Table Of ContentGAS T E AND EC OLO G Y
IN THE
Social Insects
MONOGRAPHS IN POPULATION BIOLOGY
EDITED BY ROBERT M. MAY
1. The Theory of Island Biogcography, by Robert II. MacArthur
and Edward O. Wilson
2. Evolution in Changing Environments: Some Theoretical Ex-
plorations, by Richard Levins
3. Adaptive Geometry of Trees, by Henry S. Horn
4. Theoretical Aspects of Population Genetics, by Motoo Kimura
and Tomoko Ohta
5. Populations in a Seasonal Environment, by Stephen D. Fretwell
6. Stability and Complexity in Model Ecosystems, by Robert M.
May
7. Competition and the Structure of Bird Communities, by Martin
Cody
8. Sex and Evolution, by George C. Williams
9. Group Selection in Predator-Prey Communities, by Michael E.
Gilpin
10. Geographic Variation, Speciation, and Clines, by John A. Endler
11. Food Webs and Niche Space, by Joel E. Cohen
12. Caste and Ecology in the Social Insects, by George F. Oster and
Edward O. Wilson
CASTE AND ECOLOGY
IN THE
Social Insects
GEORGE F. OSTER AND
EDWARD O. WILSON
PRINCETON, NEW JERSEY
PRINCETON UNIVERSITY PRESS
1978
Copyright (c) 1978 by Princeton University Press
Published by Princeton University Press, Princeton, New Jersey
In the United Kingdom: Princeton University Press, Guildford,
Surrey
ALL RIGHTS RESERVED
Library of Congress Cataloging in Publication Data will be
found on the last printed page of this book
This book has been composed in Monophoto Baskerville
Clothbound editions of Princeton University Press books are
printed on acid-free paper, and binding materials are chosen for
strength and durability.
Printed in the United States of America by Princeton
University Press, Princeton, New Jersey
TO THE MEMORY OF
Aharon Katzir-Katchalsky
Preface
This monograph is not intended to be a finished treatise on
the theory of castes in social insects. Rather, it is a prole-
gomenon—a beginning effort to make some sense out of the
veritable mountain of empirical findings gathered by hun-
dreds of investigators over decades of research. By focusing
attention on the ecological and evolutionary aspects of caste,
as distinct from developmental and physiological processes,
we hope to provide the beginnings of a unifying theoretical
framework.
When we first conceived the idea of developing a "theory
of caste" the task seemed manageable. Here was a neat, cir-
cumscribed evolutionary puzzle that had troubled biologists
since Darwin. Moreover, the empirical data, while voluminous,
seemed to hint at an underlying simplicity. Perhaps, with a
bit of luck and cleverness, we could find the "answer"—a
single new way of looking at the problem that would disclose
the raison d'eHre of caste polymorphism in social insects and
cause all the data to fall into place. This conceit was shortlived.
The deeper we delved the more we came to see the phenomenon
of caste structure as a microcosm for much larger evolutionary
issues in sociobiology.
The most important realization that changed our view was
the observation that caste polymorphism represents but one
evolutionary strategy to enhance ergonomic efficiency. An
equally potent strategy is "behavioral flexibility." Indeed,
once a species adopts sufficiently complex individual behavior
that can respond to fluctuations in the environment, selective
forces promoting physical polymorphism are largely neu-
tralized. Thus, of all the 263 living ant genera, only 44 contain
species that display any prominent degree of polymorphism
within the worker caste; the others clearly have been able to
PREFACE
do without it. The ultimate reason why a species takes the
evolutionary road to physical polymorphism may be im-
ponderable. Indeed, current evolutionary thought gives a
much larger role to historical accident than in the past. The
function of science is to explain what can be explained, not
what should be explained.
Therefore, the most that can be accomplished from evo-
lutionary retrospection might be to characterize the agents
of natural selection that promote one or the other of multiple
strategies. The best way of doing this, in our view, is to construct
quantitative models. The reason quantification is necessary is
the ambitendent nature of the evolutionary process. As we
shall stress repeatedly throughout this book, the direction of
evolutionary change is the result of conflicting adaptive re-
quirements. The optimal adaptation is almost always a com-
promise between selective forces whose magnitudes are
commensurable. Thus, evolutionary problems can seldom be
resolved by verbal arguments alone, except in exceptional
instances where there is a single overwhelming selective force.
In most cases, it is not a question of which forces operate, since
their effects are manifest, but rather of their relative magnitudes.
The evolutionary solution reached by a species is a quantitative
rather than a qualitative problem. For this reason we have
chosen to organize the entire book around a series of mathe-
matical models, which are conceived to have two purposes:
(1) to provide an unambiguous conceptual structure for the
theory, and (2) to serve as a guide for future empirical research.
Like most biologists concerned with theory, we appreciate
that models do not themselves provide definitive answers to
biological questions. Mathematics is, after all, little more than
scaffolding upon which all manner of facts about the real
world can be arranged, hopefully into a more esthetic and
useful structure. Mathematical theory is the science of all
conceivable worlds. The most important role models play in
