Answer
Virchow called Ernst Haeckel a "fool" because Haeckel believed in evolution and Virchow did not. Haeckel was a German biologist who is considered to be one of the founders of evolutionary biology. He was a strong supporter of Charles Darwin's theory of evolution by natural selection, and he believed that all living things are descended from a common ancestor. Virchow, on the other hand, was a staunch opponent of evolution.