sentences:  In 1955 Schmalhausen was one of the signatories of the "Letter of 300"a collective letter by three-hundred scientists denouncing Lysenkoism.He died on October 7, 1963 in Leningrad.Schmalhausen's law is a general principle that a population living at the boundary of its tolerance, in extreme or unusual conditions with regard to any aspect of its existence will be more vulnerable to small differences in any other aspect.