter-gatherers live today.”

Lieberman uses absurd examples of time travel and the discovery of a new island to comically emphasize the limitations of studying the lifestyles of Homo erectus and other early hominins. While Lieberman admits that studying such early lifestyles necessarily involves speculation, he also asserts that physical evidence, such as food and tool remnants, informs these conjectures, making them more reliable.

“A pregnant human mother caring for a three-year-old plus a seven-year-old needs about 4,500 calories a day to feed herself plus her fetus and children. If her kids had chimp-sized brains, then she’d need approximately 450 fewer calories each day—no small quantity in the Paleolithic.”

Lieberman employs several techniques to make his discussions more relatable. Here, he creates a realistic scenario—a pregnant mother caring for herself and two children—and he incorporates specific numerical data and a comparison to chimpanzees. These remarks provide foundational information for his later discussion on Evolutionary Implications for Health Practices and Policies.

“Were you a hunter-gatherer, you wouldn’t have to work any more than necessary to satisfy your family and group’s daily needs. After that, you would benefit from resting and devoting time to social activities such as gossiping and enjoying the company of family and friends.”

Modern lifestyles are vastly different from the lifestyles of hunter-gatherers. By describing how hunter-gatherers have more free time, Lieberman implies that modern demands are, in some ways, more stressful than the demands of hunter-gatherer lifestyles. This disparity helps provide the framework for the later discussions on Evolutionary Mismatches and Modern Disease.

“Put differently, not all evolution occurs through natural selection, and interactions between genes and the environment have been changing rapidly, sometimes radically, primarily because of changes in our bodies’ environments caused by rapid cultural evolution.”

Lieberman’s discussion on the interactions between the environment and genetic expression alludes to the concept of epigenetics. Epigenetics is a branch of science which studies how environmental and behavioral factors impact genetic expression. Some genes require certain environmental stimuli before they are expressed: For instance, a person who eats a typical Western diet is more likely to experience type 2 diabetes.

“I don’t think it is possible to overemphasize just how important mismatch diseases are. You are most likely going to die from a mismatch disease. You are most likely to suffer from disabilities caused by mismatch diseases. Mismatch diseases contribute to the bulk of health-care spending throughout the world.”

Personal pronouns increase the tension of Lieberman’s assertions. By directly addressing the reader (“you”), Lieberman creates an immersive experience to invite the reader to feel personally involved with the material. It also suggests that one of Lieberman’s primary goals is to inform individuals so that they can make knowledgeable and healthful decisions to address Evolutionary Mismatches and Modern Disease.

“Ever since this transition, which began about six hundred generations ago, the human species’ punishment has been to toil miserably as farmers, growing our daily bread rather than plucking luscious fruits just there for the taking. In a rare instance of accord, creationists and evolutionary biologists agree that it has been downhill for humans ever since.”

Lieberman here merges a common juxtaposition—creationism versus evolution—demonstrating how both the Christian and scientific perspectives have recognized that agriculture has had negative impacts on well-being. While the transition to agriculture supplied humans with food surpluses and allowed their populations to drastically expand, the transition also increased human labor requirements, lowered humans’ diet qualities, introduced class systems, inequality, and increased the prevalence of both infectious and noninfectious diseases.

“Cavities, I should add, were hardly a trivial concern before the invention of antibiotics and modern dental care.”

Although cavities are considered a relatively minor health concern in the modern world, they were potentially fatal for humans living in the Neolithic. By incorporating statements such as this, Lieberman portrays a more accurate depiction of Neolithic life. Such statements also draw attention to modern amenities or practices which many readers may take for granted.

“For the first time in millennia, people in developed nations rarely, if ever, worry about epidemics or succumbing to contagion. Perhaps this complacency is misguided.”

The Story of the Human Body was published in 2014, six years before the 2020 COVID-19 pandemic. Here, the author draws attention to how advancements in modern science and public hygiene have led to many health benefits for humans, even though such changes have also resulted in Evolutionary Mismatches and Modern Disease in other respects.

“In short, the Industrial Revolution was actually a combination of technological, economic, scientific, and social transformations that rapidly and radically altered the course of history and reconfigured the face of the planet in less than ten generations—a true blink of an eye by the standards of evolutionary time.”

Lieberman stresses the rapidity and extent of the Industrial Revolution directly, then re-emphasizes the point by ending with a metaphor. This repetition reflects the importance of the concept, and it suggests that Lieberman assumes many readers likely take post-industrial lifestyles and amenities for granted. By drawing attention to how recent industrialization is, Lieberman also reinforces the idea that humans are not adapted for living in modern developed environments.

“In much of the developed world, the food we eat is now as industrial as the cars we drive and the clothes we wear.”

By comparing food to clothes and cars, Lieberman implies that modern processed foods are unhealthy. It also reinforces his earlier remark that the dietary transitions following the Industrial Revolution are more significant and impactful than the transitions following the Agricultural Revolution.

“By the year 2015, there will be more people over the age of sixty-five than under the age of five, yet nearly half of those above the age of fifty will be in some state of pain, disability, or incapacity that requires medical care.”

This remark is intentionally misleading. It implies that pain, disability, and incapacity are inherent consequences of modernity, but Lieberman rejects this idea, blaming the mismatch hypothesis for many of the health problems often experienced as a person ages. If mismatch diseases and their causes are identified, people can prevent pain, illness, and disability later in life, reflecting Evolutionary Implications for Health Practices and Policies.

“Stepping back from the details, the bottom line is that your body functions like a fuel bank, storing energy after you eat food and withdrawing energy for use during times of need.”

After explaining the processes of digestion and energy storage and release in scientific detail, Lieberman includes a synthesis of the main points. By including the detailed description with in-text citations, Lieberman enhances his academic credibility, and by including a synopsis, he ensures layman readers understand the critical points.

“Because of industrialization, the cheapest and most abundant foods are low in fiber and rich in simple carbohydrates and sugar, especially high fructose corn syrup—all of which promote obesity, especially visceral obesity, hence insulin resistance.”

Lieberman implies that cultural evolution has caused the increasing rates of obesity and type 2 diabetes. Lieberman stresses that type 2 diabetes is usually preventable, then transitions into examining why maintaining healthy diets and exercise routines is so difficult. By structuring the discussion in this way, Lieberman avoids blaming individuals for developing type 2 diabetes while still stressing that the disease is preventable.

“If you don’t load your skeleton when you are young, it will never grow to be strong, and if you don’t stimulate your brain sufficiently as you age, you are at risk of losing cognitive function more rapidly, potentially leading to diseases like dementia.”

Lieberman invokes the “use it or lose it” adage in his discussion of physical activity. He uses ominous direct statements to identify consequences of inactivity, and he emphasizes his point through stressing that health is time-sensitive. However, his statement also implies the hopeful message that people have the power to prevent mismatch diseases by making healthy decisions.

“The bottom line is that your jaws and teeth grow and fit together through many processes that involve more than just chewing forces, but a certain level of munching and crunching is necessary for the system to work properly.”

The author’s linguistic choices impact both the function and tone of this statement. The phrase “bottom line” signals that the statement is a summary of the main points. The rhyming pair “munching and crunching” adds a conversational tone, and the use of “your” invites the reader in and creates a more immersive reading experience. Creating an immersive and enjoyable reading experience is important for maintaining the readers’ interest when writing technical texts for layman audiences.

“And why do we permit companies to pollute our air, water, and food with chemicals known to contribute to illness and death?”

The series of rhetorical questions Lieberman uses to discuss the various ways humans willingly use toxic chemicals invites readers to question these harmful practices, reflecting Evolutionary Implications for Health Practices and Policies. The rhetorical questions also have a sarcastic undertone, implying that the use of such toxins is absurd.

“Don’t worry! I am not going to make you feel bad about sitting in chairs, and, for the record, I have no intention of getting rid of the chairs in my house.”

Many of Lieberman’s discussions may inspire the reader to feel guilt, regret, or shame for practicing behaviors that contribute to mismatch diseases. Lieberman recognizes this by addressing the reader’s potential concern directly. He also implies that humans should not simply give up functional modern amenities, but instead adopt healthy practices that can help mitigate mismatch diseases.

“Because of farming, industrialization, sanitation, new technologies, improved social institutions, and other cultural developments, we have more food, more energy, less work, and additional blessings that immeasurably enrich and improve our existence.”

Although The Story of the Human Body focuses on the ways that modernity causes mismatch diseases, Lieberman also addresses the benefits of modern lifestyles. He does not suggest, like some primitivists, that humans should turn back cultural evolution and resume hunter-gatherer lifestyles; instead, he stresses that evolutionary medicine can provide methods to prevent or mitigate mismatch diseases, thereby improving the overall quality of life for humans.

“Because it costs an extra $18,000 a year to treat an American with heart disease, one can estimate that persuading just 25 percent more of the population to become fit could save in excess of $58 billion per year for just heart disease care alone.”

Along with having physical and mental costs, mismatch diseases also have high economic costs. This information may help encourage readers who are more financially motivated to take steps to prevent mismatch diseases, adding another angle to the discussion of Evolutionary Implications for Health Practices and Policies.