Radiobiology

Radiation responses are
evolutionary ancient

Early Earth was a high-radiation environment when life emerged over four billion years ago.^[1] Cosmic radiation was more intense before the geomagnetic field strengthened, the UV index was much higher until Earth’s ozone layer formed, and natural radioisotopes in the rocks and soil were more abundant at the surface.^[2] Because ionizing radiation was unavoidable and severe, any replicating genetic polymer (predecessors of life) would need repair systems extremely early in evolution. The leading theory is that these repair systems pre-date the DNA molecule and emerged in the so-called RNA World.^[3,4,5] Primitive RNA repair systems would have given protocells a survival advantage. Thus, ionizing radiation may have been a major driver for the emergence of repair mechanisms even before DNA existed.

When life transitioned from RNA to DNA, the high-energy radiation environment remained a constant threat to the genome. To survive and maintain fitness, organisms adapted and evolved sophisticated pathways to recognize and repair DNA damage. ^[4,6] As life became more complex, so did radiation responses. Today, we organize the field into several categories, for instance by purpose (normal tissue protection versus cancer radiotherapy), by level of complexity (cellular, tissue, or systemic effects), or by analytical approach (spatial transcriptomics, radiogenomics, free radical biochemistry, and many more.).