How Many Friends Does One Person Need?
Dunbar’s Number and Other Evolutionary Quirks
Harvard University Press Cambridge, Massachusetts 2010
Copyright © 2010 by Robin Dunbar All rights reserved Printed in the United States of America First published in 2010 in the United Kingdom by Faber and Faber Limited Library of Congress Cataloging-in-Publication Data Dunbar, R. I. M. (Robin Ian MacDonald), 1947– How many friends does one person need? : Dunbar’s number and other evolutionary quirks / Robin Dunbar. p. cm. Includes index. ISBN 978-0-674-05716-6 (cloth : alk. paper) 1. Social psychology. 2. Human behavior. 3. Evolution. I. Title. HM1033.D857 2010 599.93′8—dc22 2010029306
Acknowledgements 1 In the Beginning 2 The Monogamous Brain 3 Dunbar’s Number 4 Kith and Kin 5 The Ancestors that Still Haunt Us 6 Bonds that Bind 7 Why Gossip is Good for You 8 Scars of Evolution 9 Who’d Mess with Evolution? 10 The Darwin Wars 11 So Near, and Yet So Far 12 Farewell, Cousins 13 Stone Age Psychology 14 Natural Minds 15 How to Join the Culture Club
1 3 11 21 35 47 61 73 85 99 113 127 143 161 175 191
How many friends does one person need?
16 Be Smart . . . Live Longer 17 Beautiful Science 18 Are You Lonesome Tonight? 19 Eskimos Rub Noses 20 Your Cheating Heart 21 Morality on the Brain 22 How Evolution Found God Index
203 215 227 243 253 267 279 293
This volume had its origins in a series of popular science articles that I wrote for New Scientist magazine (mostly between 1994 and 2006) and the Scotsman newspaper (between 2005 and 2008). In bringing them together in this volume, my intention has been to give some flavour of the excitement – and some of the fun – that has pervaded the evolutionary study of behaviour, and in particular human behaviour, over the last decade. I am grateful to both for providing me with an opportunity to indulge a passion for popular science writing over the years, as well as for allowing me to reuse these pieces in this volume. I also thank the Observer, Scotland on Sunday, the Times Higher Education Supplement, the Royal College of Physicians (London), Charles Pasternak and OneWorld Books, and Faber and Faber for permission to reuse individual pieces published by them. Most of these pieces have been substantially edited or adapted for this volume. Pieces published in the Scotsman make up the bulk of chapters 2, 4, 5, 8, 9, 10, 12, 13 and 16, and feature in chapters 3, 6, 11, 14, 17, 19 and 21. Pieces published in New Scientist magazine appear in chapters 7, 13, 14 and 21, and make up the bulk of chapters 3, 17, 18, 20 and 1
How many friends does one person need?
22. A piece published in the Observer contributes to chapter 7, and one from Scotland on Sunday to chapter 21. An article from the Times Higher Education Supplement makes up the bulk of chapter 15. Part of chapter 3 appeared in The Science of Morality (2007; edited by G. Walker, published by the Royal College of Physicians, London); part of chapter 12 originally appeared in my The Human Story (2004, Faber and Faber); and part of chapter 15 appeared in What Makes Us Human (2007; edited by Charles Pasternak, published by OneWorld Books, Oxford). Finally, I am grateful to my agent Sheila Ableman, and to my editor at Faber, Julian Loose.
In the Beginning
We share a history, you and I. A history in which our respective stories snake back through time, edging ever closer to each other until finally they meet up in a common ancestor. Perhaps our lineages meet up only a few generations back, or maybe it was a thousand years ago. Perhaps it was so long ago that it predates history – though even that could not have been more than two hundred thousand years ago, a mere twinkle in earth time. For we modern humans all descend from a common ancestor who roamed the plains of Africa a mere ten thousand generations...