Jakob Johann Freiherr von Uexküll (; – 25 July 1944) was a Baltic German biologist who worked in the fields of muscular physiology and animal behaviour studies and was an influence on the cybernetics of life. However, his most notable contribution is the notion of Umwelt, used by semiotician Thomas Sebeok and philosopher Martin Heidegger. His works established biosemiotics as a field of research. Early life The son of Baron Alexander von Uexküll and Sophie von Hahn, Jakob von Uexküll was born in the Keblas estate, Sankt Michaelis, Governorate of Estonia. His aristocratic family lost most of their fortune by expropriation during the Russian Revolution. Needing to support himself, Uexküll took a job as professor at the University of Hamburg where he founded the Institut für Umweltforschung. Umwelt Uexküll was particularly interested in how living beings perceive their environment(s). He argued that organisms experience life in terms of species-specific, spatio-temporal, "self-in-world" subjective reference frames that he called Umwelt (translated as surrounding-world, phenomenal world, self-world, environment - lit. German environment). These Umwelten (plural of Umwelt) are distinctive from what Uexküll termed the "Umgebung" which would be the living being's surroundings as seen from the likewise peculiar perspective or Umwelt of the human observer. Umwelt may thus be defined as the perceptual world in which an organism exists and acts as a subject. By studying how the senses of various organisms like ticks, sea urchins, amoebae, jellyfish and sea worms work, he was able to build theories of how they experience the world. Because all organisms perceive and react to sensory data as signs, Uexküll argued that they were to be considered as living subjects. This argument was the basis for his biological theory in which the characteristics of biological existence ("life") could not simply be described as a sum of its non-organic parts, but had to be described as subject and a part of a sign system. The biosemiotic turn in Jakob von Uexküll's analysis occurs in his discussion of the animal's relationship with its environment. The Umwelt is for him an environment-world which is (according to Giorgio Agamben), "constituted by a more or less broad series of elements [called] "carriers of significance" or "marks" which are the only things that interest the animal". Agamben goes on to paraphrase one example from Uexküll's discussion of a tick, saying, "...this eyeless animal finds the way to her watchpoint [at the top of