Asbestos was once considered a miracle substance—a wonder of the modern age, due to its role in stopping the fires that once plagued every major city. Unfortunately, it also shreds people’s lungs. Most countries were willing to live with that trade-off, until a crusading doctor named Irving Selikoff made it his life's mission to get asbestos banned.

Rickets was once a devastating disease: up to 90 percent of the children showed symptoms in some cities, including bent spines and bowed legs, and it resulted in many women dying during childbirth. The search for the cause of rickets took decades, and ended with a startling discovery—that much like plants, human beings had the ability to photosynthesize.

Leonard Darwin had a lot to live up to. He was the son of the legendary Charles, and several siblings proved to be brilliant scientists as well. But Leonard never quite measured up as a mediocre military officer and two-bit politician. In his fifties, he pronounced his life a “failure.” But in his sixties, he finally found his calling—the dark pseudoscience of eugenics, a field he embraced in part to prove that he wasn’t the failure he imagined.

A young woman in the mid-1900s couldn’t take an at-home pregnancy test. Instead, she sent a vial of urine to a clinic, where a technician would, of all things, inject it into a frog, and hormones in the urine would cause the frog to lay eggs. This frog-based test was far faster, easier, and cleaner than any pregnancy test before, and it shifted power for family planning from doctors to women themselves.

After scientists had a handle on how many chromosomes humans have, other researchers began exploring whether certain ailments might be caused by chromosomal abnormalities. To this end, a French cardiologist discovered that Down syndrome was caused by the presence of an extra chromosome in humans. But a colleague stole credit for her work, and the battle over their legacies continues to this day, in part because the colleague is on track to become a certified Catholic saint.

It seems like a simple question: how many chromosomes do human beings have? But getting an accurate count proved surprisingly hard for much of last century. In fact, virtually every textbook once cited an incorrect number, until in 1956, a fiery Indonesian scientist finally determined the true count—and had to battle his boss over who would receive credit for this legacy-making discovery.

The 1910 return of Halley’s comet was greeted with rapture around the world—at least at first. Due to irresponsible speculation by scientists about the theoretical dangers of a close encounter with a comet, many people grew terrified of Halley’s approach and took drastic measures. They fled their homes, hid out in wells or caves, even committed suicide. It’s a grave reminder of scientific communication gone very wrong.

It’s the 80th anniversary of the Dutch Hongerwinter during World War II, which led to widespread starvation, and an inadvertent breakthrough in treating deadly celiac disease.