Mayr, Ernst (1904-2005) was a German-born American biologist who helped develop the synthetic theory of evolution, which combines evolution theory with genetics and other sciences. Mayr also developed theories for how species evolve.

Mayr was one of three sons of Otto Mayr, a judge, and Helene Pusinelli Mayr. He was born in Kempten, Germany, on July 5, 1904. Mayr received a broad early education. He especially enjoyed bird watching, and, at age 18, he became the first in nearly 80 years to observe a pair of red-crested pochards, a species of duck. This discovery led him to meet Erwin Stresemann, Germany's leading ornithologist, or specialist in the study of birds.

Following family tradition, Mayr became a medical student at the University of Greifswald. However, at Stresemann's urging, he pursued his interest in birds and worked during summer vacations at the University of Berlin's zoological museum. By 1925, Mayr had decided to devote himself to zoology. He received his doctoral degree in zoology, with top honors, from the University of Berlin in 1926. That year, he became assistant curator to the zoological museum and remained in that post until 1932.

During those years, Mayr completed his most important early work, on the ornithology of the Pacific Ocean. In 1928, a top British zoologist invited Mayr to undertake an ornithological expedition to a remote area of western New Guinea. Mayr arrived there in April and explored the bird life of three mountain ranges. In 1928–1929, Mayr undertook a New Guinea expedition to the Saruwaged mountains and Herzog mountains. In 1929–1930, he explored the Solomon Islands as a member of the American Museum of Natural History's Whitney South Sea Expedition.

Mayr moved to the United States in 1931. In 1931–1932, he worked as a research associate in ornithology at the American Museum of Natural History in New York City. He was named associate curator of the museum's Whitney-Rothschild Collection in 1932, the same year that he became a U.S. citizen. In 1935, Mayr married Margarete Simon. They had two children.