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.