3
Darwin made use of a worldwide network of scientists and non-scientists to gather information. In 1867, he began to send out handwritten questionnaires about human expression, in particular to those who were in contact with non-European peoples.
Mueller was a German-born explorer and botanist who had emigrated to Australia in 1847. The letter shown here is from Darwin enclosing a copy of his questionnaire and asking for observations of aborigines living in the interior of Australia.