Natural Selection in Modern Populations: Adaptation on Prevailing Conditions

Examples of Natural Selection in Modern Populations
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Examples of Natural Selection in Modern Populations
Introduction
In his definitive book, “On the Origin of Species” published in 1859 and later became the international bestseller, Charles Darwin, an English naturalist outlined the concept of natural selection recording his study observations during a voyage in the Pacific Islands and South America. Natural selection refers to a process that makes species become adapted to their surroundings or environment. This process is also known as the engine that powers the evolution of all species on the planet Earth. While some people might be opposed to the theory of evolution, natural selection that drives evolution supports the theory because there are countless examples of this process in everyday life. For instance, the fact that a select population develops lactose intolerance and is unable to digest lactose, also known as milk sugar, is an example of natural selection. The ability of some people to digest lactose past infancy dates back to 10,000 years ago following the agricultural revolution and dairy farming (Silanikove et al., 2015). As humans, Homo sapiens, transitioned from being hunters and gatherers to become farmers, a select population that comprised of dairy farmers became adapted to digest lactose that served as a source of energy. Therefore, it is likely that individuals that do not develop lactose intolerance today are great descendants of dairy farmers. In another observation, H. sapiens readily find mates and reproduce many children when they are slightly taller compared to the average but excessively tall and short men are disadvantaged during mate selection and having children (Stulp et al., 2015). Stulp et al (2015) have also observed that taller Dutch women experience higher child survival and this trait contributes to increased population success. Besides environmental conditions, natural selection can account for the success of different species observed in the modern context. This paper explores the topic of natural selection and explains how the process powers evolution of species, a concept first proposed by Charles Darwin, by describing that lactose intolerance, antibiotic resistance, leukemia adaptation, melanin in tropical populations, HIV susceptibility, and menstruation among women, as seen in modern populations, are events that have resulted from natural selection to make individuals better adapted to life.
Lactose Intolerance and Persistence
Dairy farming is one of the booming agricultural sectors not only in the United States but also globally, providing humans with proteins, calcium, and other nutrients derived from milk and milk products such as ghee, yogurt, cream, dried milk, condensed milk, and other derivatives. However, not every individual can digest the milk sugar, lactose due to lack of a genetic trait known as lactase persistence (LP) where the activity of intestinal lactase persists beyond childhood into adulthood. This trait of lactase persistence has been seen to vary in frequencies among different human populations and is most common among the Africans, northern Europeans, and Arabian nomadic tribes with a history of consuming fresh milk. Liebert et al (2017) have shown that the LP trait is linked to at least five independent single nucleotide variants of the lactase gene that make it possible for adults to digest lactose without developing symptoms of lactose intolerance such as flatulence and diarrhea (Misselwitz et al., 2019). Scientists have suggested that the habits of human ancestors could be the determinant of whether individuals can develop such symptoms or not after taking dairy products. In this manner, researchers argue that before dairy products were readily available, people did not require to digest milk following the weaning stage. However, about 10,000 years ago, people found it necessary to consume milk after the agricultural revolution where animals were domesticated to provide food and other necessities (Silanikove et al., 2015). This meant that humans have to develop a selective mechanism for lactase persistence and produce elevated levels of intestinal lactase, an enzyme responsible for digesting milk sugar, throughout the adult stage. One important event in human evolution included the movement of human ancestors from their roots in Africa to occupy the world. According to scientists, the migration of humans happened before they domesticated animals and obtain milk from them. Studying Africans and non-Africans, scientists have shown that Africans have high levels of lactase enzyme compared to non-Africans. Therefore, lactose intolerance and persistence are examples of natural selection mechanisms that are commonly observed in modern populations.
Antibiotic Resistance
Antibiotic resistance refers to the ability of pathogens or disease-causing microorganisms to overcome the effects of agents used to kill them or arrest their reproduction, commonly known as antibiotics. This ability evolves through a natural process selection and happens via random mutation although it can be engineered through the application of evolutionary stress on a given population. As the gene is formed, it transfers its genetic blueprint horizontally through plasmid exchanges. Bacteria that carry multiple genes that are resistant to antibiotics are known as multidrug-resistant bacteria, also known as superbugs. Scientists identify that such resistance to antibiotics is an example of evolution driven by natural selection (Harkins et al., 2017). Since the effects of antibiotics are an environmental pressure to the bacteria, the bacteria that have a certain mutation that allows them to survive to continue to reproduce and thus are said to be positively selected. These populations of bacteria are then able to pass antibiotic resistance traits to their offspring and form a fully resistant generation. Many studies have indicated that specific patterns of the use of antibiotics significantly affect the number of resistant bacteria that develop. For instance, overuse of some antibiotics such as broad-spectrum antibiotics such as cephalosporins could greatly facilitate the development of a certain type of resistance known as methicillin resistance. Besides, other practices such as the use of unnecessary prescriptions, misdiagnosis, and the use of antibiotics in animal farming could encourage the development of antibiotic resistance. One of the common examples of antibiotic resistance is methicillin-resistant Staphylococcus aureus or MRSA. This type of antibiotic resistance was first reported in 1960 but has become a common problem in many countries in the world (Harkins et al., 2017). Today, the spread of antibiotic resistance has become a major public health concern and the blame lies on the widespread use of antibiotic drugs that generates selective pressures that lead to the emergence of resistant bacterial strains. Through natural selection, bacterial pathogens have evolved such a mechanism that protects them from the harmful effects of the drugs.
Sickle Cell Anemia Trait and Malaria
The gene for sickle cell anemia is historically known to be one of the oldest forms of natural selection that took part in shaping the survival of humans living in the tropics. As people moved around in ancient times, studies show that they came into contact with pathogens, and thus natural selection took part to alter the body make-up resulting in better adaptation to new pathogens. Some of these diseases that have proved to be natural selection are malaria and leukemia. This means that when people are infected with malaria and leukemia, only those who are better adapted will survive while others will die. Malaria is a deadly disease that is prevalent in tropical zones. There are cases of malaria resistance that studies have associated with the positive natural selection for hemoglobin (Hb) S and HbC in humans despite negative health effects (Ha et al., 2019). Several inquiries have been made in the attempt to understand the reason behind Malaria infection and some of these reviews have shown that evidence largely supports the involvement of natural selection in the evolution of HbE and a protective role of HbE against malaria (Ha et al., 2019). This is why some people die of malaria while others do not. Similarly, when it comes to leukemia commonly kn...