Uncertainties associated with low-dose exposures to chemicals that are known to be hazardous at high doses were probably being raised at the dawn of human civilization when Homo sapiens began distinguishing among edible, near edible, and poisonous plants. The study of toxicology began around the sixteenth century with the writings of an Austrian physician and contemporary of Leonardo da Vinci, named Philip von Hohenheim, who practiced “chemical medicine.” Hohenheim is more popularly known as Paracelsus, a name he adopted to elevate him above a prominent Roman physician named Celsus. Paracelsus is known to have said: “All things are poison and