Efforts to eliminate or neutralize the coverage of evolution in high school biology textbooks in the United States have persisted with varying degrees of intensity and success since the 1920s. In particular, the coverage of human evolution has been impacted by these efforts. Evidence of the success of these efforts can be chronicled by the emphasis given to human evolution in secondary biology textbooks historically and in the current state science standards. Prior to the 1960s, biology textbooks provided little emphasis to human evolution. In the 1970s and early 1980s textbooks reduced the coverage of human evolution. However, in the 1990s the coverage became quite comprehensive again. In 2004, the state science frameworks of only three states had standards concerned with human evolution.