Check’s article “How Africa Learned to Love the Cow” explores the studies and research of Sarah Tishkoff on genetic mutation and evolution of, more specifically, the gene that codes for lactase and lactase persistence within individuals in Africa. The frequency with which these genes occur fluctuates dramatically, which is noted in Tishkoff’s study on African populations, and account for tolerance and intolerance of lactose within humans (Check). It is interesting to see that environment may affect genetic mutation within individuals as well. Tishkoff’s research on lactose tolerance within humans in Africa is a revolutionary prospect, which allows others to study the issue of lactose intolerance in adult humans and view evolutionary trends in varied populations of humans, bringing new information and proof of evolution to the table.
Only certain individuals from certain populations can tolerate milk as adults due to various factors, such as the presence of the gene that codes for the production of the enzyme lactase, natural selection, and vertical gene transfer. Lactase is essential for breaking down lactose, a sugar within cow milk that would otherwise pass through a human’s digestive system undigested (Check 1). Within adult humans, the gene that codes for the production of the enzyme lactase is sometimes inactive or missing, which causes the intolerance of milk and causes lactose to have “unpleasant results” (Check 1) if ingested by an individual. On the other hand, if this gene is present, there are multiple reasons as to why these individuals have it. According to anthropological studies in the 1960s, humans who tended and reared cattle for a living generally had tolerance for milk as adults (Check 1).
This could be due to the workings of natural selection and vertical gene transfer. It is possible that the ancestors of these humans, who could tolerate milk and could take advantage of its nutritional benefits, had a higher survival rate than the individuals who could not tolerate milk; since diarrhea, which is a common result of lactose indigestion, “exacerbates dehydration” and can prove fatal during a famine or drought (Check 3).
This would then lead to vertical gene transfer, which refers to the transfer of genes to offspring from sexual reproduction. If an individual with favorable genes were to mate, his genetic code could possibly be transferred to his offspring, which explains lactase persistence within humans at present. It is interesting to note that the existence of this “lactase gene” that has such specific, easily identifiable purposes, and frequency of appearance in unrelated individuals are strong indicators of convergent evolution (Check 1).
The Homo Neanderthalensis is an extinct species that mainly survived on the hunter/gatherer lifestyle, scavenging for sustenance and hunting animals for food; with this in mind, it is highly possible that these individuals were lactose intolerant. Since the Homo Neanderthalensis were hunter/gatherers who relied on other methods of surviving than rearing and domesticating cattle, the idea of drinking milk from cattle rather than immediately killing it for meat was most likely foreign and is telling evidence that they most likely were lactose intolerant. This can be inferred due to the research presented earlier; that adult individuals with more exposure to cattle rearing were generally had a higher chance of lactase persistence than those who did not raise or domesticate cattle for survival.
Judging by past research and Tishkoff’s study in Africa, if a population was to stop drinking milk for a prolonged period of time through multiple generations due to the introduction and increased availability of other foods and resources, that population may develop a lactose intolerance that was not present before. This is due to the idea that extended experience with milk results in a higher frequency of the gene that codes for lactase production. This effect is magnified with the presence of other evolutionary and genetic trends that occur naturally such as vertical genetic transfer.
Today, lactose intolerance within adults remains a widespread issue. With the advent of lactose-free milks such as soymilk, the problem may have been somewhat appeased for lactose intolerant milk lovers. However, the fact remains that many adults still cannot tolerate milk. With the research of numerous anthropologists, geneticists, and Tishkoff, we can make sense of why this is still an issue and present educated inferences about our history.
Courtney from Study Moose
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