Observations on Primate Aggression
From time to time in SMT310 we cover the progress of the "Human Genome Initiative", that
is, the project the goal of which is to sequence the human genome, to compare the sequences with
other species and to continue to ask the question "Just what is it that makes us human," in the
context of the sequences we find, their placement in the genome and their interactions with each
other. Often our assigned articles comment on the great sequence similarity of genes of dissimilar
species. But how about similar species? DNA sequence analysis shows that humans are so
similar to the two chimpanzee species that humans might be thought of as "the third chimpanzee,"
according to Jared Diamond. On the average, the human genome shows that humans and
chimpanzees share at least 98.5% of their DNA sequences.
The following extract comes from "African Genesis" by Robert Ardrey and the research notes
Carpenter. Both Ardrey and Carpenter are careful not to draw conclusions or to reach
generalizations which might be considered to be too anthropocentric. Still, lay people not
by the scholarly strictures of anthropology might find it amusing that some of the creatures
may remind them of people they know.
For an example of how such an [exceedingly aggressive] male may affect the workings of an
society--in this case, a nonpredatory one--we must turn to the studies of C. R. Carpenter, and
more inspect the record of the rhesus monkeys transported from India to Santiago Island. Among
the generalizations which one may tentatively put forward concerning tendencies in animal
none rests more firmly on universal observation than Carpenter's own conclusion, that faced by
territorial invasion the home team almost always wins. Warfare can be, and must be, continuous
territorial boundaries. Hostility for one's neighbour must be unremitting, and when one meets him
the fence line one must give every evidence of intended rape, pillage, and bloodiest invasion. But
when the shouting is all over and perhaps a skull cracked here and there, it is the rule that both
retire where they came from.
We cannot say that conquest never occurs in the world of animals. Our studies are too
and have been so far too hit-or-miss to state that permanent conquest is a type of behaviour
solely to that species currently most eminent in world affairs. A family of gibbons, we know, will
conduct a grape raid into a neighbouring arboreal pasture; and a hawk, if he can get away with it,
sneak an occasional titbit from the next hawk's mouse field. But such disorderly conduct in the
of animals seems with rare exceptions directed towards an immediate objective with rapid
in mind from the beginning. The fundamental rights of territory are honoured even when they are
being violated. Despite our incomplete knowledge of animal affairs, one would be sorely tempted
state flatly that territorial conquest is a mode of animal behaviour so sporadic as to be of no
evolutionary significance, were it not for an exception so carefully observed and so carefully
as to causes, that one can only conclude that conquest as man knows it must occur in the animal
world when conditions properly combine.
The rhesus monkeys transported from India, we will recall, were about three hundred and
number; went to pieces morally on the voyage; and, resettled on the little Puerto Rican island,
about a year divided their thirty-six acres into territories, established their societies and regained
self respect. In the light of what happened later one must keep in mind that these territories were
and perhaps lacked to a degree the authority over behaviour that older territories might exert. If
was so, however, it was not reflected in rhesus behaviour. Each group quickly established its
hostility for neighbouring groups, and in customary isolation quickly welded its social life into an
amiable, xenophobic whole.
One of the objects of Carpenter's study was dominance. He had developed in the course of
primate studies certain criteria for dominant behaviour: how often one male would be the leader in
a move towards a new feeding place, and how often another; which made the first move towards
in the morning, and which towards rest at night; which took the lead in territorial disputes, or
the first call in an emergency. Such criteria compiled in the dossier of each male in a single society
gave in sum the individual's rank order in the hierarchy. And it told more. It gave one an index of
relative dominance that could be applied to a whole species. Primates are not like jackdaws. There
is no rigorous rank order in which every individual must always assume the same status in relation
to every other individual. In primate societies there is simply a tendency for one male rather than
another to take leadership in situations. Among gorillas that tendency is at its peak, so that one
rules and is never disputed. Among baboons the tendency is strong; a few males in the troop will
make almost all the decisions, and the dominant rank of one male in relation to another will be
distinct. The howler, for all his violent vocabulary, asserts the least rank in relation to his fellows.
is the closest to a co-operative, live-and-let-live, equalitarian society to be found in the primate
The rhesus monkey falls somewhere between the baboon and the howler. In a normal society
containing half a dozen males, Number One will take the lead or win the argument on perhaps
or five times as many occasions as Number Last. And Carpenter found the ratio of dominance in
transported rhesus society on Santiago Island to be of such a moderate sort, differing little from
of untransported rhesus societies which he had studied in India and Siam. But while he was
his various groups and making his calculations of dominance, an astonishing event took place.
Group I embarked on conquest. Group I seemed no different from any other troop on the
was average in size and contained the normal distribution of males, females, juveniles, and infants.
Its territory was of the same order of magnitude, and the food supply which as I have mentioned
distributed daily by a caretaker--was equally available to all. No reason for systematic aggression
could at first be discovered. But conquest nevertheless occurred. Daily Group I infringed on its
neighbours--and got away with it. Daily, regularly, Group I made its feeding excursions on to the
territories of not just one but five neighbouring societies. Group I was opposed, as it had to be
opposed, by the injured societies. There was no weakness in the opposition. But Group I by some
mysterious power broke that most fundamental of animal laws, that the home team wins. In this
the home teams, all of them lost; and Group I had its way on opposition territory. The mystery,
however, became quickly solved.
GROUP I contained a male of almost unbelievable dominance. He was Number One, of
his factor of dominance as compared to Number Last was about fifty. While a normal maximum in
the rhesus would be about five, Number One had as great an advantage as that even over Number
Two. That all powerful natural accident, conception, had placed in the genes of a remarkable
such resources of strength, of energy, of courage, and of assurance that he had become a giant of
dominance. And his very presence in a society amazingly enough communicated to all members of
the society the resources of his nature. Group I was pervaded by its leader's character, and despite
all laws of territorial behaviour acquired the capacity, as a society, to dominate its neighbours.
Carpenter removed the master monkey from the master society. The troop immediately fell
its own territory. Not once during the exile of its leader did the society commit a single act of
trespass. Then Carpenter restored the monkey to his fellows. Without hesitation Group I returned
its field of conquest. I find it difficult to review Dr. Carpenter's careful study without recalling
enigmas of the lion and of man. Nowhere in all the unexplored jungle of animal behaviour does
observer catch more fleeting glimpses of profound, suggested truths than along the shadowed
of animal dominance. So little do we truly know that observations are frequently little but hints. A
movement is reflected in a still pool; but when we look up, nothing is there. A face peers at us
the depths of a vine; but when we stir the leaves, the face is gone. We may say with certainty that
instinct for hierarchy benefits many an animal society.
Here is a description of the colony by Carpenter:
The field work for this report was done on Santiago Island, a small Cay of about 37 acres
five-eighths of a mile off the Southeast coast of Puerto Rico. The nearest point on the mainland is
Playa de Humacao and it is from there that boats leave to cross the narrow channel to the Island.
topography of Santiago Island is irregular. Its surface is covered by a cocoanut palm grove, scrub
trees, grass and weeds, rocks and new plantings of shade, fruit and ornamental trees. The Island
a situation which, in many respects, is uniquely favorable for a breeding colony of Rhesus
Here according to original plans, field and laboratory research were to be closely integrated.
The original stock of the Santiago Colony was collected by the author in India during
1938. Three months later, 409 monkeys were released on Santiago Island. On March 1, 1940 the
Rhesus Colony had about 350 monkeys in various stages of development ranging from infancy to
senility. There were 24 adult males and four sub-adult males who lived in heterosexual groupings,
while 12 subadult males lived in unisexual male groupings, thus making a total of 40 males in the
Colony. There were approximately 150 adult females, making a ratio of more than 6 adult females
to each adult male. In addition there were 3 sub-adult females, 48 infants born in India during July
and August, 1938,90 infants born in the Colony between May 19 and December 31, 1939 and
infants born since January 1, 1940.
Besides these Rhesus monkeys there was a male, a female and an infant of the pig-tail type
nemestrinus) constituting a small family. The animals organized themselves into 6 heterosexual
ranging in size from 3 in the case of the pig-tail group to 147 for the largest Rhesus group. The
smallest heterosexual Rhesus group had 13 individuals. The average Rhesus group contained
approximately 70 animals. This report is based on observations of 40 different Rhesus females of
Colony who passed through 45 periods of sexual receptivity between February 29 and April
When this study began the Rhesus Colony had just been released from isolation cages, in which
had been held for six weeks for tuberculosis testing.