Environment, Ancestry, and Race Theme Analysis

Just as the evolution of other organisms has had a major effect on human evolution, the environment in which people live also plays an important role in making certain genes more advantageous. Whether it is a population’s exposure to sun, the climate in which one’s ancestors lived 10,000 years ago, or different social customs that have developed in particular areas of the world even in the past few centuries, our ancestors’ environment has been a key factor in the development of our genetics. The environment dictates different physical traits and behaviors among different groups of people, and so Moalem argues that this relationship between environment and ancestry serves as one of the building blocks to our ideas of culture and race.

In order to illustrate the idea of environment impacting human evolution, Moalem considers how the climate that early humans experienced caused them to develop certain adaptive traits. Moalem first looks at how a period of extreme cold added evolutionary pressure to those who lived in cold environments, causing them to be more likely to develop diabetes. The previous ice age, Moalem recounts, was followed by a period of warmer weather, in which human populations migrated out of Africa and into Europe, which had previously been too cold to be habitable during the ice age. Then, around 12,000 years ago, there was a rapid shift (occurring over just a decade) back to colder weather. This resulted in a period called the Younger Dryas, which lasted more than 1,000 years. During this period, it is likely that thousands of humans froze or starved to death in those colder areas. However, those who survived adapted in ways both social and biological. It is believed that diabetes may have actually allowed people to live by increasing the sugar concentration in people’s blood, which provided them with a higher chance of not freezing to death. There were additional social developments from the Younger Dryas that changed parts of our genetic code as well. For instance, many scientists believe that this colder period led to the first development of agriculture in Northern Europe and the collapse of hunter-gatherer societies in the area. Moalem posits that because of the development of dairy farming over time in these Northern European areas, populations from those areas are more likely to have enzymes that can break down lactose in milk and are therefore less likely to be lactose intolerant than people from other ancestral lines—another illustration of how geographic and social conditions can affect one’s genes.

The idea that geography and our ancestor’s environment can affect our genetics becomes tied up in the complicated idea of what race actually represents on a biological level. While Moalem shies away from trying to define what race means, he acknowledges that “distinct populations do share distinct genetic heritages, which are almost certainly the result of different evolutionary pressures our various ancestors experienced as they settled and resettled across the globe.” He argues that the prevalence of genetic mutations in certain ethnic groups is largely based on common environments and social conditions. In our ancestors, skin color was determined largely by sun exposure. Those with more exposure produced more melanin (which causes darker skin), blocked more ultraviolet light, and therefore protected their folic acid, which is integral to cell growth. Those with less sun exposure produced less melanin because ultraviolet light absorption is crucial in one’s vitamin D production. These skin color adaptations, which were developed over thousands of years, play a large role in several key health issues: for instance, people who have little access to sunlight (like Northern Europeans) have trouble maintaining healthy levels of vitamin D. People with very dark skin are also unable to absorb the necessary ultraviolet light that allows them to create vitamin D. Due to this deficiency, both groups have evolved to produce a protein called apolipoprotein E (ApoE4). This protein increases the amount of cholesterol in the bloodstream, which can then be converted to vitamin D. But this comes with a tradeoff: the extra cholesterol also puts people at greater risk for heart disease, stroke, and Alzheimer’s disease. Our ancestors’ varied environments thus had a major effect on our skin color, which in turn can affect one’s health conditions for generations, even after leaving that environment.

Moalem also delves into how cultural factors that arise from different geographic locations can change certain people’s genes in ways that are distinct from other groups. For instance, people of Asian descent frequently have a genetic variation which makes it difficult to break down alcohol, causing them to appear and often feel more drunk. People of European descent, however, rarely have this variation. This is because, as humans settled into cities and towns, the dilemma of how to clean water first arose. In Asia, people purified water by boiling it and making tea. In Europe, they used fermentation, and the resulting alcohol from that fermentation killed microbes, even when it was mixed with water. As a result, Moalem writes, “there was evolutionary pressure in Europe to have the ability to drink, break down, and detoxify alcohol, while the pressure in Asia was a lot less.” Geographic location and the cultural customs that accompany that location both clearly affect the genetic makeup of populations who live there.

Moalem sums up his point about environment and ancestry as such: “One thing is clear—there is mounting evidence that where our ancestors came from, how they adapted to manage their environment, and where we live today all combine to have a significant impact on our health.” His main project, as with exploring the other factors that help us understand our genetics, is to provide a greater understanding for why we have certain conditions and therefore to find more effective ways to treat ourselves if we move to new environments where those conditions are no longer beneficial.