The Story of the Human Body

Cultural buffering is an evolutionary concept in which human culture impacts biological evolution. One prominent example is that humans have few adaptations that allow them to endure cold temperatures because they wear clothes. The cultural practice of wearing clothes prevents humans from evolving physical cold-survival strategies.

Lieberman refers to the cultural practices that fail to address the underlying causes of mismatch diseases as dysevolution, or harmful evolution. For example, dental cavities are prevalent because modern humans eat high-sugar and high-starch diets. Rather than making dietary changes, humans prevent cavities through dental hygiene and through dental fillings. These treatment options allow humans to continue or increase their intake of sugary foods, thus creating a feedback loop which perpetuates cavities.

Fallback foods are foods that are less desirable. Such foods are often tougher and less palatable or nutritious. Fallback foods are critical when finding food is challenging, and, during such times, natural selection favors traits that allow individuals to consume fallback foods more efficiently. Lieberman writes, “An important point about fallback foods is that they can be the difference between life and death, so natural selection tends to act strongly on adaptations that help animals eat them” (54). An example of this is found in australopiths, who evolved to have larger teeth and chewing muscles so they could consume fallback foods when the African climate became colder and drier.

Glucose and fructose are two basic sugars found in foods high in carbohydrates. Glucose is a main component of starches, like flour, and is not very sweet, and fructose is sweet and naturally occurs in fruits, vegetables, and honey. Glucose is managed by insulin, which is produced by the pancreas, and fructose is mitigated by the liver. While the brain runs off glucose, excess glucose is stored as fat. Excess fructose is transformed into triglycerides, or fat, and is stored in the liver or released into the blood stream. Fiber slows the rate of glucose and fructose digestion, which is why foods high in both fiber and sugar, like apples, are not associated with weight gain.

Hyperbolic discounting is an economic term that refers to the prioritization of short-term costs and benefits over long-term costs and benefits. Lieberman argues that hyperbolic discounting explains why many individuals, organizations, and institutions are willing to partake in potentially harmful activities. For instance, the government is willing to sanction the use of toxic preservatives, like sodium nitrite, which prevent bacterial growth in the short-term but are carcinogenic.

The Industrial Revolution began in the late 1700s with the increase in industrialization and the rise of urbanization and factories. Lieberman defines it as “an economic and technological revolution in which humans started to use fossil fuels to generate power for machines to manufacture and transport things in massive quantities” (211).

The mismatch hypothesis is a foundational concept in evolutionary medicine which holds that health issues are caused by maladaptive traits. Adaptations are dependent on context, and modern lifestyles are vastly different from the lifestyles humans lived as they were evolving. This conflict between environment and evolved traits is called evolutionary mismatch, and the resulting health conditions are referred to as mismatch diseases. Lieberman uses the example of transplanting a zebra from the savannah to New England: While the zebra would have fewer predators to contend with, they would struggle with mismatch issues, such as struggling to find food or to stay warm.

Natural selection is an evolutionary process that relies on three cohesive phenomena—variation, genetic heritability, and differential reproductive success. Variation refers to the genetic differences between individual members of a species; genetic heritability is the idea that genes are passed from parent to offspring; and differential reproductive success refers to the variations in individual reproductive success. Traits inherited through genetic heritability, which result in genetic variation, impact an individual’s reproductive success.

Natural selection can be positive or negative. Negative selection prevents individuals from passing on unhelpful or damaging traits, while positive selection is the passing on of beneficial traits. These beneficial traits are referred to as adaptation.