Hans Spemann (1869 – 1941) was a German zoologist whose experiments established the importance of interactions among tissues during embryonic development. He studied medicine and natural science at Heidelberg, Munich, and Würzburg, and earned his doctorate under Theodor Boveri in 1895. After appointments at Rostock and the Kaiser Wilhelm Institute for Biology in Berlin, he became professor of zoology at Freiburg in 1919. His laboratory became a major center of experimental embryology

    Spemann developed delicate micro-surgical techniques to investigate how embryos establish their body plans. His early experiments used a fine hair from his infant daughter's head to constrict salamander eggs across several planes, and demonstrated that the divided embryonic material could produce twins under appropriate conditions. By transplanting early tissue from the embryonic eyes, he showed that eyes could be induced in other areas of the epidermis  In the early 1920s, his doctoral student Hilde Mangold transferred the dorsal lip of the blastopore between newt embryos whose pigmentation differed. The transplant induced a secondary body axis, and the pigmentation differences revealed that host cells contributed substantially to its tissues. In 1924, Spemann and Mangold published their results jointly in 1924. Mangold  died in an accident later that year: Spemann received the 1935 Nobel Prize in Physiology or Medicine for the organizer effect. The modern name Spemann–Mangold organizer recognizes her essential contribution.

    In 1938, Spemann published Embryonic Development and Induction, which summarized his experiments and interpretations. He also proposed nuclear transplantation as a test of whether a nucleus from a specialized cell could direct the development of an entire organism. That proposal anticipated later experiments in nuclear transfer and cloning.