The Explosive Growth and Demise of a Mouse Population

80 Proc. roy. Soc. Med. Volume 66January 1973
peculiar to man allows for the learning of
language and social habits, and is undoubtedly
the result of selection of factors making for
delayed adolescence, enabling the more co-
operative groups ofpeople to survive.
It is an interesting question whether still closer
social co-operation might be achieved by a society
that adopted some method ofclonal reproduction
by which all men were truly brothers. Altruism is
an effective evolutionary policy only if it benefits
your own genes, and the ants and bees use very
special methods to ensure this. Technically such
changes begin to look almost possible; whether
they are desirable is another matter. We certainly
cannot foresee them in the near future, but the
possibility of them may remind us that the
biggest difference of all between men and animals
is in the vast range of techniques of control of
life that are now becoming available. We are all
familiar with the effects of the techniques of
physical science in promoting the industrial
revolution and the invention ofmachines. Perhaps
it is still insufficiently realized that biological
knowledge is now producing a still greater revolu-
tion, namely in the way we manage ourselves.
Inevitably the medical profession finds itself in
the forefront of this revolution and has to learn
to deal with all the new problems that it brings.
This symposium is especially welcome for that
reason. I should like to emphasize once more that
the problems are those of information and con-
trol. We shall collect much information today.
We shall probably not have much to say about
the problems ofhow it is to be used for the control
of human life. But I hope that we shall not forget
that if we are to achieve successful regulation in
the future we shall have to be ready to use and
to accept control in matters of population and
environment. The need for such control should
not alarm us, ifit is properly based on information
and feed-back. After all, it is a natural extension
of the regulation by the information of our DNA
or by the language and social customs that we
inherit from the past.
We should never forget that the continuation
ofour lives depends every moment on information
from the past. We are as we are because of the
endowment we receive, particularly from our
genes, our language and our social system. With-
out them we are nothing. Life depends upon
regulation, and the opposite of control is death.
We should be thankful that we are subject to
genetic, linguistic and social systems that allow us
a full and developing life, however far it may be
from perfection, whatever that may mean.
Let us rejoice in the fact that we live at a time
when ever-fresh sources of information abound,
and when people are beginning to realize the need
for closer and closer co-operation for survival.
Death Squared:
The Explosive Growth and Demise
of a Mouse Population
by John B Calhoun MD
(Section on Behavioral Systems,
Laboratory ofBrain Evolution & Behavior,
National Institute ofMentalHealth,
9000 RockvillePike,
Bethesda, Maryland20014, USA)
I shall largely speak of mice, but my thoughts are
on man, on healing, on life and its evolution.
Threatening life and evolution are the two deaths,
death of the spirit and death of the body. Evolu-
tion, in terms ofancient wisdom, is the acquisition
of access to the tree of life. This takes us back to
the white first horse of the Apocalypse which with
its rider set out to conquer the forces that
threaten the spirit with death. Further in Revela-
tion (ii.7) we note: 'To him who conquers I will
grant to eat the tree' of life, which is in the
paradise of God' and further on (Rev. xxii.2):
'The leaves of the tree were for the healing of
nations.'
This takes us to the fourth horse of the
Apocalypse (Rev. vi.7): 'I saw ... a pale horse,
and its rider's name was Death, and Hades
followed him; and they were given power over a
fourth ofthe earth, to kill with the swordand with
famine and with pestilence and by wild beasts of
the earth' (italics mine). This second death has
gradually become the predominant concem of
modern medicine. And yet there is nothing in the
earlier history of medicine, or in the precepts
embodied in the Hippocratic Oath, that precludes
medicine from being equally concerned with
healing the spirit, and healing nations, as with
healing the body. Perhaps we might do well to
reflect upon another of John's transcriptions
(Rev. ii. 1): 'He who conquers shall not be hurt
by the second death.'
Bodily Mortality
Let us first consider the second death (Table 1).
The four mortality factors listed in Revelation
have direct counterparts (with a division of one
of them to form a total of five) in the ecology of
animals in nature. I shall briefly treat each of
Table 1
The second death
As in Revelation vi.8 Ecologicalexpression
(1) Sword (1) Emigration
(2) Famine (2a) Resource shortage
(2b) Inclement weather
(and fire and cataclysms
ofnature)
(3) Pestilence (3) Disease
(4) Wild beasts (4) Predation

Symposium on Man in HisPlace
Fig 1 Universe 25, February 101970, 681 days after colonization. Calhoun in universe with an exceptionally
large aggregate ofpooledwithdrawn mice on thefloorjust across the centre ofthefloorfrom him. Note the
aggregation ofmice on somefoodhoppers in contrast to their near absence on others. This is the 'behavioural
sink'phenomenon in which the learnedneedforproximity to others as a secondary reinforcer at a
resource site gains dominance over theprimary need, in this casefood. Photo by Yoichi R Okamoto
these five mortality factors, and then discuss the
steps taken to eliminate, or drastically reduce, the
impact of each in a Utopian environment con-
structed for mice.
(1) Emigration: Animals in the wild rarely die
from the 'sword' directly; few are the deaths from
intraspecific combat. Rather it is that individuals,
who have failed in the more symbolic conflicts
involved in gaining the right to remain in the
locality of their birth or in more preferred
habitats, take recourse to movement into peri-
pheral unoccupied or suboptimal habitats. In
strange and less favourable habitats the emigres
become more exposed to other mortality factors.
Any removal of excess members from an estab-
lished population, from the point of view of
change in its numbers, represents mortality. In
this sense emigration is a mortality factor.
(2a) Resource shortage: Classically food and water
have received the focus of attention with respect
to their reduction increasing the likelihood of
death. Shortages of shelter, other environmental
resources and associates lead to debilitation, and
an unsatisfactoriness of habitat that culminate in
death or failure to reproduce (species death).
(2b) Inclement weather: Every species of animal
has developed a genetic adaptation to some
particular range of external conditions which
affect its physiology. Any conditions of wind,
rain, humidity or temperature which exceed the
usual limits of tolerance bring death immediately
or increase the risk of death through debilitation.
Beyond these more usual contributions to mor-
tality, flood and fire represent cataclysmic changes
that have widespread and more long-lasting effects
on population numbers.
(3) Disease: Although most animals develop some
capacity to tolerate the parasites, bacteria and
viruses that invade their bodies, most species still
remain subject to epidemic decimation in addition
to a more normal attrition from disease. Abnor-
mally high densities enhance the likelihood of
spread ofdisease to epidemic proportions.
(4) Predation: Practically every species has,
through evolution, had associated with it preda-
tors capable ofkilling some ofits members.
Despite loss of members from these five kinds
of mortality, most species persist over long
periods, even those measured in geological time.
To do so every such species has developed
81

capacities for reproduction requisite to compen-
sate for losses from the normal impact of
mortality factors other than ageing. I have
omitted senescence as a mortality factor since
rare is the animal who lives long enough in nature
to reach a post-reproductive age without having
succumbed to one of the above mortality factors.
A Mortality-inhibiting Environmentfor Mice
Some of the attributes of this environment have
been discussed or figured elsewhere (Calhoun
1969, 1971, Wigotsky 1970). Here I shall describe
how its design reduced mortality.
(1) Emigration prevention: A closed physical
universe was formed by four 54 inch (1.37 m)
high walls forming a square of side 101 inches
(2.57 m). Although the walls were structured for
use by mice to increase the effective use-area of
the universe, the mice could not climb over the
upper 17 inch (43 cm) unstructured portion of the
galvanized metal walls.
(2a) Resource supra-availability: Each 25j inch
(64 cm) linear segment of wall was identically
structured. Four 3 inch (7.6 cm) diameter tunnels
34 inches (86 cm) long of i inch (12.5 mm) mesh
wire were soldered vertically to the walls. The
open lower end, just above the floor which was
covered with ground corn cob, gave access to
each tunnel. At 8 inch (20.3 cm) intervals above
the floor in each tunnel four 1I inch (3.2 cm)
openings through the tunnel mesh and the metal
wall gave access to 8 x 5 x 4 inch (20.3 x 12.7 x
10.2 cm) retreat nesting boxes. Fifteen mice could
comfortably rest in a single nest box. Thus there
were four four-unit walk-up one-room apartments
in each cell. The cell is the replicated wall con-
figuration, here being described, with an asso-
ciated 640 sq. inch (0.356 m2) of floor space. A
wire mesh food hopper with a 6 x 10 inch
(15 x 25 cm) surface was located in each of the
16 cells halfway up the wall and in contact with
the right-hand tunnel of each set of four tunnels.
Mice climbing across the outer surface of the
tunnel gained access to the food hopper. Twenty-
five mice could feed simultaneously on a hopper.
By further climbing up the outside surface of the
tunnels mice had access to a 4 x 18 inch (10 x 45
cm) platform above which four water bottles were
suspended. Two mice could drink simultaneously
at each bottle. An abundant supply of paper
strips for nesting material was always available
on the floor a few inches out from the bases of
the tunnels. Considering the time required to eat
and drink, access to food would not have been a
limiting variable until a population of 9500 was
reached, or 6144 for water. Considering that there
were 256 nest retreat sites in the 16 cells one
would not expect shelter to be a limiting factor
until the population exceeded 3840. Due to the
tendency of many animals to choose to crowd
together in numbers in excess of 15 per nest site,
at the peak population size of 2200 mice, 20% of
all nest sites were usually unoccupied. Thus there
was always opportunity for females to select an
unoccupied space for rearing young if they so
chose.
(2b) Weather amelioration: The mouse universe
was located on the second floor of a prefabricated
metal building. During the cooler months of the
year ambient temperature was kept close to 68°F
(20°C). During the warmer months of the year
large exhaust fans kept ambient temperatures
mostly within the 70-90'F (21-32°C) range of the
outside environment. Being indoors, rain could
not contribute to debilitation. Air movement was
kept low, except when this favoured heat loss
during periods ofhigher ambient temperature. No
evidence was ever obtained to indicate that such
weather conditions enhanced mortality.
(3) Disease control: The Balb C albino house mice
(Mus musculus) used as colonizers in this study
were obtained from the National Institutes of
Health breedingcolony whereextreme precautions
are followed to preclude establishment of epi-
demic type diseases such as salmonella. Bacterial
culture taken at the highest density of the popula-
tion indicated that such organisms were not a
factor in our study. About every four to eight
weeks the ground corn cob in all nest boxes and
the floor was removed along with accumulated
feeces.
(4) Predation: No predators were present.
Some mortality did occur throughout the his-
tory of the population we initiated in this 16 cell
universe. Not until the mice became quite old did
the mortality from ageing contribute significantly
to removal of members from the population. On
the basis of initial analyses, menopause in females
comes at about 560 days ofage. Although we have
not yet determined the average life expectancy at
weaning, I suspect that it is well past menopause.
Large numbers of mice lived to 800 days of age,
which is equivalent to 80 years of age for a
human.
Explosive InitialPopulation Growth,
the Resource Exploitation Phase B
Four pairs of 48-day-old Balb C strain house
mice were introduced into the 16 cell universe on
July 9 1968, after each mouse had been isolated
for 21 days following weaning. There followed
a period of 104 days (Phase A) before the first
litters were born. These 104 days were marked
by considerable social turmoil among these 8 mice
until they became adjusted to each other and to
their expanded surroundings. Following this

UNIVERSE 25
Last Born, Mar,1970
DAC 736, N=2056*-_
DAC 560, N = 2200
DAC 315, N=620 776 Days
N- 150 Optimum No of Adults Mar, 1972
Phase Phase Phose
B C D
IU
An U AN
DYA T 1CA )THP
DAYS AFTER COLONIZATION (DAC) WITH 4 PAIR OF MICE
Fig 2 History ofpopulation ofmice in a closed Utopian universe.
Broken line represents an estimate ofnumbers made about 700 days
after colonization on the basis ofobserved mortality to
that time. Observedpoints after Day 1000 are slightly
lower thanprojecteddue to removalofabout 150 micefor other studies.
Afinalpoint was added to the graphfor Day 1471 when the population had
decreased to 100. Atfinal editing ofthispaper on November 13, 1972 (Day 1588)
the inexorable decline brought thepopulation to 27 (23females and
4 males, the youngest ofwhich exceeded987 days ofage)
adjustment and the birth of the first litters the
population exhibited an exponential increase, with
a doubling time of about 55 days (Fig 2). This
progression of numbers was approximately 20,
40, 80, 160, 320, to 620 after nearly five doublings.
I call this period of most rapid growth Phase B.
At 620 weaned mice the rate ofpopulation growth
abruptly decreased to a doubling time of approxi-
mately 145 days. Periodically through Phase B,
young born into the universe reached sexual
maturity and bore young, thus contributing to
the compound interest rate of population growth.
Distribution of place of birth (Fig 3) of mice
born during Phase B provides an insight into the
social organization that developed. The square
represents the wall of the pen, and the small black
rectangles depict the locations ofthe food hoppers
along its inner surface. Between each two hoppers
there are four sets of walk-up apartments, each
set containing four nest boxes accessible by a
single tunnel. The total young born in each of the
64 sets of four nest boxes were tabulated for the
period through the first survey after the termina-
tion of Phase B. These totals are shown in Fig 3
as open bars extending outward from the wall of
the pen.
It may be seen that births tended to be con-
centrated in some sets of nest boxes, while others
had few or none. This uneven distribution of
births reflects a clustering of reproducing females
into brood groups defined in Fig 3 by lines
radiating toward the centre of the universe from
the bases of nest boxes at the interface between
each two adjoining brood groups. Total births
per brood group are indicated between radial
lines. These totals reflect two properties of a
closed social system:
(1) Bilateral symmetry: The northeast brood
group produced only 13 young in 252 days
whereas the opposite southwest brood group
produced over eight times as many, 111. Between
these two extremes from the location of the peak
producing brood group toward the least pro-
ductive one, in both clockwise and counter-
clockwise directions, there is a decline in number
of young born. This trend reflects the attempt by
the members of the population to superimpose a
more effective bilateral symmetry of organization
UNIV. 25
DAC 86 TO 338
Fig 3 Production ofyoung between 86 and338 days
after colonization. Black rectangles represent location
offoodhoppers on inner surface ofwalls ofthe
universe. Bar graph represents number ofyoung born
in each verticalset offour nest boxes
IOGO.E
N4 -
100 -
10 -
IUO
83
U

UNIV 25 PUP PRODUCTION
DAC 86 TO 338
5 10
RANK OF NO, OF PUPS = X
Fig 4 Rank-frequency curve ofproduction ofyoung by
broodgroups. Number ofyoung in a broodgroup
reflects the degree ofdominance ofthe territorial
male associated with the broodgroup
upon an environment that tends toward radial
symmetry.
(2) Hierarchy ofgroups: Productivity of a group
may be taken as an index of its social status. The
fourteen brood groups may thus be ranked with
rank No. 1 assigned to the group which produced
111 young, and rank No. 14 to the one which
produced only 13 young. Plotting the number of
young produced as a function of this ranking
(Fig 4) reflects a remarkable hierarchical ordering
within the total social system. This type of order-
ing is identical to that which results when we
examine the degree of activity exhibited by the
several males of an interacting group. The most
dominant male is the most active one, and as
social dominance declines so does the degree of
activity. Such activity is termed 'social velocity'
(Calhoun 1963, 1967, 1971). Our studies show
that in a group of 14 males social velocity declines
linearly with rank with approximately the same
slope as in Fig 4. Each of the brood groups had
associated with it a male which was territorially
dominant within an area on the floor roughly
coinciding with the sectors shown in Fig 3. All
the ranges of these territorial males overlapped
near the centre of the universe. The most domi-
nant male was always associated with the brood
group that produced the most young, and the
degree of dominance of the other territorial males
tended to be reflected by the productivity of
females associated with them.
Both bilateral and hierarchical social organiza-
tion during Phase B contributed to a maximum
exploitation of resources that led to an explosive
rate of increase of the population. At the end of
this phase all the most desirable physical space
was filled with organized social groups. These 14
social groups totalled 150 adults. On average each
group contained over 10 individuals including a
territorial male, associated males and females,
and their juvenile and subadult progeny. At the
end of Phase B there were 470 of these immature
mice that had experienced good maternal care and
early socialization. Thus there were over three
times as many younger animals as the socially
established older ones. This number is far greater
than would have existed had the normal ecological
mortality factors functioned.
InhibitedSecondaryPopulation Growth,
the Stagnation Phase C
Beginning at Day 315 after colonization and con-
tinuing for 245 more days, the population grew
at a much slower rate, doubling only every 145
days rather than each 55 days as in Phase B. Let
us examine the circumstances surrounding this
decline in rate of population growth. In the
normal course of events in a natural ecological
setting somewhat more young survive to maturity
than are necessary to replace their dying or
senescent established associates. The excess that
find no social niches emigrate. However, in my
experimental universe there was no opportunity
for emigration. As the unusually large number of
young gained adulthood they had to remain, and
they did contest for roles in the filled social
system. Males who failed withdrew physically and
psychologically; they became very inactive and
aggregated in large pools near the centre of the
floor of the universe. From this point on they no
longer initiated interaction with their established
associates, nor did their behaviour elicit attack by
territorial males. Even so, they became charac-
terized by many wounds and much scar tissue as
a result of attacks by other withdrawn males.
Return of 2 or more males, who had gone to eat
and drink, marked an abrupt shift in the level of
ambient stimuli for their quiescent associates.
Resultant excitation often precipitated one of the
resting males into an attack upon his other with-
drawn associates who, having lost the capacity
for fleeing, remained relatively immobile despite
receiving vicious attacks. A mouse so attacked
would at a later time become an attacker.
Female counterparts of these withdrawn males
tended to withdraw to higher level boxes that
were less preferred by females with litters. Such
females were not charactetized by the violent
aggression ofthe withdrawn males.
As a result of the extreme demands made on
territorial males to reject maturing associates,
their ability to continue territorial defence
declined. Gradually the frequency of this involve-
ment in territorial defence declined as did the
area defended. This left nursing females more
exposed to invasion of their nest sites. Normally
nursing females in the presence of territorial
cr
CD
Ir
CD
*L-
w
Q-

males exhibit little aggression. However, in
response to invasion of nest sites and bases of
ramps leading to them, the nursing females did
become aggressive, essentially taking over the role
oftheterritorial males. This aggression generalized
to their own young who were attacked, wounded,
and forced to leave home several days before
normal weaning. During Phase C the incidence
of conception declined, and resorption of feetuses
increased. Maternal behaviour also became dis-
rupted. Young were often wounded in the delivery
process. Females transported their young to
several sites, during which process some were
abandoned. Many litters of a young age on one
survey disappeared before the next survey. Such
abandoning of young following survey distur-
bance is a particularly sensitive index of dissolu-
tion of maternal behaviour. The combined effect
of these several factors affecting reduced con-
ception, increased feetal mortality and increased
preweaning mortality largely accounts for the
abrupt decline in rate of population growth
characterizing Phase C. For all practical purposes
there had been a death ofsocietal organization by
the end ofPhase C.
Decline ofPopulation Size,
the DeathPhase D
Population increase abruptly ceased on Day 560
after colonization. A few mice born up until Day
600 survived past weaning. Between these times
deaths just slightly exceeded births. Beyond the
time of the last surviving birth on Day 600 the
incidence of pregnancies declined very rapidly
with no young surviving. Last conception was
about Day 920. With the increase in rate of
mortality accompanying senescence the popula-
tion has continued to decline in numbers. By
March 1 1972, the average age of survivors was
776 days, over 200 days beyond menopause. On
June 22 1972, there were only 122 (22 male, 100
female) survivors. Projection of the prior few
months of exponential decline in numbers indi-
cates that the last surviving male will be dead on
May 23 1973, 1780 days after colonization. The
population will be, reproductively, definitely dead
at that time, although such death was predicted
by 700 days after colonization. This demise of a
population contradicts prior knowledge which
indicates that when a population declines to a
few remnant groups, some individuals will
reinitiate its growth.
Turning back to the end of Phase C, the seeds
for eventual destruction may already be seen to
have been sown. By midway in Phase C essentially
all young were prematurely rejected by their
mothers. They started independent life without
having developed adequate affective bonds. Then
as they moved out into an already dense popula-
tion many attempts to engage in social interaction
were mechanically disrupted by passage of other
mice. Lastly, I have shown (Calhoun 1963) that
in proportion to the extent that the group size
exceeds the optimum, maximizing gratification
from such interactions necessitates a decrease in
the intensity and duration of such behaviours.
This fragments otherwise more complex be-
haviours. As a result of these three processes
(failure to develop early social bonding, mechani-
cal interference with developing social behaviours
and fragmentation of behaviours) maturation of
the more complex social behaviours such as those
involved in courtship, maternality and aggression
failed. For females a clear example may be taken
from a 2 cell universe studied in parallel with the
16 cell one detailed here. The members of this
population were killed 300 days after the inflec-
tion point of the shift from Phase C to Phase D.
Among these were 148 females born within the
last 50 days before the end ofPhase C. At autopsy
at a median age of 334 days only 18% had ever
conceived (i.e. no placental scars in the uteri of
82% of the females) and only 2% were pregnant
(each of these 3 females had only one embryo as
contrasted to the more normal 5 or more). By
this age most females in a normal population
would have had five or more litters, most of them
successfully reared.
Male counterparts to these non-reproducing
females we soon dubbed the 'beautiful ones'.
They never engaged in sexual approaches toward
females, and they never engaged in fighting, and
so they had no wound or scar tissue. Thus their
pelage remained in excellent condition. Their
behavioural repertoire became largely confined to
eating, drinking, sleeping and grooming, none of
which carried any social implications beyond that
represented by contiguity ofbodies.
Most of the last half of the population born in
the 16 cell universe were fully or largely like
these non-reproducing females and these 'beauti-
ful ones' (males). As their formerly more com-
petent predecessors gradually became senescent,
their already disrupted capacity for reproduction
terminated. At this time only the 'beautiful one'
category of males, and their counterpart females,
remained at an age normally compatible with
reproduction, but they had long since failed to
develop this capacity.
My colleague, Dr Halsey Marsden (1972), con-
ducted several studies during the mid-third of
Phase D in which he placed small groups of mice
out of these crowded populations into new
universes at very low densities. All groups
exhibited nearly total loss ofcapacity for develop-
ing a structured society or for engaging in the full
repertoire of reproductive behaviours. Even
placing them with adequate sex partners of the
85

opposite sex, that had matured in uncrowded
conditions, also gave very little indication of
retention ofany adequate reproductive behaviour.
Conclusion
The results obtained in this study should be
obtained when customary causes of mortality
become markedly reduced in any species of
mammal whose members form social groups.
Reduction of bodily death (i.e. 'the second death')
culminates in survival of an excessive number of
individuals that have developed the potentiality
for occupying the social roles characteristic of the
species. Within a few generations all such roles in
all physical space available to the species are
filled. At this time, the continuing high survival
of many individuals to sexual and behavioural
maturity culminates in the presence of many
young adults capable of involvement in appro-
priate species-specific activities. However, there
are few opportunities for fulfilling these poten-
tialities. In seeking such fulfilment they compete
for social role occupancy with the older established
members of the community. This competition is
so severe that it simultaneously leads to the nearly
total breakdown of all normal behaviour by both
the contestors and the established adults of both
sexes. Normal social organization (i.e. 'the estab-
lishment') breaks down, it 'dies'.
Young born during such social dissolution are
rejected by their mothers and other adult asso-
ciates. This early failure of social bonding
becomes compounded by interruption of action
cycles due to the mechanical interference resulting
from the high contact rate among individuals
living in a high density population. High contact
rate further fragments behaviour as a result of the
stochastics of social interactions which demand
that, in order to maximize gratification from social
interaction, intensity and duration of social
interaction must be reduced in proportion to the
degree that the group size exceeds the optimum.
Autistic-like creatures, capable only of the most
simple behaviours compatible with physiological
survival, emerge out of this process. Their spirit
has died ('the first death'). They are no longer
capable ofexecuting the more complex behaviours
compatible with species survival. The species in
such settings die.
For an animal so simple as a mouse, the most
complex behaviours involve the interrelated set of
courtship, maternal care, territorial defence and
hierarchical intragroup and intergroup social
organization. When behaviours related to these
functions fail to mature, there is no development
of social organization and no reproduction. As
in the case of my study reported above, all mem-
bers of the population will age and eventually die.
The species will die out.
For an animal so complex as man, there is no
logical reason why a comparable sequence of
events should not also lead to species extinction.
If opportunities for role fulfilment fall far short
of the demand by those capable of filling roles,
and having expectancies to do so, only violence
and disruption of social organization can follow.
Individuals born under these circumstances wilt
be so out of touch with reality as to be incapable
even ofalienation. Their most-complex behaviours
will become fragmented. Acquisition, creation
and utilization of ideas appropriate for life in a
post-industrial cultural-conceptual-technological
society will have been blocked. Just as biological
generativity in the mouse involves this species'
most complex behaviours, so does ideational
generativity for man. Loss of these respective
complex behaviours means death of the species.
Mortality, bodily death = the second death
Drastic reduction ofmortality
=death ofthe second death
=death squared
=(death)2
(Death)2 leads to dissolution of social organization
=death ofthe establishment
Death of the establishment leads to spiritual death
=loss of capacity to engage in behaviours essential to
species survival
=the first death
Therefore:
(Death)2 =the first death.
Happy is the man who finds wisdom,
and the man who gains understanding.
Wisdom is a tree oflife to those who
lay hold ofher.
All her paths lead to peace.
(Proverbs iii.13, 18 and 17, rearranged)
REFERENCES
Calhoun J B
(1963) In: Physiological Mammalogy. Ed. W Mayer &
R Van Gelder. Academic Press, New York; 1, 1-187
(1967) In: Comparative Psychopathology. Ed. J Zubin.
Grune & Stratton, New York; pp 1-51
(1969) Architectural Association Quarterly 1, No. 3, 24-35
(1971) In: Behavior and Environment - The Use ofSpace by
Animals and Men. Ed. A H Esser. Plenum, New York; pp 329-387
Marsden H M (1972) In: Environment and the Social Sciences:
Perspectives and Applications. Ed. J F Wohwill & D H Carson.
American Psychological Association, Washington, DC; pp 5-14
Marsden H M, Calhoun J B & Ng L K Y
(1971) Crowding and Maladaptation: Behavioral and
Neurochemical Observations. (Paper presented at the
Annual Meeting ofthe American Association for the
Advancement ofSciences, Philadelphia, December 1971
(unpublished)
Wigotsky V W (1970) In: Engineering and the
Urban Crisis: Part 3. Urban Congestion.
Design News, Cahners, Denver, Col.; September 15, pp 48-60

DISCUSSION
The Chairman thought Dr Calhoun had not mentioned
pollution and asked what remains the animals left and
how these affected the situation?
Dr Calhoun said that they (the investigators) were not
very sanitary in their husbandry, if that was the kind
of pollution inferred. The environment was cleaned,
most fices and soiled bedding removed, every six
weeks or two months, but nothing was ever sterilized.
He did not consider this necessary in such a closed
system and the mice had better survival than in most
laboratory colonies. Dead bodies were eventually
removed for examinations, but the major pollution
was the excess of living bodies; this was the essential
factor. The pollution was social in that there were too
many interacting elements, exceeding the social
system's capacity for incorporation ofnew individuals.
Capacities were genetically determined and situation-
ally modified.
The Chairman thought the point had been made very
clearly, but there must be a pollution factor. There
were the remains, frces, urine and dead bodies. Those
must surely be a factor.
Dr Calhoun thought these were minor factors. They
needed to maintain a situation in which there was not
continuous waste accumulation, but beyond that the
environment mirrored certain normal, external
ecological settings.
Dr John F Stokes (London) said he was interested in
Dr Calhoun's diagram illustrating pupping rates,
which showed much greater fertility in the south and
west than in the north and east. If he had understood
the construction of Dr Calhoun's 'universe' correctly,
there were no external indications which could tell the
mice in which direction they faced (though there was
an arrow pointing north on the diagram). He enquired
whether Dr Calhoun thought that other influences
might determine the uneven distribution ofpups.
Dr Calhoun replied that it was his present conviction
that the social system of mice in Universe 25 would
have developed a bilateral symmetry of organization
whether or not some external cues might have in-
fluenced the particular direction that the social axis
assumed. Four other smaller mouse populations had
not been examined for geographical orientation. Other
factors such as air flow could have had some influence,
but he thought the uneven distribution was a chance
phenomenon which once established maintained
itself through social processes.
The Chairman observed that Dr Calhoun had stated
that the dominant males were more active. He asked
how this had been measured.
Dr Calhoun said that animals were individually colour
marked and that specific locations in the environment
were coded. Visual observations of the degree of
movement of individuals and in what place were
correlated with data on social interactions. They had
taken about a million observations on the set of
populations, of which Universe 25 was the largest and
had been followed for the longest period of time. It
had been a long-term study and they were in the
process of structuring their data on magnetic tape
for detailed analysis.
Professor R A Weale (Institute of Ophthalmology,
London) said that the appearance of Dr Calhoun's
mice resulting from the colour coding he used might
affect their behaviour even though they had no colour
vision.
Dr Calhoun replied that this was a frequent question,
that there were preliminary indications of some effect
but the question could not really be answered until
statistical analyses were available. Whether these
effects were visual or olfactory could not be determined
but in any case the mice were capable of recognizing
each other without markings. Movements and body
posture conveyed a great deal of information and he
thought these factors were far more important than
colour.
Professor Mellanby said Dr Calhoun had suggested
that by 1984 man was going to be as crowded as his
mice and that this would have disastrous effects.
Experiments had been going on for a long time with
man. Man was not uniformly distributed. He lived in
some communities just as crowded as Dr Calhoun's
mice. Professor Mellanby had been very familiar with
populations in parts of London forty years ago which
were restricted communities. People seldom moved
out of them. Until the children were taken to camps
for holidays they had seldom been more than a quarter
of a mile from their homes. They were living amidst
extreme crowding and bred very successfully. There-
fore, was it not possible to get an answer to this for
human beings by examining such communities? Did
crowded, enclosed communities behave like the mice?
Or did this occur most obviously in those communities
which had about the lowest population density in
Sweden or the United States?
Dr Calhoun replied that 1984 was not the year in
which ultimate density would be attained, but a date
beyond which the opportunity for decision making
and designing to avoid population catastrophe might
be quickly lost. He stated, in any case, that density
per se was not the major factor, that rate and quality
of social interaction were paramount issues. Basic to
his thesis was that despite the thousandfold increase
in human numbers since the beginning of culture,
some forty to fifty thousand years ago, there had been
no change in effective density. The reason for this,
alluded to by Professor Young, was that man had
discovered a new kind of space, conceptual space,
which enabled man to utilize ideas in order to mine
resources and guide social relations. However, there
was a breaking point for this process, at which time
physical density might overwhelm man's ability to
utilize conceptual space in order to cope with increas-
ing numbers and it was that breaking point which we
might be rapidly approaching. The fact that reproduc-
tion could be affected by density had been dealt with
by Dr Thompson in Indianapolis (Thompson 1969).
An older study for Scotland (Kincaid 1965) had shown
that stillbirths and other parameters were density
87

88 Proc. roy. Soc. Med. Volume 66Januarv 1973
related. However, in terms of conceptual space, it
might be the necessityfor limitations to growth which
might be the more difficult conceptual area for man
to deal with. In that case a further increase in birth
rate might be expected past the breaking point (Galle
et al. 1972).
REFERENCES
Galle 0 R, Gove W R & McPherson J M (1972) Science 176, 23-30
Kincaid J C (1965) British MedicalJournali, 1057-1060
Thompson J F (1969) American Journal ofObstetrics
and Gynecology 105, 1215-1221
The Chairman interrupted Dr Calhoun and said that
he ought to be careful about this. He had been dis-
cussing mice, and the Chairman agreed with Professor
Mellanby that there were some very strong contra-
indications. Hong Kong, for example, was a most
marvellous population of people living under much
higher densities than in east London. He thought the
inhabitants to be impressively happy as far as one
could see.
Dr Calhoun thought this to be a major trap. The
essential core of man was to remain under tension.
What happened in the mice was this: He called the
males the 'beautiful ones'. Those at the end had a
kind ofautistic life. They could function under normal
routine conditions but beyond this the major powers
of the species were lost. He did not know what
happened in Hong Kong. He had been in Calcutta
and was frightened by it. His interpretation of what
was happening there might be happening in Amster-
dam and other places now. He thought mankind was
on a knife-edge which could shift in a couple of
directions. One behavioural shift on the human side
could be comparable to 'beautiful one' mice: indivi-
duals capable of the routine of life, but with loss of
creativity and an inability to live under challenge.
Mr Selwyn Taylor (London) asked Dr Calhoun if he
had made any measurements of the endocrine para-
meters in his mice in the declining part of the popula-
tion curve?
Dr Calhoun replied that Dr Julius Axelrod and Dr
Larry Ng and their associates had measured catechol-
amine synthesizing enzymes in brain and adrenal
glands in mice selected (by Dr Calhoun, Dr Marsden
and their associates) to represent specific behavioural
states existing during the declining crowded popula-
tions. It (neuroendocrinology) was not his field but,
in general, the biochemical picture suggested a higher
degree of physiological stress in 'socially withdrawn'
mice as opposed to aggressive territorial mice. An
intriguing finding related to a third group of mice, the
'beautiful ones', mice in excellent physical condition
but mice which did not engage in social interaction.
Their catecholamine metabolism was comparable to
the territorial animals. They were physically healthy
but never attempted to cope with the social situation.
Rather than socially withdrawing from the system, the
implication was that they never attempted to enter it.
All of these various types of mice evolved in the
crowded environment but because of differing roles,
or rather lack of social roles or rejection from
attempted roles, their behavioural and biochemical
profiles were quite different.
The Chairman asked about the steroids.
Dr Calhoun said that a more comprehensive picture of
the physiology was not obtained. Such a co-ordinated
effort had to be planned from the beginning. The real
dilemma was the removal of sufficient numbers of
animals with known histories at critical points in
population growth. Removal of large numbers of
animals at any point in a population's history pre-
sented the risk of disturbing the later history. The only
effective approach would be to run a large number of
populations and terminate them at critical periods.
The labour problem was tremendous. This was not
normal science, a balanced experiment. It was
observation and reconstruction of a process; it was
historical.
Dr James P Henry (University ofSouthern California)
said that for the past ten years his group had been
following up on Dr Calhoun's approach of working
with socially interacting, freely breeding groups of
rodents. They had used smaller colonies of 17 to 50
CBA mice and had studied normal and socially
deprived animals using intercommunicating systems of
standard boxes. Role behaviour was monitored by a
magnetic tagging method (Ely et al. 1972). In the
socially deprived groups persistent fighting and social
disorder had been associated with a slowly developing
elevation of the adrenal medullary catecholamine-
synthesizing enzymes, tyrosine hydroxylase and
phenylethanolamine N-methyltransferase (Henry,
Stephens et al. 1971). There had been a sustained
systolic arterial hypertension. After several months
this had become fixed, despite removal of the stimulus
(Henry et al. 1967). In animals which had experienced
six months or more ofthis social stimulation there had
been a gross increase in the incidence and severity of
aortic and intramural coronary vascular arterio-
sclerosis, of glomerular mesangial changes, and of
myocardial fibrosis and chronic interstitial nephritis
(Henry, Ely et al. 1971).
REFERENCES
Ely D L, Henry J A, Henry J P & Rader R D
(1972)Physiology & Behavior 9 (in press)
Henry J P, Ely D L, Stephens P M, Ratcliffe H L, Santisteban G A
& Shapiro A P (1971) Atherosclerosis 14, 203-218
Henry J P, Meehan J P & Stephens P M
(1967) Psychosomatic Medicine 29,408-432
Henry J P, Stephens P M, Axelrod J & Mueller R A
(1971) Psychosomatic Medicine 33, 227-237
Dr John Burkinshaw (London) wondered whether
throughout his experiment Dr Calhoun had observed
anything among the mice which could be interpreted
as a mutation.
Dr Calhoun felt that there probably was some muta-
tion. Mice which continually circled, about a dozen,
had been noted, but these might have been 'vestibular'
mice and a result of an infection, not mutation. Even
if mutation rates were known, the first generation
would have been very much like the last. So the real
conclusion was that tremendous behavioural differen-
tiation could occur as a result of social environmental
influences even given a high degree of genetic
homozygosity.

The Explosive Growth and Demise of a Mouse Population

More Related Content

What's hot (20)

Similar to The Explosive Growth and Demise of a Mouse Population (20)

More from Zbut.Eu (20)

Recently uploaded (20)

The Explosive Growth and Demise of a Mouse Population