In order to demonstrate how modern humans became maladapted to their present day environments, which in turn increased their susceptibility to rare and previously unknown diseases when compared to their Paleolithic predecessors, one has to understand how humans evolved throughout time. By observing the earliest hominid species onwards, Lieberman analyzes the five major biological transitions in hominids relative to when they first appeared. The first transition is habitual bipedalism, and with bipedalism came various human adaptations such as hip shape, S-shaped spine, etc. Bipedalism was selected “to help the first hominins forage and obtain food more effectively in the face of major climate change that was occurring when the human and chimpanzee lineages diverged” (Lieberman 50). Bipedalism affected not only posture but dietary intake as well, and it allowed hominids to save energy while traveling farther than other quadruped or occasionally bipedal primates. Bipedalism led hominids to new food sources, which dramatically impacted dentition shape and strength. Dental adaptations reflected the importance of specific types of diets such as frugivory, omnivory, etc. Humans evolved to run, as archaic humans frequently engaged in persistence hunting which allowed them to utilize their intelligence and athleticism to become hunter-gatherers. Reliance on hunting large, fast prey resulted in an upgrade in weaponry, and their energy-filled hunter-gatherer diets led to an increase in brain size. By increasing brain size, humans prolonged their life history periods and added a stage of childhood, which is uniquely human. Archaic humans also had to gather and consume more calories in order to maintain their larger brains, slower developing bodies, and dependent offspring. Finally, archaic humans gained language, cooperation, and culture, which resulted in a new form of evolution: cultural evolution.
Two other crucial transitions that were not a product of biological evolution but rather cultural evolution included the rise of the Agricultural and Industrial Revolutions, which dramatically altered the environment and therefore the human body. Cultural adaptability allowed hunter-gatherers to thrive in various environments, but it also reduced and eventually eradicated the need for hunting and gathering altogether. Cultural evolution “has not only driven but sometimes even accelerated selection” (Lieberman 186). The agricultural revolution gave rise to evolutionary mismatches, where a particular species is maladapted in a particular environment. In this case, it describes how humans evolved specific adaptations from bipedalism, varied diet, etc., that do not work well with their constantly changing environments. Now that hunter-gatherers settled down and began domesticating plants and animals, their environments have tremendously changed as farmers began to permanently settle in a single location. These settlements promoted an increase in population density, as farmers cultivated enough food to sustain larger families than hunter-gatherers. However, these communities lacked proper sanitation; as a result, these living conditions gave birth to various diseases and plagues. Although farming generated a surplus of food, farmers would engage in trade, which allowed them to spread bacteria and microbes that provoked diseases onto other communities. Trading allowed for diseases to quickly spread and infect other communities at different and farther locations. Living in close proximity to livestock also exposed humans to infectious disease. Agricultural diets lacked variety, which resulted in numerous mismatched diseases such as nutrient deficiencies. “Relying heavily on a few crops . . . has other serious disadvantages, the biggest being the potential for periodic food shortages and famine” (Lieberman 220). Compared to hunting and gathering, farming was much more laborious and risky as farmers could potentially starve if their crops should fail to grow. With farming came potential starvation, which is something that hunter-gatherers never had to experience. Because hunter-gatherers lived in groups with low population densities, they cooperated with one another and shared their hunt to ensure that they and their families would not starve.
Although not central to this blog, the Industrial Revolution section of the text is still somewhat relevant, as this revolution could not have occurred without the establishment of agriculture. The Industrial Era was at first extremely demanding and laborious, but machines eventually ended up replacing manual human labor. Food could be cheaply processed by factories in large quantities, which created an abundance of foods high in fat, starch, sugar, and salt that were affordable to humans. Humans used to hunt and gather just enough food so they could have energy to last them until the next hunt; however, just as the agricultural revolution provided farmers with surplus of food, the Industrial Revolution produced food so cheaply that humans now have an excess of food, and their bodies did not evolve to handle this amount of energy. Food was now extremely modified and processed to evoke desirability from the masses, while the actual nutritious quality was deteriorating to low nutritional levels. Industrialization had trade offs where sanitation and producing food was improved while nutritional levels of the food plummeted. Food also became so processed and soft that it reduced the intensity of chewing. Bipedalism freed hunter-gatherers’ hands, which allowed for them to dig for food. Moreover, they would often feast on tough underground storage organs (USOs) required them to spend hours upon hours chewing since the USOs had strong, thick outer shells Once cultural evolution gave rise to the agricultural and Industrial revolutions, humans began to consume foods that are much more softer and mushier, which causes the teeth and jaw to become underused. The sugary processed foods also cause cavities, which is another problem that hunter-gatherers had never experienced before since their diets did not heavily consist of sugar. The Agricultural and Industrial Revolutions dramatically changed the way humans behaved, ate, and lived; therefore, it dramatically changed their bodies and their susceptibility to various mismatched diseases.
Overall, Lieberman emphasizes that humans are still evolving and will continue to evolve through cultural evolution. By looking into our ancestors’ past, we can observe how hominids adapted to their environments and which trade-offs occurred with the rise of the Agricultural and Industrial revolutions. By using hunter-gatherers as an example, we can apply this knowledge to prevent the various mismatched diseases that modern humans experience in the present and future. Instead of treating the symptoms of a disease for a quick fix, Lieberman presses that it is the cause of the diseases that should be addressed in order to thoroughly prevent them. Mismatched diseases occurred as humans began to evolve culturally, and various other mismatched diseases are bound to come into existence as long as humans culturally evolve. As long as mismatched diseases are around, it is best to utilize the knowledge that we have on human evolution (which includes knowledge of how the transition to agriculture affected humans) and apply it to our treatment of these diseases.
