The process of DNA recombination is described: it is often harmful but occasionally may provide a benefit. The ancient invasion of ALU transposons in human genes has provided many possible loci for such chromosomal segments to align during gene repair and lead to swapping of DNA segments between chromosomes. Different types of recombination are described. Recombination of sets of segments within antibody genes leads to the enormous number of possible antibodies. Description of antibody structures, with variable regions as sites that bind to specific antigens. Occurrence of autoimmune diseases. The origin of human races is described, largely a result of changing productions of melanin pigments by tyrosinase isozymes, which originated in skin cells as a protection against UV radiation that could cause various skin cancers. The synthesis of vitamin D in skin cells is described and explains the limited concentration of melanin pigments that are necessary for health. A diet based on cereal grains provides ergosterol, a much less efficient precursor for vitamin D than the dehydrocholesterol found in meat, and may explain why lighter skin became necessary with such dietary patterns. An explanation of medical radiation terminology, with sickle cell anemia as an example of a helpful mutation. A process for the formation of sickled hemoglobin is described, as well as current medical therapies for this disease.