Diet is a big force behind recent human evolution because 10,000 years ago humans transitioned from being hunter-gatherers to farmers and their bodies had to adapt to new foods. The best-known example involves the gene that regulates a person's ability to make an enzyme required to digest lactose, the sugar in milk. Historically, the LCT gene shut down in childhood as babies were weaned off breast milk. But after cows, sheep and goats were domesticated, people with a mutation that allowed them to drink milk in adulthood had a nutritional advantage that made it easier for them to propagate their genes. DNA analyses have shown that the mutation cropped up in Europe about 8,000 years ago, quickly spreading all the way to India. Today, it is carried by more than 95 percent of people of northern European descent. A 2007 study bolsters the theory that the rise of pastoralism prompted the gene's spread. Using new techniques to analyze ancient DNA, German and British researchers checked the genes of eight European farmers who lived 7,000 to 7,800 years ago, before the widespread adoption of a herding lifestyle. None of the early farmers had the mutation for lactose tolerance.
While many of us may carry the mutation to better tolerate lactose, it has not adequately exerted its effect in limiting the symptoms associated with lactose intolerance as of yet. Three-quarters of the human population are still considered lactose-intolerant and many exhibit debilitating symptoms.
Even more apparent is how the human genome is still adapting to our relatively new agricultural diet based on starches and sugars. Type 2 diabetes and other chronic inflammatory diseases are some of the consequences. Scientists have compared the genetic profiles of diabetes patients to those of healthy controls and found some recently spreading genes that seem to protect against diabetes by affecting the body's ability to digest starches. That may explain why Native Americans, who came to farming relatively recently, have a higher risk of diabetes, Hawks said. However, those protective genes are active in a select few.
Celiac disease and gluten intolerance, the inability to process the glue in grains, is a perfect example of how the human genome has not yet evolved. At least one in 133 Americans are diagnosed with celiac disease and the ratio keeps getting smaller. If we are in the midst of an evolutionary transition, if history is an indication, it will take a lot longer for us to be able to tolerate sugars and starches.
Here are the two research studies related to this issue that we cite the most:
"Whereas major changes have taken place in our diet over the last 10,000 years since the beginning of the agricultural revolution, our genes have not changed. The spontaneous mutation rate for nuclear DNA is estimated at 0.5% per million years. Therefore, over the past 10,000 years there has been time for very little change in our genes, perhaps 0.0005%. In fact, our genes today are very similar to the genes of our ancestors during the Paleolithic period 40,000 years ago, at which time our genetic profile was established. Genetically speaking, humans today live in a nutritional environment that differs from that for which our genetic constitution was selected. Studies on the evolutionary aspects of diet indicate that major changes have taken place in the type and amount of essential fatty acids and in the antioxidant content of foods." Simopoulos, Artemis, MD, Nutrition Reviews, Vol. 57, No. 5, May 1999
"There is growing awareness that the profound changes in the environment (eg, in diet and other lifestyle conditions) that began with the introduction of agriculture and animal husbandry 10000 y ago occurred too recently on an evolutionary time scale for the human genome to adjust. In conjunction with this discordance between our ancient, genetically determined biology and the nutritional, cultural, and activity patterns of contemporary Western populations, many of the so-called diseases of civilization have emerged. In particular, food staples and food-processing procedures introduced during the Neolithic and Industrial Periods have fundamentally altered 7 crucial nutritional characteristics of ancestral hominin diets: 1) glycemic load, 2) fatty acid composition, 3) macronutrient composition, 4) micronutrient density, 5) acid-base balance, 6) sodium-potassium ratio, and 7) fiber content. The evolutionary collision of our ancient genome with the nutritional qualities of recently introduced foods may underlie many of the chronic diseases of Western civilization.
Evolution acting through natural selection represents an ongoing interaction between a species’ genome and its environment over the course of multiple generations. Genetic traits may be positively or negatively selected relative to their concordance or discordance with environmental selective pressures (1). When the environment remains relatively constant, stabilizing selection tends to maintain genetic traits that represent the optimal average for a population (2). When environmental conditions permanently change, evolutionary discordance arises between a species’ genome and its environment, and stabilizing selection is replaced by directional selection, moving the average population genome to a new set point (1, 2). Initially, when permanent environmental changes occur in a population, individuals bearing the previous average status quo genome experience evolutionary discordance (2, 3). In the affected genotype, this evolutionary discordance manifests itself phenotypically as disease, increased morbidity and mortality, and reduced reproductive success (1-3). Similar to all species, contemporary humans are genetically adapted to the environment of their ancestors—that is, to the environment that their ancestors survived in and that consequently conditioned their genetic makeup (1-3). There is growing awareness that the profound environmental changes (eg, in diet and other lifestyle conditions) that began with the introduction of agriculture and animal husbandry 10000 y ago occurred too recently on an evolutionary time scale for the human genome to adapt (2-5). In conjunction with this discordance between our ancient, genetically determined biology and the nutritional, cultural, and activity patterns in contemporary Western populations, many of the so-called diseases of civilization have emerged (2-12)."
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