HERMANN JOSEPH MULLER FOUND HIS CALLING IN THE FLY ROOM—a storied laboratory at Columbia University where Thomas Hunt Morgan first made the connections between genes, chromosomes and heredity. The room was filled with jars of common fruit flies, whose short life spans made them ideal for studying genetic traits. 

When Muller moved to the University of Texas in Austin in 1920, he set up his own fly room to study why deadly mutations suddenly appear in the genetic code. He thought that external influences, such as temperature, might play a role. With a wet cloth and an electric fan, he kept one set of lab cultures several degrees cooler than the others in the hot climate and found that heat alone could increase mutations. 

Then Muller looked at the effects of various forms of radiation, which led to his landmark discovery, in 1927, that exposure to high-energy radiation could induce major chromosomal changes. The stronger the radiation, the greater the damage. 

Muller’s discovery opened a new chapter in genetics, with the first proof that human influence could manipulate genes. As he put it in 1928: “Mutation … does not stand as an unreachable god playing its pranks upon us from some impregnable citadel.” 

His findings were slow to reach the general public. X-rays in particular enjoyed popularity as a medical breakthrough and novelty. Shoe stores advertised the “Foot-O-Scope” and “Pedoscope,” gadgets that used X-rays to size the feet of customers, especially children. “Now, at last, you can be certain that your children’s foot health is not being jeopardized by improperly fitting shoes!” one radio ad proclaimed. 

In 1946, Muller was awarded the Nobel Prize in Physiology or Medicine. His acceptance speech, little more than a year after the bombings at Hiroshima and Nagasaki, ended on a cautionary note about the genetic risks of atomic energy, “a potent source of permanent contamination.”

As a Nobel laureate, Muller found a more receptive audience. Scientific journals soon began publishing papers about the dangers of shoe-fitting machines, leading to better regulation and their eventual ban in the 1970s. In 1949, the United States, Canada and the United Kingdom convened a series of meetings to establish shared standards for radiation dose limits. 

Muller continued to raise the alarm about “insidious” damage from nuclear weapons that might not be visible for years. But in a world still dazzled by the dawn of the Atomic Age, his early messages met with resistance. It wasn’t until later in his life that the world caught up with Muller’s concern about the havoc technology can play on the fragile genome.