When we began this series we wanted to encourage imaginative thinking among ethologists and those working in related fields. By the time we had reached Volume 3, we were advised by our publishers to give each volume a theme. Although we accepted the advice, it ran somewhat counter to our own wish to give our authors full rein. It also meant that we could not accept submitted manuscripts if they lay too far outside the topic for the next volume. We did, however, cheat a little, and faithful followers of the series will have noticed that some of the contributions were not exactly on the stated theme. Anyway, our publishers have now agreed that we can make honest people of ourselves by once again ac cepting a broad range of manuscripts for any volume. We shall also solicit manuscripts on particular topics that seem to be timely and appropriate, and each volume will continue to have a subtitle that relates to the theme of the majority of the papers in the volume. We hope that with our more permissive policy now explicit, potential contributors will feel encouraged to submit manuscripts to either of us at the addresses given at the end of this Preface. When planning the present volume, we wanted our contributors to build bridges between studies of behavior and the neurosciences. In recent years, the majority of people working on behavior seem to have been exclusively concerned with functional and evolutionary approaches.