Questions: The roots of modern personality psychology can be traced to developments in the 19th century biological sciences based on the work of R. Descartes. M. Mead. C. Darwin. T. Roosevelt. I. Newton.

The answer is C. Darwin.

René Descartes was a 17th-century philosopher and mathematician known for his contributions to philosophy and the development of Cartesian dualism, which separates the mind and body. While his ideas influenced many fields, they are not directly linked to the roots of modern personality psychology.

Margaret Mead was a 20th-century cultural anthropologist whose work focused on the social and cultural influences on human behavior. Although her work is significant in understanding personality within cultural contexts, it does not trace back to the 19th-century biological sciences.

Charles Darwin, a 19th-century naturalist, is best known for his theory of evolution by natural selection. His work laid the foundation for understanding the biological basis of behavior and individual differences, which are crucial elements in the study of personality psychology. Darwin's ideas about variation and adaptation have had a profound impact on the field.

Theodore Roosevelt was the 26th President of the United States and is not associated with the development of personality psychology or the biological sciences.

Isaac Newton was a 17th-century physicist and mathematician known for his laws of motion and universal gravitation. His work is foundational in physics but not directly related to the development of personality psychology.