Karl Popper:

In 2004, philosopher and psychologist Michel ter Hark (Groningen, The Netherlands) published a book, called Popper, Otto Selz and the rise of evolutionary epistemology, in which he claimed that Popper took some of his ideas from his tutor, the German psychologist Otto Selz. Selz never published his ideas, partly because of the rise of Nazism, which forced him to quit his work in 1933, and the prohibition of referring to Selz' work. Popper, the historian of ideas and his scholarship, is criticised in some academic quarters for his rejection of Plato, Hegel and Marx.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". When did Selz start his work?
unanswerable