Chapter six of Jane Halonen and Steven Davis' e-book, The Many Faces of Psychological Research in the 21st Century is entitled "Dr. Jekyll Meets Mr. Hyde: Two Faces of Research on Intelligence and Cognition" and written by Robert Sternberg. The chapter provides a great overview of the theories of and research in intelligence.

Chapter 6 can be found at http://teachpsych.org/resources/e-books/faces/script/Ch06.htm with The Many Faces of Psychological Research in the 21st Century at http://teachpsych.org/resources/e-books/faces/script/index.htm