The provenance of this book was a Dahlem workshop held in West Berlin in February 1978. Unlike most symposia, no lectures were given. Selected participants were asked to write background articles providing a review of their own particular aspect of the subject. These were intended to be provocative as well as informative. They were circulated to the other participants and questions formulated before the meeting so that detailed discussions could begin, forthwith.
It is clear that the participants were carefully chosen and that each was of high repute in his own discipline. They ranged from cell biologists, embryologists, experimental physiologists, and agriculturalists to research workers and clinicians working mainly in obstetrics and pediatrics.
The structure of the workshop was such that after the opening plenary sessions, four separate groups were formed to discuss different aspects of the subject. Each group presented a report at the end of the meeting.