Final answer:
The principle of informed consent dates back to the 1970s after the Tuskegee study. Informed consent became a requirement to protect human subjects in scientific research projects.
Step-by-step explanation:
The principle of informed consent dates back to the 1970s. Before that, there were few ethical guidelines for researchers to follow when studying human subjects. The infamous Tuskegee study, conducted from 1932 to 1972, where African-American men were not treated for syphilis, played a significant role in changing this. In 1974, Congress passed legislation requiring informed consent as a means to protect human subjects in scientific research projects.