The genetic makeup of human beings is complex and varies across the globe. Some genes are geared towards traits that protect the body in different environments. Changes are theorized to have happened over many years as humans have evolved and have been affected by the world around them. Some changes are easily noticed, such as the lack of wisdom teeth in some modern humans. Others, such as sickle cell anemia, go unnoticed until symptoms arise.
The sickle cell gene can be present in an individual as a carrier gene or as fully symptomatic. The difference lies in the number of genes passed down. Both parents of a child must pass down the gene for their offspring to be positive for the illness. One gene causes a person to be a carrier only. The genetic complication that causes the sickle cell trait is located sixth on the hemoglobin beta chain. Glutamate is usually housed at this location. In sickle cell individuals glutamate is replaced by valine. Full sickle cell disease leads to a shortened lifespan while carrying the trait allows for a normal life span. Natural selection would normally contribute to a lesser number of sickle cell gene carriers. The sickle cell gene, however, is known to offer some protection against malaria. This protective quality has allowed for unusual perseverance of this negative health issue.
Sickle Cell Disease
When a person tests positive for sickle cell disease it refers to the shape of their red blood cells. The cells are shaped more like a “C”, or a sickle, rather than round. The hemoglobin that carry oxygen throughout the body are affected, causing a toxic buildup of dangerous gases. This extra carbon monoxide may be a part of what halts the symptoms of malaria in sickle cell carriers.
Natural selection plays a part in the perseverance of a healthy human race. Genetic traits that cause illness are often minimal in populations. Reproduction can be halted when genetics do not line up properly. Healthy individuals, in natural situations, are more likely to reproduce. In past civilizations, those with health issues or genetic mutations may not have survived long, lessening the possibility of their disability recurring in the population. Modern medical intervention, however, has allowed for the survival of previously fatal complications. Those with sickle cell disease suffer from illness and may not live as long. They may, however, reproduce. Natural selection has taken a twist in areas where malaria is persistent.
In areas with high malaria risk, the sickle cell gene is noticeable at a high rate. This phenomenon occurs because those with the gene have a natural resilience to malaria, which can be deadly. Carriers of the sickle cell gene do not have active symptoms of sickle cell and also have protection against malaria. This ensures a higher survival rate of sickle cell carrying individuals than those without the gene. This negative gene has managed to work around natural selection. The genetic predisposition to malaria resilience is treated by the body as a positive survival trait, despite the dangers of sickle cell disease. A higher number of sickle cell carriers, instead of the general population, may survive during a large malaria outbreak. These individuals then continue to reproduce, increasing the genetic possibility of sickle cell disease.
The highest protection offered is about 60% in those with the sickle cell gene. A natural resistance to malaria is usually built up later in life for those in susceptible areas. The mortality rate of young children from malaria, however, can be fairly high. The sickle cell gene is particularly protective for babies and young children. This unusual genetic link, therefore, continues to survive.
Research is ongoing to determine whether the sickle cell and malaria link can be replicated and used to save lives. The genes offer an effective natural alternative to severe malaria symptoms. The protective qualities of the sickle cell gene have caused a continuation of the disease in certain populations, while lowering mortality rates of malaria. The perseverance of the gene, however, puts these populations at risk of increased sickle cell disease. The link may help scientists solve some mysteries of how certain genetic traits survive and others do not.