Many people wittingly or unwittingly helped me in the writing of this book. For conversations, ideas, suggestions and material support I would like to thank Dave Byrne, Joan Chandler, Ken Connolly, Neil Cooper, Steve Fuller and Matt Treadwell. Dave Byrne, Elizabeth Ettorre, Robin Hendry, Liz Hodgkinson, Tim May and two anonymous referees read various chapters and made many helpful recommendations. Especial thanks to Tim for his encouragement, to Robin who saved me from too many scientific faux pas (though of course the responsibility for particular interpretations, or remaining errors, is mine alone) and to Liz, John and Laura for their love and support. Finally I would like to express my gratitude to Mari Shullaw, Ruth Graham, Shankari Sanmuganathan and the production team at Routledge for guiding this book from idea to actuality.