Human Variation And The Concept Of Race
The concept of race is not scientifically accurate, as it is a social construct with no “biologically sound pattern” on variation. There is no end or beginning to a race because human variation is continuous. The many possibilities of skin color, seen to indicate this notion of “race”, is determined by “different proportions of the same set of alleles”.
Many think they are completely different alleles, hence these many classifications in “race”. Race is only the phenotypic presentation of human variation and their ability to adapt to the different environments. Similar skin colors evolve “independently in human populations inhabiting similar environments”. This is “known biological trait independence” because traits like this are inherited and due to the pressures in the environment that they may experience, may cluster together. Skin color shows clinal variation, as there is no direct correlation for the possibilities and the shades “grade into one another without sharp breaks”. Natural selection occurs, for those who live closer to the equator. They tend to have darker skin and more melanin to protect their skin from sunburn by “absorbing and scattering UVR and protecting DNA from damage that can lead to cancer”. Three interconnected drivers of skin color include: genes of major effect, additional polygenes of intermediate or minor effect, and input from the environment. The three drivers work together to create the phenotype we see as skin color. Pleiotropy and polygeny play a huge role in phenotypic traits. Pleiotropy is a phenotypic feature that is produced a by a single cell, while polygeny occurs when many genes combine. A gene of major effect is a gene at “one locus whose expression has a critical effect on phenotypes”. When this gene becomes pleiotropic with harmful consequences to the body, the additional polygenes of intermediate or minor effect, modifies the trait and eliminates the harm that has been created. After that, phenotypic traits are finely tuned by inputs of the environment with factors like: nutrients, temperature, humidity, altitude, or day length. It will adapt to the needs of its environment to prolong the population. This is a very complex process/ interaction.
A meaningful indication of human variation among contemporary human populations is the ability for disease resistance. Disease resistance is caused by selective pressures that are found in specific regions where a particular agent that causes these infections are known to be endemic. This causes a balanced polymorphism and entails “heterozygosity for inherited illnesses”. Amongst individuals in Africa, the Middle East, India, and Greece for example, they have developed sickle cell. In this case, they have adapted to malaria due to the high population of mosquito’s present. The sickling shape of hemoglobin cells in the individuals’ blood allows their bodies to fight off the effects of malaria and the parasite to protect their bloodstream.
Another example is Tay-sachs and their adaptation to tuberculosis. In this case, having this allele produced an enzyme that helped individuals survive the disease. Lastly, cystic fibrosis, an adaptation to cholera, has prevented individuals from losing salt as a result of diarrhea and in their mucous secretions. This shows how variations in the human population is important, as it allows higher survival rates in populations with such endemics. In class, it was discussed how this concept is the differential reproduction and survival traits that occur due to changes in the phenotype. When phenotypes are advantageous, they are passed along to future generations to prolong their populations.
