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Kellei J. Johnstone

Thesis: The Possible Selection of the Sickle Cell Trait in Early Homo

The selection of the sickle cell trait occurred prior to the origin of agriculture, and possibly prior to the origin of Homo sapiens. Malarial parasites evolved eight to ten million years ago, making it possible for humans to be infected with malaria as early as the time of the split between human and chimpanzee. A single point mutation in DNA transcription led to the circulation of hemoglobin S (HbS)in the gene pool, giving rise to a number of individuals homozygous for the trait. Individuals homozygous for the sickle cell trait (HbSS) exhibit signs of the disease in the skeleton. Traits of sickle cell disease mimic other forms of anemia, making differential diagnosis a primary goal in determining whether or not sickle cell disease is present in the fossil record. A diagnosis of sickle cell disease in the fossil record confirms the hypothesis that the sickle cell trait evolved prior to the origin of agriculture.