Tree of Origin: What Primate Behavior Can Tell Us about Human Social Evolution

297 Pages·2001·80.38 MB·English

by  Frans B. M. de Waal

TREE OF ORIGIN
What Primate Behavior
Can Tell Us about
Human Social Evolution
Frans B. M. de Waal,
Editor
HARVARD UNIVERSITV PRESS
Cambridge, Massachusetts, and London, England
Unless othenvise noted, illustrations by Margaret C. Nelson
Copyright © 2001 by the President and Fellows of Harvard College
AU rights reserved
Printed in the United States of America
Designed by Marianne Perlak
Second printing, 2002
First Harvard University Press paperback edition, 2002
Library o/Congress Cataloging-in-Publication Data
Tree of origin: what primate behavior can tell us about hwnan social evolution /
Frans B.M. de Waal, editor.
p.em.
Includes bibliographical references and index.
ISBN 0-674-00460-4 (cloth)
ISBN 0-674-01004-3 (pbk.)
1. Primate Behavior. 2. Human evolution. 3. Social evolution.
I. Waal, F. B. M. de (Frans B. M.), 1948-
QL737.P91752001
599.8'15-dc21 00-050581
~-\l@@)u
2005/08
Contents
Frans B . M . de Waal
Introduction 1
1
Anne E . Pusey
Of Genes and Apes: Chimpanzee Social Organization
and Reproduction 9
2
Frans B. M. de Waal
Apes from Venus: Bonobos and Human Social Evolution 39
3
Karen B. Strier
Beyond the Apes: Reasons to Consider the Entire Primate Order 69
4-
Craig B . Stanford
The Ape's Gift: Meat-eating, Meat-sharing,
and Human Evolution 95
S
Richard W. Wrangham
Out of the Pan, Into the Fire: How Our Ancestors' Evolution
Depended on What They Ate 119
6
Richard W. Byrne
Social and Technical Forms of Primate Intelligence 145
7
Robin I. M . Dunbar
Brains on Two Legs: Group Size and the Evolution of Intelligence 173
8
Charles T. Snowdon
From Primate Communication to Human Language 193
!J
William C. McGrew
The Nature of Culture: Prospects and Pitfalls
of Cultural Primatolo81J 229
Notes 257 Contributors 301
Bibliography 277 Index 303
Frans B. M. de Waal
Introduction
I T IS READILY APPARENT that comparisons between humans and other
animals take two basic forms, depending on whether the main objec
tive is to confirm human identity or to stress the common thread that
fillS
through all forms of life. The first approach is still commonplace in the
social sciences and the humanities, where the importance of any particu
lar subject is underlined by claims that ours is the only species to which
the topic could possibly apply. The second approach-at least as old
received strong impetus from Darwin's theory of evolution by natural se
lection. Especially in the last couple of decades, the view of human behav
ior as the product of evolution, hence subject to the same explanatory
framework as animal behavior, has gained ground and respectability. It
has been transformed from a controversial minority view to one that today
is widely applied.
This transformation was made possible by major theoretical develop
ments in the field of animal behavior-such as the explanations of cooper
ative behavior at the heart of sociobiology and behavioral ecology-and by
the courage of a few scientists who in the 1970s began sending wake-up
calls to those sections of the academic community traditionally favoring
nurture over nature.
The evidence for a connection between genes and behavior is mow1t
ing rapidly. Twins-reared-apart studies have reached the status of com
mon knowledge, and almost every week newspapers report a new human
gene-those involved in schizophrenia, epilepsy, and Alzheimer's disease,
even in behavioral traits such as thrill-seeking. We are also learning more
about genetic and neurological differences between men and women. Not
that there is a simple one-on-one relation between genes and behavior: our
sound-bite culture tends to tum findings into a gene-for-this and a gene
for-that language, whereas in reality behavioral variability is only partly
explained by genetic factors (the other part being attributable to the envi-
1
2 . Frans B. M. de Waal
ronment}. Nevertheless, the list of scientific advances implying genetic in
fluences is getting longer by the day, resulting in a critical mass of evidence
that is impossible to ignore. Understandably, academics who have spent a
lifetime condemning the idea that biology influences human behavior are
reluctant to change course, but they are being overtaken by the general
public, which seems to have accepted that genes are involved in just about
everything we do and are.
Another development that has influenced the way we look at our place
in nature, and that has particular relevance to the present volume, is the
proliferation of research on monkeys and apes. In terms of genetics, neu
rology, cognition, and social behavior, many cherished assumptions in
support of human/ animal dualism have fallen by the wayside. DNA shld
ies have placed the apes far closer to us than anyone deemed possible at
the beginning of the twentieth cenrury. Not only are chimpanzees and
bonobos genetically our closest relatives, the reverse is also true; that is,
chimpanzees and bonobos are closer to us than to, say, gorillas.
•
Millions of Years Ago
o
35 30 25 20 15 10 5
I I I I I I I I
Hwnans
Chimpanzees
~~-:"'- Bonobos
Gorillas
Orangutans
()Id World Printates Old World Monkeys
~~------------~~----------~~---------Baboons
Macaques
......
""-=~--- Capuchins
MlUiquis
Squirrel Monkeys
Figure 1.1 Evolutionary tree showing the main branches of the primate order (ex
cept for the prosimians): the New World monkeys, the ()Id World monkeys, and the
hominoid lineage that produced our own species. The diagram reflects advances in
DNA analysis that place the African apes (gorillas, bonobos, and chimpanzees)
much closer to hlUl1ans than previously suspected.
Introduction . 3
People have a tendency to lump all two hUlldred primate species Ullder
the rubric of "monkeys," but the great apes (only four species: chimpan
zee, bonobo, gorilla, and orangutan) together with gibbons and humans
are a distinct group, the Hominoids, not to be confused with the Old World
monkeys (such as baboons and macaques), which in turn are not to be con
fused with New World monkeys (such as capuchins and marmosets). Fig
ure I.1 and Table I.1 offer help with the classification. Readers are referred
to MacDonald (1984) and Napier and Napier (1985) for more detailed pri
mate taxonomies.
So, after a period in which human behavior has been freely interpreted
in light of what we know about pigeons (such as the research of the learn
ing psycholOgist B. F. Skinner), geese (Konrad Lorenz), social insects (E. O.
Wilson), and rodents (Robert Ardrey, who compared people in inner cities
with crowded rats), comparisons increasingly focus on species that are a
lot closer and more similar to us than any of the above.
Such comparisons have captured public attention ever since Desmond
Table 1.1 The hominoid family is characterized by flat chests, rotational ability in
the shoulders, absence of tails, and relatively large body size. It includes
the Asian gibbons and siamangs (the so-called lesser apes), the
Pongidae (great apes) of Africa and Asia, and modern humans. With
the exception of the gibbon family, this table delineates the species and
subspecies of extant humans and apes, customarily divided into five
different species belonging to four genera.
Genus Species Subspecies Common name
Gorilla gorilla beringei Mountain gorilla
graueri Eastern lowland gorilla
gorilla Western lowland gorilla
Pongo pygmaeus pygmaeus Bornean orangutan
abelii Sumatran orangutan
Pan troglodytes verus Masked or pale-faced dlimpanzee
(west Africa)
troglodytes Black-faced chimpanzee (central
Africa)
seh weinfurthii Long-haired chimpanzee (eastern
Africa)
paniseus Bonobo (previously: pygmy
chimpanzee)
Homo sapiens sapiens Modern human
4 . Frans B. M. de Waal
Morris in 1967 published The Naked Ape, followed in 1971 by Jane Good
all's In the Shadow of Man. Both books relied on direct ape-human compari
sons-the former from the human perspective; the second, more subtly, via
an in-depth account of chimpanzee social life with the implicit message
that these animals are a great deal like us. These two early books are only
the tip of the iceberg, however. A steady stream of scholarly and popular
publications have appeared since, detailing numerous parallels between
human and ape behavior. Often the implication has been that these paral
lels represent homologies; that is, they derive from the common ancestor
of humans and apes. Some of the contributors to the present volume have
been in the forefront of this literature.
The growing influence of primate research has forced lingUists to look
more closely at their definitions of language, and anthropologists to con
sider nonhuman culture. Ape studies have also triggered the current fasci
nation with self-awareness and so-called Theory of Mind in child psychol
ogy. Even the origins of human politics, warfare, and morality are now
being discussed in the light of primate observations.
What is the objective of such comparisons? Is it just to show that we are
not alone in being cognitively and SOcially complex, or does it go deeper?
If humans and other primates show similar behavior, does that make the
apes look smarter, assuming that they put as much cognition into their ac
tions as we do? Or does it make us look dumber? Do similarities prove that
we are instinctive creatures held on a leash by our biology? These are the
sorts of questions that fueled many debates in the 1970s. There were accu
sations directed at biologists of genetic determinism and questions about
their application of human concepts to animal behavior (for instance, Sher
wood Washburn's 1978 essay "What We Can't Learn about People from
Apes"). The current generation of primatologists, however, is quite averse
to attempts to squeeze behavior into a simple "learned versus innate" di
chotomy. We assume that all behavior in all primates, including our own
species, derives from a combination of evolved tendencies, environmen
tal modification, development, learning, and cognition. The word instinct,
with its connotation of a purely genetic derivation, has indeed become out
dated except in usage such as a "language instinct," where the concept has
been broadened to stand for learning predisposition.
In sum, this book is not about our species as a preprogrammed robot
destined by its biology to act one way or another. The contributors have far
too high an opinion of the behavioral flexibility of their primary research
Introduction . 5
subjects, which in all cases are nonhuman primates, to embrace such a
view. If they see monkeys and apes as mentally complex, socially skilled,
even cultural beings, why would they want to simplify human behavior?
Rather, the goal is to understand human social evolution from the per
spective of what we know about the social organization, commwlication,
learned habits, subsistence, reproduction, and cognition of other extant
primates. This is no simple task, and it certainly has no simple answers.
The genesis of our book goes back to October 1997, when a conference
on Human Evolution was held at the well-known Cold Spring Harbor
Laboratory in New York State. A well-attended and well-received session,
organized by the writer, was entitled "Primate Behavior and the Recon
struction of Human Social Evolution." Six of the nine contributors to this
volume participated. All the other sessions, except for one on paleontol
ogy, dealt with molecular genetics.
It was felt that a symposium topic such as primate behavior deserved its
own volume; not since Warren Kinzey's 1987 book, The Evolution ofH uman
Behavior: Primate Models, has anyone brought together primatologists spe
cificallyarOlmd the question of human evolution. Most primatologists stay
close to their data without venturing too far into speculation about the ori
gins of human behavior. Even if some of our contributors are known ex
ceptions, there are no works juxtaposing their views with those of others.
In putting this volume together, we followed three simple rules:
1. All authors are behavioral primatologists-psychologists, anthropolo
gists, or zoologists extensively familiar with the behavior of monkeys and
apes. Informed opinions about human evolution are to be fOlmd in many
quarters (neuroscience, paleontology, linguistics), but we wished to pre
sent the primate perspective straight from the pen of people with intimate,
firsthand knowledge of the natural or naturalistic behavior of this special
taxonomic group.
2. All contributors speculate about the origins of human evolution. How
is our species similar to or different from other primates, and which selec
tion pressures may have forced our ancestors to evolve in the direction
they took. Some authors address this issue more explicitly than others, but
all present an aspect of what primate behavior can tell us about human so
cial evolution.
3. Contributors were asked to write in an accessible, jargon-free style.
Only the notes provide technical background. The authors should be for-
6 . Frans B. M. de Waal
given for not citing each and every relevant study, and for not mentioning
every angle of a problem. Even though all contributors are recognized ex
perts in their field, there is no mainsh·eam view on the topic of human evo
lution. Hence this book should be supplemented with other readings, in
cluding altemative views by other scholars.
No attempt has been made here to reconcile differences of opinion. It
would be surprising if any treahnent of this topic at this stage could pro
vide lasting answers. Our hope, rather, is that this book will make readers
rethink hlUnan evolution, and consider peculiarities of our species or lines
of argument that they have not taken into account before. Even if what one
author considers obvious is questioned by another, it is the underlying
problem that matters most.
For example, Robin Dunbar follows many other primatologists in argu
ing for social complexity as the driving force behind the evolution of intel
ligence, whereas Richard Byme thinks that, at least in the apes, planning of
action chains played a significant role-and Craig Stanford sees the poli
tics surrounding meat-sharing as yet another factor. All three authors try
to come up with reasons why primate brains expanded so much more, rel
ative to body size, than the brains of other land mammals. The reader need
not choose among these points of view to recognize that an evolutionary
explanation is needed, which at the same time may tell us something about
our own species, which has the largest brain of all.
Other differences of opinion are evident too. Richard Wrangham regards
the chimpanzee as the best model of the last common ancestor of hun1ans
and apes, whereas Frans de Waal argues that the bonobo is at least as good
a candidate. Stanford emphasizes hunting and meat-sharing in human
evolution, in contrast to Wrangham's focus on plant foods. Charles Snow
don looks for continuities between primate communication and human
language, whereas Dunbar emphasizes the social bonding function of lan
guage and places it functionally closer to grooming. Finally, whereas many
authors emphasize the behavior and cognitive capacities of our closest rel
atives, Karen Strier urges us to look beyond the apes.
This final point relates to two different approacl1es to the matter of hu
man evolution. One involves development of general principles that apply
to a great variety of species, from insects to birds to humans. Primates are a
not particularly numerous or varied group of organisms to consider when
we investigate how the distribution of food affects social organization, or
the conditions under whicl1 animals increase in body size, or how competi-