Final answer:
Sir Francis Galton, a cousin of Charles Darwin, is credited with inventing the self-report questionnaire, which is a significant tool in social sciences for collecting opinions and data on various matters.
Step-by-step explanation:
The notable individual who was a cousin of evolutionary theorist Charles Darwin and is credited with inventing the self-report questionnaire is Sir Francis Galton. Galton was an English polymath who made significant contributions to various fields, including statistics, psychology, and biology. He was interested in measuring human intelligence and was a pioneer in the field of psychometrics, the science of measuring mental faculties. His development of the self-report questionnaire represented an early attempt to systematically gather data about individual opinions and attributes on various matters, influencing future psychological assessments and surveys.
Galton's work in this area was part of his broader interest in heredity and human abilities, which was somewhat inspired by Darwin's work on evolution. Nonetheless, Galton's methods of data collection through questionnaires remain an integral part of social sciences research and have evolved to become more sophisticated and reliable.