My understanding is that historically, schizophrenia has been presumed to have a partly genetic cause since around 1910, out of which grew an intermittent research program of family and twin studies to probe schizophrenia genetics. An opposing camp that emphasized environmental effects emerged in the wake of the Nazi eugenics program and the realization that complex psychological traits needn't follow trivial Mendelian patterns of inheritance. Both research traditions continue to the present day.

Edit to add - Franz Josef Kallman, whose bibliography in schizophrenia genetics I somewhat glibly linked to in the grandparent comment, is one of the scientists who was most firmly in the genetic camp. His work (so far as I know) dominated the study of schizophrenia's causes between the World Wars, and for some time afterwards.