It is reassuring to know that virtually all researchers in a given field agree on something. In the field of intelligence, there are three facts about the transmission of intelligence that virtually everyone seems to accept.

1. Both heredity and environment contribute to intelligence.

2. Heredity and environment interact in various ways.

3. Extremely poor as well as highly enriched environments can interfere with the realization of a person's intelligence, regardless of the person's heredity.

Beyond these three facts, there is much divergence of opinion. We have edited this book in order to explore this divergence. Although there are certainly other books on the topic, we believe that, as of the book's publication date, no other volume is as up-to-date, balanced in its coverage of alternative views, and graced by the contributions of such a distinguished cast of authors, all of whom have been leading contributors to the field.

This book is for everyone who is interested in the question of how intelligence is transmitted: students, scholars, and curious laypersons. Authors were asked to contribute chapters that were technically sound and rigorous but that would nevertheless be interpretable to a wide variety of readers. We believe that the contributors fulfilled this mission.

Although we, as editors, have our own opinions and as authors have expressed these opinions, we have scrupulously tried to avoid favoring any one point of view.