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. Another problem is that it is difficult to tell if a disease is a result of a mismatch if possible environmental causes are unknown.
For example, brushing your teeth is a modern idea, but it is unquestionably helpful. Additionally, Lieberman makes the point that just because something is different, doesn’t mean that it is bad. Understand mismatch diseases is complicated and difficult, especially because it is difficult to determine what exactly humans are adapted for. This is not a new problem, and Lieberman explains that mismatch likely occurred as Homo sapiens migrated out of Africa. 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. He introduces the idea of evolutionary mismatch, where genes that are advantageous in one environment are detrimental in another. 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. Additionally, it is important to understand evolution to predict how infectious diseases and antibiotic resistant bacteria will respond. 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. 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 new chronic conditions are not from new genes, but from how genes interact with a new environment. 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. 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.
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. Conversely, farming and industrialization has promoted both infectious and noninfectious diseases, as well as famines and malnutrition. 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. In this chapter, Lieberman debates the merits of living like a Paleolithic hunter-gatherer.
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