Out of Africa into a genetic bottleneck: how evolution has shaped modern disease

Two hundred million years ago, humans shared a common ancestor with worms; Homo sapiens have come a long way since then. Steady changes in the environment, due to migration patterns and climatic changes, have caused humans to become increasingly genetically distinct. These changes have affected a range of physiological aspects, from differential metabolisms tailored to available sustenance, to population-specific immune responses to dissimilar threats. Fragments of ancestral DNA live on in the present human genome, with chance encounters between anatomically modern humans and ancestral populations having resulted in the introgression of ancestral DNA fragments. This is, in part, responsible for the current expression, downregulation, or complete loss of certain alleles and phenotypic traits, and has significant health implications. These ancestral genes have impacted modern medicine, disease, and human nature immensely.