De Vries was born on February 16, 1848. He grew up in Haarlem, an area in the Netherlands rich with plant life. During vacations from school, he would roam the countryside picking up more plants for his growing collection. By the time de Vries entered the University of Leiden in 1866, he was already an expert on plants of the Netherlands and turned to other related areas of study. One of those areas was evolutionary theory--an interest brought on by Charles Darwin's book The Origin of Species. De Vries thought a major flaw in Darwin's work was that Darwin could not identify what caused evolution, the changes in organisms. De Vries set out to develop his own theory.

In 1886, while de Vries was out for a walk, he came upon a field of flowering plants called evening primrose. He noticed that some of the specimens differed widely. He took samples back...