Sickle Cell Anemia is a disorder in which red blood cells become hook-shaped, which causes those hook-shaped blood cells to get caught in small bloodvesselss, which then prevents oxygen and blood from getting to certain parts of the body. Since this disease is so prevalent in the African community, many people think that it is a disease that only Africans can contract and that any other population that gets SCA must have African ancestry.
I touched briefly on Sickle Cell Anemia in my post IQ, Nutrition, Disease and Parasitic Load. Mainly that SCA is correlated with decreased skull size, and therefore a decreased IQ. Though, there are some misconceptions about SCA that will be expelled today such as SCA being a marker of ancestry and the exact causes of contraction of the disease. Since most people only hear about Africans and African descended people with SCA, the misconception is that SCA is a disease that only Africans get. People then assume that any other population that gets SCA must have African ancestry, but this is not the case.
Elguero, et al (2015) took a total of 3,959 blood samples from 195 random villages dispersed throughout Gabon. They discovered that every ten-year increase in age of someone with an increase of 5.5 percent of by Sickle Cell Trait carriers. They also bring this up about evolution:
These strong associations show that malaria remains a selective factor in current human populations, despite the progress of medicine and the actions undertaken to fight this disease. Our results provide evidence that evolution is still present in humans, although this is sometimes questioned by scientific, political, or religious personalities.
Our results concern present day human populations (persons born 15–80 y ago) and clearly show that, at least in human populations of low income, such as in our study, where medical advances remain limited, biological adaptation is still an outcome driven by evolution to respond to environmental pressures imposed by pathogens, in particular malaria.
Biological adaptation is the cause for SCA developing to fight off malaria. This study proves evolution, yet, as alluded to in the quote above, Creationists still say that SCA does not prove evolution. Since selection for SCA occurs due to malaria over time, that is a clear example of evolution in action. SCA is inherited from both parents. However, if one gets the gene from one parent and not the other, they will carry the Sickle Cell Trait or SCT, and possibly pass SCA on to a future child if a partner also has the SCT.
There are many misconceptions about SCA, mainly that it is only present in black populations and those populations with some African ancestry. Since SCA evolved to fight off malaria, SCA will be prevalent in those populations that have high rates of malaria. It is mostly prevalent in areas where it is warmer and there is a lot of still water due to that being the best breeding ground for mosquitoes. The mosquitoes then transmit malaria, and those with SCA and the SCT can better fight off the malarial infection. SCA is also prevalent in Sicily and Southern Italy, Greece, Turkey and parts of India, showing that it’s not a ‘black disease’, but a disease that arises due to a higher rate of malaria due to more mosquitoes and still water being around.
- stroke – where the blood supply to part of the brain is cut off
- increased vulnerability to infection
- acute chest syndrome – where the lungs suddenly lose their ability to breathe in oxygen (often the result of an infection)
- pulmonary hypertension – where the blood pressure inside the blood vessels that connect the heart to the lungs becomes dangerously high
Since American blacks have higher rates of hypertension (among the highest rate in the world), this causes more complications when SCA arises due to already impaired blood vessels due to the higher blood pressure from hypertension, which is exacerbated by smoking. Higher rates of hypertension can then be attributed as another cause of death of those who die from SCA since their blood vessels were already put under pressure due to their hypertension.
Sickle Cell Disease (SCD) affects around 100,000 Americans, is found in 1 out of 365 black or African American births, occurs in one out of 16,300 ‘Hispanic’ births (other populations from a tropical area), and 1 in 13 blacks are born with the SCT. Since 1 in 13 blacks are born with the Sickle Cell Trait, the prevalence of blacks with SCA in America will only increase due to the SCT being more prevalent in black populations.
So far, the only known prevention of Sickle Cell Disease is not to have children. This is because it is a genetic disorder, one that evolved in populations that evolved in areas with more mosquitoes and malaria-infected mosquitoes. Though, in the future with CRISPR Cas9, it will be able to circumvent the genetic mutation that causes SCD. Researchers discovered that changes to a small patch of DNA in the enhancer region of the BCL11A gene show that it is possible to circumvent the genetic defect that causes SCA and other blood diseases such as thalassemia.
SCA, SCT, SCD and any other Sickle Cell disorder traits are not exclusive to African populations. They were selected to fight malaria and is more proof of human evolution at work. SCA evolved to fight off malaria and is prevalent in places with high amounts of mosquitoes (i.e., places with a lot of still water) as well as tropical and semi-tropical locations due to those areas being the best breeding ground for mosquitoes. Creationists deny the evolution of SCA, however, we know that they will do and say anything to prove their case that evolution does not exist.