Ernst Mayr was a renowned taxonomist, ornithologist, tropical explorer, historian of science, and philosopher of biology. He was also one of the leading evolutionary biologists of the 20th century. His work contributed immensely to the progression of the biological species concept. Ernst Mayr is also credited with originating the modern philosophy of biology, especially the part concerning evolutionary biology.
Renowned ornithologist Elliott Coues, known for his pathbreaking written works such as Key to North American Birds, had established the American Ornithological Union. He had also previously worked as an army surgeon and later taught anatomy. He was also briefly part of the Theosophical Society, though he later lost interest.