Book Summary: “The Story of the Human Body” by Daniel E. Lieberman

“The Story of the Human Body” by Daniel E. Lieberman

Title: The Story of the Human Body: Evolution, Health and Disease
Author: Daniel E. Lieberman
Scope: 3 stars
Readability: 4 stars
My personal rating: 5 stars
See more on my book rating system.

If you enjoy this summary, please support the author by buying the book.

Topic of Book

Liebermann explores the genetic history of the human body, and how genetics still plays a role in human history.

If you would like to learn more about how biology has affected human history, read my book From Poverty to Progress: How Humans Invented Progress, and How We Can Keep It Going.

Key Take-aways

  • The common assumption that humans stopped evolving biologically since the advent of civilization is false.
  • The human body has undergone significant genetic change.
  • The domain of disease and resistance to disease is one of the most important changes.
  • Key biological adaptation among early humans include:
    • Bipedalism
    • Enlargement of the brain,
    • Shift of diet away from fruits and to meat and grains
    • Highly efficient sweat glands to increase endurance beyond most mammals
  • Many of today’s most common diseases are “mismatch diseases” that originated with the development of agriculture:
    • Smallpox
    • Polio
    • Plague
  • Other mismatch diseases arise from the modern lifestyle:
    • Diabetes
    • Obesity
    • Heart disease

Important Quotes from Book

Yet, despite much controversy and passionate ignorance, the idea that evolution occurs should not be contentious. Evolution is simply change over time. Even die-hard creationists recognize that the earth and its species have not always been the same.

Natural selection is a remarkably simple process that is essentially the outcome of three common phenomena. The first is variation: every organism differs from other members of its species. Your family, your neighbors, and other humans vary widely in weight, leg length, nose shape, personality, and so on. The second phenomenon is genetic heritability: some of the variations present in every population are inherited because parents pass their genes on to their offspring. Your height is much more heritable than your personality, and which language you speak has no genetically heritable basis at all. The third and final phenomenon is differential reproductive success: all organisms, including humans, differ in how many offspring they produce who, themselves, survive to reproduce. Often, differences in reproductive success seem small and inconsequential (my brother has one more child than I do), but these differences can be dramatic and significant when individuals have to struggle or compete to survive and reproduce.

If you agree that variation, heritability, and differential reproductive success occur, then you must accept that natural selection occurs, because the inevitable outcome of these combined phenomena is natural selection. Like it or not, natural selection just happens. Stated formally, natural selection occurs whenever individuals with heritable variations differ in the number of surviving offspring they have compared to other individuals in the population (in other words, they differ in their relative fitness).

Natural selection rarely, if ever, achieves perfection because environments are always changing.

Perfection may be unattainable, but bodies function remarkably well under a wide range of circumstances because  of the way evolution accumulates adaptations in bodies much like the way you probably keep accumulating new kitchen utensils, books, or items of clothing. Your body is a jumble of adaptations that accrued over millions of years. 

The final and most important point about adaptation is really a crucial caveat: no organism is primarily adapted to be healthy, long-lived, happy, or to achieve many other goals for which people strive. As a reminder, adaptations are features shaped by natural selection that promote relative reproductive success (fitness). Consequently, adaptations evolve to promote health, longevity, and happiness only insofar as these qualities benefit an individual’s ability to have more surviving offspring.

“Nothing in biology makes sense except in the light of evolution.” Why? Because life is most essentially the process by which living things use energy to make more living things.

The fundamental answer to why so many humans are now getting sick from previously rare illnesses is that many of the body’s features were adaptive in the environments for which we evolved but have become maladaptive in the modern environments we have now created. This idea, known as the mismatch hypothesis, is the core of the new, emerging field of evolutionary medicine, which applies evolutionary biology to health and disease. 

Before our ancestors were hunter-gatherers they were apelike bipeds, and before then they were monkeys, small mammals, and so on. And since then, some populations have evolved new adaptations to being farmers. Consequently, there was no single environment for which the human body evolved, and hence is adapted. Thus, to answer the question “What are we adapted for?” requires that we consider not just hunter-gatherers realistically, but also look at the long chain of events that led to the evolution of hunting and gathering, as well as what happened since we started to farm our food.

I don’t think it is possible to overemphasize just how important mismatch diseases are. You are most likely going to die from a mis-match 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.

The story of the human body can be boiled down to five major transformations. None of them were inevitable, but each altered our ancestors’ bodies in different ways by adding new adaptations and by removing others.

TRANSITION ONE: The very earliest human ancestors diverged from the apes and evolved to be upright bipeds.

TRANSITION TWO: The descendants of these first ancestors, the australopiths, evolved adaptations to forage for and eat a  wide range of foods other than mostly fruit.

TRANSITION THREE: About 2 million years ago, the earliest members of the human genus evolved nearly (though not completely) modern human bodies and slightly bigger brains that enabled them to become the first hunter-gatherers.

TRANSITION FOUR: As archaic human hunter-gatherers flourished and spread across much of the Old World, they evolved even bigger brains and larger, more slowly growing bodies.

TRANSITION FIVE: Modern humans evolved special capacities for language, culture, and cooperation that allowed us to disperse rapidly across the globe and to become the sole surviving species of human on the planet.

Contrary to what some people assume, the human body didn’t stop evolving once the Paleolithic ended. Instead, natural selection is still relentlessly chugging along.

Two cultural transformations have been of vital importance to the human body and need to be added to the list of evolutionary transformations above:

TRANSITION SIX: The Agricultural Revolution, when people started to farm their food instead of hunt and gather.

TRANSITION SEVEN: The Industrial Revolution, which started as we began to use machines to replace human work. 

Although these last two transformations did not generate new species, it is difficult to exaggerate their importance for the story of the human body because they radically altered what we eat and how we work, sleep, regulate our body temperature, interact, and even defecate. 

We can better understand why more people are getting chronic noninfectious mismatch diseases and how to prevent these illnesses by considering interactions between cultural evolution and our inherited, still-evolving bodies. These interactions sometimes set in motion an unfortunate dynamic that typically works as follows: First, we get sick from noninfectious mismatch diseases caused by our bodies being poorly or inadequately adapted to the novel environments we have created through culture. Then, for various reasons, we sometimes fail to prevent these mismatch diseases. 

In all cases, however, by not addressing the novel environmental causes of mismatch diseases we permit a vicious circle to occur that allows the disease to remain prevalent or sometimes to become more common or severe. This feedback loop is not a form of biological evolution because we don’t pass on mismatch diseases directly to our children. Instead it is a form of cultural evolution because we pass on the environments and behaviors that cause them.

New technologies that rapidly and inexpensively sequence entire genomes have revealed hundreds of genes that have been under strong selection during the last few thousand years within particular populations. As you might expect, many of these genes regulate reproduction or the immune system… Others play a role in metabolism and helped certain farming populations adapt to foods such as dairy products and starchy staple crops. A few selected genes are involved in thermoregulation.

Not all evolution occurs through natural selection. An even more powerful and rapid force today is cultural evolution, which has altered many crucial interactions between genes and the environment by altering environments, not genes. 

As innovation has accelerated, especially since farming began, we have devised or adopted a growing list of novel cultural practices that have had conflicting effects on our bodies. 

I don’t think it is possible to overemphasize just how important mismatch diseases are. You are most likely going to die from a mis-match 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.   

Broadly speaking, most mismatch diseases occur when a common stimulus either increases or decreases beyond levels for which the body is adapted, or when the stimulus is entirely novel and the body is not adapted for it at all. Put simply, mismatches are caused by stimuli that are too much, too little, or too new. 

Of the processes that alter environments to cause evolutionary mismatches, the most common and powerful occur because of cultural evolution. 

“What followed the Paleolithic—farming, industrialization, and other forms of “progress”—may have been a boon to the average person, but they promoted new diseases and other problems that were rare or absent during the Paleolithic. Almost every major infectious epidemic, such as smallpox, polio, and the plague, happened after the Agricultural Revolution began.”

“cultural evolution hasn’t halted natural selection, and it has not only driven but sometimes even accelerated selection. As we will see, the Agricultural Revolution has been an especially powerful force for evolutionary change.”

A typical adult hunter-gatherer female will manage to collect about 2,000 calories a day, and a male can hunt and gather between 3,000 and 6,000 calories in a day. A hunter-gatherer group’s combined efforts yield just about enough food to feed small families. In contrast, a household of early Neolithic farmers from Europe using solely manual labor before the invention of the plow could produce an average of 12,800 calories per day over the course of a year, enough food to feed families of six. In other words, the first farmers could double their family size. 

One of the biggest problems is a loss of nutritional variety and quality… farmers sacrifice quality and diversity for quantity by focusing their efforts on just a few staple crops with high yields.

Unlike hunter-gatherers, farmers are susceptible to diseases such as scurvy (from insufficient vitamin C), pellagra (from insufficient vitamin B3), beriberi (from insufficient   vitamin B1), goiter (from insufficient iodine), and anemia (from insufficient iron). Relying heavily on a few crops—sometimes just one crop—has other serious disadvantages, the biggest being the potential for periodic food shortages and famine.   

Another risk of long-term food storage is contamination. 

An additional and very significant health problem caused by farmers’ diets is due to lots of starch. Hunter-gatherers eat plenty of complex carbohydrates, but farmers grow and then process cereals, roots, and other plants that are rich in simple carbohydrates, also known as starch. Starch tastes great, but too much can cause a raft of mismatch diseases. The most common of these maladies is rotten teeth.

 Epidemics could not exist prior to the Neolithic because hunter-gatherer population densities are below one person per square kilometer, which is beneath the threshold necessary for virulent diseases to spread. 

Another insalubrious by-product of farming that promoted infectious mismatch diseases is poor sanitation. Hunter-gatherers who live in small temporary camps simply head off into the bushes to defecate, and they produce only modest amounts of refuse. As soon as people settle down permanently, they inevitably accumulate lots of waste and foul their nests. Permanent latrines contaminate drinking water and soil with human fecal matter, refuse piles up and rots, and dwellings create an ideal environment for small animals… These pests sometimes reciprocate our hospitality by being vectors of disease. 

Most egregiously, when farmers clear vegetation and irrigate crops, they create ideal habitats for mosquitoes.

Finally, humans have unleashed upon ourselves a frightening array of horrid diseases—more than fifty—that we acquired by living in close contact with animals. These diseases are some of the scariest, nastiest pathogens that pose a serious risk to humans, including tuberculosis, measles, and diphtheria (from cattle); leprosy (from water buffalo); influenza (from pigs and ducks); and plague, typhus, and possibly smallpox (from rats and mice). 

 All told, there are probably more than one hundred infectious mismatch diseases that were caused or exacerbated by the origin of agriculture.

Analyses of people’s height suggest that the initial stages of farming were initially beneficial for people’s health in many, though not all, parts of the world… over its first few thousand years, people’s stature initially increased by about 4 centimeters (1.5 inches) in males and a little less in females. However, stature then started to decline beginning around 7,500 years ago at the same time that skeletal markers of disease and nutritional stress also become more common.   

Simply put, over time, farming life generally became nastier, more brutish, shorter, and more painful. 

Farming clearly boosted rates of evolution, because, as populations have exploded in size (by more than a thousandfold), each generation has made available many new mutations upon which selection can act. Efforts to measure this surge in diversity have identified more than one million new genetic variations that arose in various populations across the planet in the last few hundred generations. 

Studies have identified more than one hundred genes that have been favored by recent natural selection, many because of farming. 

  1. “The 10,000 Year Explosion: How Civilization Accelerated Human Evolution” by Cochran and Harpending
  2. “Who We Are and How We Got Here” by David Reich
  3. “The Gap: Science of What Separates Us from Animals” by Thomas Suddendorf
  4. “Is There Anything Good About Men?” by Roy F. Baumeister
  5. “A Farewell to Alms: A Brief Economic History of the World” by Gregory Clark
  6. “The Son Also Rises: Surnames and the History of Social Mobility” by Gregory Clark
  7. “Meta-analysis of … twin studies” by many

If you would like to learn more about how biology has affected human history, read my book From Poverty to Progress: How Humans Invented Progress, and How We Can Keep It Going.

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