Survival of the Fitter

In this final chapter, Lieberman summarizes his conclusions, and lists potential solutions to the problem of mismatch diseases.  The first solution is to let natural selection sort everything out.  Although this is a heartless solution, Lieberman admits that natural selection continues to act on the human population.  However, natural selection is unlike to act on mismatch diseases that occur later in life, because they often have no effect on reproduction.  The second solution is to invest more in biomedical research and treatment.  Lieberman supports increasing biomedical research, but warns that there likely will be no large breakthrough, but only small incremental progress.  Additionally, drug treatments usually do not cure chronic diseases, and can cause unpleasant side effects.  It is also difficult to target the cause of chronic diseases, and instead symptoms are treated.  Lieberman maintains that one of the best ways to prevent mismatch diseases are to eat healthy and exercise.  This leads to the third solution, which is to educate and empower.  People should learn how their bodies work, and how to prevent chronic mismatch diseases.  Lieberman points out that advertisers commonly market tasty and unhealthy food, but there are very few messages about proper nutrition and exercise.  The fourth solution is to change the environment.  The logic is that sometimes humans need external forces to force change.  Examples of this are to require physical exercise in schools or ban fast food from school cafeterias.  When in comes to adults, the government cannot ban unhealthy food, but it discourage consumption of soda and fast food with taxes.  The government could also require warnings similar to ones on cigarettes currently.  As a final message, Lieberman reminds us that “Nothing in biology makes sense except in the light of evolution”.  He reminds us that human evolution was not a triumph of brains over brawn, and that we cannot fix problems with our biology.  Instead of waiting for scientists to cure diabetes or heart disease, we should pay attention to our body, and attempt to prevent chronic illnesses with nutrition and exercise.

The Hidden Dangers of Novelty and Comfort

In this chapter, Lieberman discusses the evolutionary reasons behind our reasoning in cost benefit analyses.  We willingly engage in potentially harmful behaviors because they have benefits short term, but may have consequences in the long term.  Examples of this include smoking, tanning booths, and pollution.  Lieberman suggests that this behavior occurs because we fail to see the novelty of our situation.  For us, it is normal to live the way we do, and therefore, we overlook potentially dangerous behaviors.  Lieberman suggests that a second factor is that humans believe that if something is comfortable it must be good for us.  One example of this is the belief that wearing comfortable shoes is necessary, when in fact, shoes are a very recent development in our history.  Lieberman argues that shoes help prevent injury from running with bad form, but even with shoes running long distances in this manner will result in injury.  When running barefoot, humans are unable to run with bad form, because it will hurt.  Lieberman argues that both are good options, but that barefoot running will not allow for bad form.  However, one shoe related injury, called plantar fasciitis, which occurs when the muscles of the foot arch become weak.  Doctors usually treat the symptoms, which includes shoes with arch support, which relieve the symptoms but only increases the problem of weak arch muscles.  Lieberman argues that when a person suffers from a repetitive stress injury, the cause should to treated instead of just relieving the symptoms.  Lieberman argues that myopia, or nearsightedness is another mismatch disease.  In fast, evidence shows that only 3% of hunter gatherers are nearsighted, and that only the upper class in early European society suffered from nearsightedness.  It’s been theorized that if a child persistently stares at close objects, it will lengthen the eyeball’s walls, causing myopia.  However, this hypothesis is controversial, and has only been tested in animals.  Another hypothesis is that the invention of glasses has allowed for the selection of bigger brains, which causes myopia.  But Lieberman is quick to discredit this theory, stating that brain size has actually decreased since the Ice Age.  Either way, someone can be predisposed for myopia, but it is the environmental factors that cause myopia.


In this chapter, Lieberman explains how the body is able to adapt to the environment.  The ability of the body to respond to environmental factors is called phenotypic plasticity, and some examples of this include tanning in the summer and gaining thicker bones with exercise.  However, if humans move to a different environment, these adaptations can become mismatched.  Additionally, the body requires stresses, such as exercise or sunlight to gain these adaptations.  This “use it or lose it” situation can create mismatch if the necessary amount of stress is not met.  One example of this is osteoporosis.  Bones require regular exercise to cause small deformations, which heal and cause the bone to grow back stronger.  Osteoporosis can occur in the absence of regular exercise and calcium deficiencies.  Another mismatch is wisdom teeth that do not fit in the jaw.  Lieberman explains that farmers often had awful teeth with cavities, and 25% of them with impacted wisdom teeth.  However, hunter gatherers have no problems with impacted teeth.  Lieberman suggests that during childhood, repeated chewing on tough foods is necessary to align the teeth correctly and strengthen the jaw.  However, foods today do not require strenuous chewing, so modern humans must rely on orthodontists and oral surgeons to fix the resulting dental problems.  Additionally, Lieberman explains that early exposure to microbes is important to stress the immune system properly.  If this does not occur, humans are more at risk for allergies and autoimmune diseases.  Lieberman suggests that it is important to learn the cause of mismatch disease such as allergies, to treat the source of the problem.  He explains that all of these diseases are a result of dysevolution, where we treat the symptoms but not the cause.  He argues that many mismatch diseases can be prevented with regular exercise and a healthy diet.

The Vicious Cycle of Too Much

In this chapter, Lieberman argues that obesity due to overabundance of energy is the largest problem in the US currently.  Type 2 diabetes and heart disease are mismatch diseases related to obesity.  Once food is eaten, the excess energy is stored to fuel the body later on.  Humans are able to endure long periods of negative energy balance by relying on these fat stores, and until recently, humans went long periods with negative energy balances.  Lieberman explains that humans are adapted to store a lot of fat, because our large brains require a constant flow of sugar to the brain.  Compared to other primates, humans store way more fat in the body.  Lieberman explains the thrifty phenotype hypothesis, which suggest that if a pregnant woman is not getting enough nutrients, the baby will be predisposed to store fat in preparation for an environment with limited resources.  However, this does not explain why children born to healthy or overweight women also develop obesity.  Lieberman explains that the reasons why some people store more fat that others is not known.  It is important for more research on the subject, especially because the numbers of people who are obese are rising.  Although people are eating more than they ever have, Lieberman explains that another reason for increased obesity is the types of food that are eaten.  Insulin rises when blood sugar levels rise, and allows fat cells to store the sugar as fat.  Insulin rises when glucose is eaten, and current processed food is high in glucose, and low in fiber, which slows the rate of digestion and increases satiation.  Additionally, fructose is processed by the liver, and without fiber, an abundance of fructose can overwhelm the liver.  Hunter gatherers would only be able to acquire such large amounts of sugar in honey, so our digestive system is simply not adapted to process large amounts of sugar.  Additionally, Lieberman explains that exercise alone is not a good way to lose weight, because it burns relatively few calories and then stimulates hormones to make you hungry.  Additionally, it is difficult to lose weight because someone must be in a negative energy state, which increases hunger.  Type 2 diabetes is also a chronic mismatch disease that results in insulin resistance.  Excess visceral fat, or fat around the internal organs, is a risk factor for type 2 diabetes.  However, losing this visceral fat is able to even reverse the early stages of type 2 diabetes.   But Lieberman explains that the problem is people wait until they are seeing symptoms before making changes, when it would be more effective to make changes earlier.  Another chronic mismatch disease is heart disease, which results from high LDL cholesterol.  It is common because of the same factors that cause diabetes: inactivity, poor diet, and obesity.  This disease can also be mitigated by regular exercise and a good diet.  Lieberman points out that just being overweight is not a guarantee of a problem, instead better predictors of health are where you store fat, how you eat, and how much you exercise.

Modern Times, Modern Bodies

In this chapter, Lieberman covers the changes due to industrialization, and the rapid changes in the past 250 years.  The Industrial Revolution occurred when humans started using fossil fuels to power technology.  In the span of only 12 generations, humans went from doing a wide range of manual work to primarily highly specialized office work.  The Industrial Revolution coincided with an increase in science, which increased knowledge of biology and medicine.  Initially, factory work was just as strenuous as farming.  But as technology increased, and robots took over strenuous tasks, office work began to take over.  Lieberman argues that industrialization profoundly decreased the amount of physical exercise humans get.  Our jobs are no more taxing than sitting down, and the cost of traveling has been reduced by elevators, cars, and planes.  Washing machines and dishwashers have reduced the energy spent on cleaning, and air conditioning and heating has reduced the amount of energy spent on body temperature.  Additionally, industrialization has fundamentally changed our diet.  Large corporations took over small scale farming, and food producers are able to produce cheap, high calorie food.  Most food eaten in the US today is grown industrially, and quantities are high and prices are low.  However, Lieberman explains that industrial food production takes a toll on the environment and the health of the workers.  Although quantity of food increased because of industrialization, the quality decreased, leading to increased obesity in the population.  Lieberman also explains how industrialization increased scientific knowledge, and improved urban conditions with knowledge of sanitation and medicine.  One of the main advances was the discovery of bacteria and viruses, and the invention of vaccines.  Advances in sanitation and plumbing also reduced the burden of disease, and allowed society to combat disease.  All of these changes have resulted in a society with abundant food and less of a requirement of physical activity.  Humans are expected to live longer, but die slower of chronic illnesses.   Lieberman explains that the Industrial Revolution was successful at solving mismatch diseases from the Agricultural Revolution, but created a whole host of new, chronic, mismatch diseases.

Paradise Lost?

In this chapter, Lieberman explains the evolutionary consequences of farming.  After the end of the Ice Age, when the climate was more temperate, farming emerged in many different places around the world.  At first, early farmers supplemented their diet with hunting, but they eventually learned to domesticate animals for food.  Quickly, farming became the dominant strategy, with only a few groups of hunter-gatherers left.  Lieberman explains that the likely cause of this was the ability of farmers to grow more food, and therefore support more children.  In fact, for farmers, children are an asset, because they can help work.  However, although farming generated more food, it was less nutritious and less varied which results in nutrient deficiencies and mismatch diseases.  Additionally, if crops fail, farmers are at risk for severe famines, something that never occurred with hunter-gatherers.  Lieberman explains that farming required much more work than hunting and gathering, and required more power and less endurance.  However, Lieberman explains that one of the consequences of farming is the increased population size, and therefore increased infectious disease.  Farming also allows for permanent settlements and increased population density, which also increases infectious disease.  Farming also requires trading, which exposes people to new infections.  Lieberman explains that hunter-gatherer societies likely suffered from parasites, vector borne diseases, and zoonotic diseases, but did not suffer from large scale human to human transmitted epidemics.  Additionally, farmers suffered from poor sanitation, which only increased their risk of disease and allowed rodents and fleas to spread illness.  In fact, rats and mice quickly evolved to take advantage of farmers.  Living with animals also increased farmers’ risk of zoonotic diseases, and irrigation from crops created ideal environments for mosquitoes.  Lieberman estimates that over 100 mismatch diseases were caused by the Agricultural Revolution, and although technology is advanced, we are still vulnerable to new epidemics.  Lieberman says that because of technology, society rarely worries about epidemics currently, but he warns that “perhaps this complacency is misguided”, as the population is larger and denser than it even has been.  In these current times, I feel as though this particular statement is very relevant.  Even though farming exposed the human population to infectious disease, humans have evolved resistance to many diseases, including malaria, and have evolved mutations to help humans adapt to domestication.  Additionally, cultural improvements, such as farming tools have improved the lives of farmers.  Clearly, early farmers suffered from mismatch diseases, and have developed ways to mitigate the symptoms of these problems.

Progress, Mismatch, and Dysevolution

In this chapter, Lieberman debates the merits of living like a Paleolithic hunter-gatherer.  He explains that currently, there are unprecedented numbers of people able to live long and healthy lives, which is an improvement from even the last 100 years.  Conversely, farming and industrialization has promoted both infectious and noninfectious diseases, as well as famines and malnutrition.  Lieberman argues that while farming created more food and allowed populations to flourish, it also caused the farmer to work harder, experience worse health, and die younger.  Lieberman asks, are some forms of ill health a necessary consequence of civilization?  Despite modern assumptions, Lieberman argues that cultural evolution hasn’t halted natural selection, but instead, has accelerated it.  Additionally, cultural evolution is moving at a fast pace as well, and while this is not directly heritable, we can pass environmental changes on to our children.  He argues that new chronic conditions are not from new genes, but from how genes interact with a new environment.  Lieberman gives examples of type 2 diabetes, myopia, and flat feet, which are all current problems, but ones that our ancestors certainly did not suffer from.  He argues that it is essential for doctors to learn the evolutionary reasons behind chronic conditions, so that they can be treated from the source.  Additionally, it is important to understand evolution to predict how infectious diseases and antibiotic resistant bacteria will respond.  Lieberman also argues that many symptoms of illness, such as fever, may actually be adaptations, and it is important to understand the body’s reason for the way it is reacting.  He introduces the idea of evolutionary mismatch, where genes that are advantageous in one environment are detrimental in another.  Mismatches are caused by some environmental stimulus that is too much or too little, such as too much fat in the diet or too little sunlight.  This is not a new problem, and Lieberman explains that mismatch likely occurred as Homo sapiens migrated out of Africa.  Understand mismatch diseases is complicated and difficult, especially because it is difficult to determine what exactly humans are adapted for.  Additionally, Lieberman makes the point that just because something is different, doesn’t mean that it is bad.  For example, brushing your teeth is a modern idea, but it is unquestionably helpful.  Another problem is that it is difficult to tell if a disease is a result of a mismatch if possible environmental causes are unknown.  Lieberman also introduces the idea of dysevolution, which is a form of cultural evolution where the symptoms of a mismatch disease are treated, but not the cause.  One example of this is cavities, which are treated with dentists, and not by removing the sugar from our diet, which is the underlying cause.  Lieberman emphasizes that mismatch diseases and their causes must be understood fully to treat the true cause.

A Very Cultured Species

This chapter deals with the question of why Homo sapiens are the only Homo species left.  Homo sapiens evolved in Africa about 200,000 years ago, and started to migrate out of Africa between 100,000 and 80,000 years ago.  However, modern humans descended from a relatively small group of only 14,000 individuals.  This resulted in a current population that is very genetically similar.  Additionally, from fragments of DNA extracted from Neanderthal fossils, it was discovered that 2-5% of the human genome is from Neanderthals.  As Homo sapiens moved out of Africa, they settled in every continent except for Antarctica.  And at the same time, Homo erectus and Neanderthal populations went extinct.  What makes Homo sapiens different?  Lieberman argues that Homo sapiens were better able to invent tools and think creatively.  He also argues that while Neanderthals certainly had language, the short and retracted face of Homo sapiens would be better able to communicate clearly and rapidly.  However, Lieberman explains that the adaptation of clearer speech comes with a disadvantage.  To gain this advantage, the larnyx in humans is dropped a couple centimeters, which allows for clearer speech, but also creates the risk of choking.  It is unknown if the extinction of other species is a result of a lower birth rate or competition with Homo sapiens, but clearly, Homo sapiens had an evolutionary advantage.  Lieberman argues that this advantage could have been cultural evolution, meaning the advancement of technology and clothing.  If this technology could have helped them survive in harsh conditions, it would keep the population alive long enough to select for beneficial adaptations.  Finally, Lieberman argues that humans are adapted to be adaptable.  We have the capabilities to communicate, cooperate, invent, and think, and this allows humans to adapt to different environments.  Lieberman concludes that it is our cultural achievements such as farming and writing that have allowed humans to thrive.

Energy in the Ice Age

In this chapter, Lieberman explains how the patterns of rapid climate change affected the evolution of Homo erectus.  During the time when Homo erectus was migrating out of Africa, the Earth was undergoing cycles of ice age to rapid heating, with each cycle lasting 100,000 years.  This greatly affected Europe, which had cycles of glaciers forming and melting.  Even in Africa, which was not affected by glaciers, had wet and dry periods.  Despite the challenging time, Homo erectus not only survived, but thrived.  During the time that Homo erectus existed, brain size nearly doubled.   Around 500,000 years ago, Homo erectus learned to make spear points, and learned to use fire regularly 400,000 years ago.  Lieberman calls the discovery of fire a transformative advance.  Cooked food allows absorption of more nutrients and kills pathogens.  Fire also allowed Homo erectus to keep warm and fend off predators.  However, Lieberman focused on Homo erectus’ increased brain size, which doubled over the Ice Age.  With most other primates, as body size increases, brain size gets comparatively smaller.  However, Homo erectus does not fit this trend at all and is within the size range for modern human brain size.  But Lieberman emphasizes that larger brains come with sizable costs.  Despite being only 2% of modern humans’ weight, the brain uses up 20-25% of the energy budget, or 280-420 calories a day.  These cost are only amplified for mothers caring for children.  Additionally, large brains require extra protection from concussions and make childbirth extremely difficult.  One additional adaption necessary for large brains is the ability to store large quantities of fat.  The brain must receive a constant supply of sugar from the blood, and even short interruptions can have devastating effects.  Fat is the most efficient way of storing energy, and Homo erectus evolved to be able to store large amounts of fat efficiently.  Lieberman believes that one of the main advantages of large brains is the increased ability to cooperate with each other.  Additionally, large brains are helpful to remember and predict the location of food, or to track animals while hunting.  

The First Hunter-Gatherers

In this chapter, Lieberman argues that during the gradual cooling of the climate, natural selection favored hunting and gathering.  Lieberman argues that the first hunter-gatherers were from the genus Homo, either Homo habilis or Homo erectus.  The advantage of hunting and gathering is that plants are abundant, easy to find, and won’t run away.  The disadvantages are that plants often contain indigestible fiber and have a low nutrient density.  The plant based diet could have been supplemented with meat to increase the amount of calories consumed.  Stone tools have been discovered, indicating that meat was an important part of the diet.  Additionally, these tools could have been used to process food, because it’s difficult to chew tough plants and meat.  Lieberman also explains that hunting and gathering resulted in a division of labor and food sharing.  In fact, Lieberman argues that food sharing extended past immediate family to the whole community.   

Compared to Australopithecus, Homo erectus had much longer legs, and Lieberman argues that this is because longer steps are more efficient.  This is evidence for the Homo erectus hunter-gatherer lifestyle, because hunter-gatherers must walk long distances to find food.  Lieberman argues that the evolution of a large external nose in Homo erectus helped conserve water when Homo erectus was walking during the middle of the day.  Lieberman argues that Homo erectus was skilled at endurance running, and used the strategy of persistence hunting.  The basic premise of persistence hunting is that humans are able to cool down by sweating, but prey animals are only able to cool down by sweating.  Persistence hunting works if the hunters run constantly after an animal, giving it no time to cool down.  Eventually the animal will collapse from heat exhaustion, and won’t be able to run away anymore.  It’s unknown when sweat glands first evolved, but Lieberman believes that it evolved in the genus Homo or was expanded on after it emerged in Australopiths.  Lieberman believes that the increase in calories from adding meat (and the additional calories) to the diet made it possible for larger brains to evolve.