Ernst Haeckel was born in Potsdam, Germany. As a young boy he was interested in nature, particularly botany, and kept a private herbarium, where he noticed that plants varied more than the conventional teachings of his day advocated. Despite these natural interests, he studied medicine—at his
father's insistence—at Würzburg, Vienna, and Berlin between 1852 and 1858. After receiving his license he practiced medicine for a few years, but his desire to study pure science won over, and he enrolled at the University of Jena to study zoology. Following completion of his dissertation, he served as professor of zoology at the university from 1862 to 1909. The remainder of his adult life was devoted to science.

Haeckel was considered a liberal non-conformist of his day. He...