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.