Human Population Numbers as a Function of Food Supply

Abstract

Human population growth has typically been seen as the primary causative factor of other ecologically destructive phenomena. Current human disease epidemics are explored as a function of population size. That human population growth is itself a phenomenon with clearly identifiable ecological/biological causes has been overlooked. Here, human population growth is discussed as being subject to the same dynamic processes as the population growth of other species. Contrary to the widely held belief that food production must be increased to feed the growing population, experimental and correlational data indicate that human population growth varies as a function of food availability. By increasing food production for humans, at the expense of other species, the biologically determined effect has been, and continues to be, an increase in the human population. Understanding the relationship between food increases and population increases is proposed as a necessary first step in addressing this global problem. Resistance to this perspective is briefly discussed in terms of cultural bias in science.

Full text

HUMAN POPULATION NUMBERS AS A FUNCTION
OF FOOD SUPPLY
RUSSELL HOPFENBERG1,∗and DAVID PIMENTEL2
1Duke University, Durham, NC, USA; 2Cornell University, Ithaca, NY, USA
(∗author for correspondence, 105 Autumn Drive, Chapel Hill, NC, USA 27516-7744;
e-mail: RussH100@aol.com; tel.: (919) 431 0085)
(Received 11 January 2000; accepted 6 March 2001)
Abstract. Human population growth has typically been seen as the primary causative factor of other ecologi-
cally destructive phenomena. Current human disease epidemics are explored as a function of population size.
That human population growth is itself a phenomenon with clearly identifiable ecological/biological causes
has been overlooked. Here, human population growth is discussed as being subject to the same dynamic
processes as the population growth of other species. Contrary to the widely held belief that food production
must be increased to feed the growing population, experimental and correlational data indicate that human
population growth varies as a function of food availability. By increasing food production for humans, at
the expense of other species, the biologically determined effect has been, and continues to be, an increase
in the human population. Understanding the relationship between food increases and population increases is
proposed as a necessary first step in addressing this global problem. Resistance to this perspective is briefly
discussed in terms of cultural bias in science.
Key words: disease(s), food, food availability, food production, human, population, population growth.
1. Introduction
Of all environmental problems, rapid human population growth is arguably the most
detrimental. In fact, escalating human population is fueling the acceleration of all
environmental problems (Brown and Nielsen, 2000; Plant et al., 2000; Jayne, 1999;
Lelieveld et al., 1999; Carpenter and Watson, 1994; Bartiaux and van Ypersele,
1993; Alper, 1991; Brinckman, 1985). The increase in the number of humans is
responsible for amounts of pollutants dumped into land, water, and atmosphere.
The consumption of land resources has also increased, and at an accelerating rate.
Given the fact that the world population is growing (Marchetti et al., 1996; Pimentel
and Pimentel, 1997), the population size is also seen as the major determinant of the
amount of resources used. The World Health Organization (WHO, 1996a) reports
that more than three billion people are now malnourished – the largest number and
proportion ever. In other words, in many places the number of humans exceeds
the carrying capacity of the area in which they live. With the world population
surpassing six billion, the issue of population growth warrants the most serious
attention.
Given the numerous effects of increased population on the planet, human pop-
ulation growth is seen as the main cause of other biologically and ecologically
Environment, Development and Sustainability 3: 1–15, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.

2r. hopfenberg and d. pimentel
destructive phenomena. In this context, these destructive phenomena are seen as
the dependent variables on one side of an ecological equation and population size
is seen as the independent variable on the other.
Conceptualizing human population growth as an independent variable has led to
an unforeseen consequence. That is, human population has been seen as independent
of other identifiable ecological, biological, and behavioral variables. Some have
proposed that, while natural resources, ecological concerns, and other biological
and behavioral variables can limit human population growth, these same variables,
when increased, do not serve to escalate population growth (Marchetti et al., 1996).
Thus, the causes of human population growth have been left inadequately addressed.
Our position is that population growth, the prime environmental problem affecting
all ecological, biological, and non-living systems, is a function of increasing food
production (Quinn, 1992, 1996, 1998a; Pimentel, 1966, 1996).
2. The current perspective
It is the current perspective in both the scientific and lay communities that food
production must be increased in order to support a growing human population
(Postel, 2001; Bongaarts, 1994; Waggoner, 1994; Brundtland, 1993; Baron, 1992;
Anifowoshe, 1990; Brown, 1989; Robson, 1981). For example, Young (1999) noted
that current UN population projections predict that the population of developing
countries will rise to about eight billion by 2025 and nine billion by 2050. He then
asserted, “It is widely recognized that massive agricultural development will be
needed to feed this added population.”
Some contend that fertility is under cultural and economic control (Marchetti
et al., 1996) and that science and technology will solve all future food prob-
lems (Ausubel, 1996). For example, the ADM Corporation advertises that they
are increasing food production to feed a growing world population. Crop yields in
the US and other countries were significantly increased from 1950 to 1980 (USDA,
1998; Pimentel and Pimentel, 1996). Ausubel (1996) also reported that US wheat
yields tripled from 1940 and corn yields have quintupled. He further indicated that
increased food demand is due to growth in world population. However, as Farb
(1978, p. 121) has pointed out, “intensification of production to feed an increased
population leads to a still greater increase in population.” That is to say that as
more food has been made available ostensibly to alleviate food shortages caused
by the increased number of people, the biologically determined response has been
an increase in the population.
P. Waggoner (personal communication, April 1, 1998) stated that “Because peo-
ple stabilize and even shrink their numbers in wealthy, well-fed countries and mul-
tiply in poor, hungry African ones, food supply seems not to determine human
population.” Abernethy’s (1995) investigations and data contradict these opinions.
Additional data from the US also contradicts Waggoner’s point about where pop-
ulation growth is occurring. The US population doubled from 1935 to 1995 and is

human population numbers as a function of food supply 3
now about 270 million. The US population is projected to double again in about 75
years to 540 million, based on the current rate of the population increase in the US
(USBC, 1998). These data and projections include immigration numbers. In fact,
Bouvier and Grant (1994) have predicted that immigrants and their decedents will
comprise approximately 90% of all US population growth between 1993 and 2050.
Although these projections might be seen as more reflective of the growth rate in
other countries, it is important to remember that the non-native population of the US
has grown from zero to over 270 million in only 510 years. In other words, almost
all of the prodigious population growth on this continent is the result of increases
in the number of immigrants and their descendants. Viewed in this way it becomes
apparent that focusing on the question of where population growth is taking place
may be a distraction from addressing the question of why it is taking place on a
global level.
The prevailing lay and scientific attitudes beg the Malthusian question “how will
the US continue to feed its population and still maintain its food exports to needy
nations?” In other words, “how are we going to feed all these people?” This indicates
a denial of the certainty that increasing the availability of food will further increase
the population, thereby increasing the number of starving and malnourished people.
Thus, it does not address the Quinnian question “how are we going to stop producing
all these people (Quinn, 1997)?” since it is through exports from food-rich to food-
poor areas (Allaby, 1984; Pimentel et al., 1999) that the population growth in these
food-poor areas is further fueled.
Another problem that appears to cloud the picture is that population growth seems
to be slow and gradual. Adding one million to the world population every four days
or adding three million to the US population every year is scarcely noticeable. With
the passage of years, the world population doubled and the US population also
doubled.
3. Animal data
Many field studies have demonstrated that all animals tend to increase and convert
as much of their environmental resources as possible into themselves and their
progeny. Darwin (1859) in his chapter ‘The Struggle For Existence’ pointed out
that food is a critical factor that limited some animal populations. He also noted the
“numerous recorded cases of the astonishingly rapid increase of various animals
in a state of nature, when circumstances have been favorable to them during two
or three following seasons.” Elton (1927) was the first to explicitly state that when
animals start struggling for existence, they spend a large part of their lives eating
and seeking food. He added that the prime driving force for all animals is finding
the right kind of food and finding enough food. Elton (1927, p. 56) in fact pointed
out that “the whole structure and activities of the community are dependent upon
questions of food-supply.”

4r. hopfenberg and d. pimentel
The finding that the population size of animal species is a function of food avail-
ability has been empirically demonstrated. Food energy is partitioned into four
compartments viz.: maintenance, growth, stored energy, and reproduction. Scott
and Fore (1995) investigated the effects of food availability on reproduction in the
marbled salamander. Subjects were assigned to one of three groups. At the end of
the experiment, 60% of the high-food females were reproductive. In the medium-
and low-food groups, these numbers were 42% and 12% respectively. These results
demonstrate that food availability influences the population dynamics of a species.
Similarly, Komdeur (1996) demonstrated that the Seychelles warbler prolonged
their reproductive season, including increases to year-round breeding, when their
natural condition changed to one with high food availability. Conversely, in female
musk shrews (whose sexual receptivity is not restricted to the preovulatory period),
48 h of food restriction led to reduced mating behavior compared with ad-lib con-
trols. Thus, small reductions in food availability can inhibit female sexual behavior
(Gill and Rissman, 1997). In the Calanus finmarchicus, egg production is sup-
pressed when the nutrient pool decreases below a minimal critical value. There-
after, no eggs are laid. When food is reintroduced, somatic growth resumes until
structural body weight is restored, then oogenesis is fueled (Carlotti and Hirche,
1997). Also, Iwamoto (1978) has shown that monkey troop size increases rapidly
after artificial provisioning, but the level of consumption efficiency of the troop is
always maintained lower than the critical point in both the artificial and natural
habitat. Starvation within the troop simply does not occur if the rate of food avail-
ability is held relatively constant. Under natural conditions, as the feeder population
increases, the food population decreases. This leads to a decrease in the feeder pop-
ulation which is then followed by an increase in the food population. This increase
in food availability again produces an increase in the feeder population. In quater-
nary consumer species, the so-called ‘top of the food chain’, this occurs primarily
through fluctuations in birth rates.
Again, the data overwhelmingly establishes that increasing the amount of food
available to the population of any species leads to an increase in the population of
that species and a decrease in the amount of food leads to a decrease in the size
of the affected population (Caceres et al., 1994; McKillup and McKillup, 1994;
Angerbjorn et al., 1991; Wayne et al., 1991; Bomford, 1987).
Some animals, such as rabbits, have evolved the adaptation of increasing their
numbers rapidly as predation and/or disease organisms often limit their numbers
(Elton, 1927; Pimentel, 1988). Some species self-regulate their number to their food
resources by maintaining home ranges. Chitty (1995) reported that excess young
voles, for example, are forced to leave the home range of their parents. While
traveling to find new homes for themselves the young are heavily preyed on or
die of starvation and disease. Possibly more germane is the evidence that a sudden
improvement of diet in sheep cause an increased ovulation rate (Schinkel, 1963) and
that fasting in mice for relatively short periods of time prior to mating resulted in
depression of male libido and reduced conception in females (Christian et al., 1965).

human population numbers as a function of food supply 5
The evidence clearly demonstrates that, although species have evolved different
strategies for adjusting to food supply limitations, food availability influences and
determines the population size of all species.
4. Human correlational data
The populations of human cultures described as hunter-gatherers were limited to the
food resources available (Lee, 1969; Lee and DeVore, 1976; Pimentel and Pimentel,
1996). Where these cultures still exist untouched, this continues to hold true. After
one culture of humans started a program of agricultural expansion about 10 000
years ago (Quinn, 1992) they seem to have generally escaped the controls and
limits of natural resources. However, this escape is proving illusory. Recent data
concerning the increasing malnutrition and diseases in the human population world-
wide indicates that human numbers will be limited in other ways (Pimentel et al.,
1999). If increases continue, the population will ultimately be controlled through
mechanisms such as malnutrition and disease, i.e., by means of accelerated death
rates.
Marchetti et al. (1996) have extrapolated human population data back to 10 000
BCE and show a geometrically increasing population. Although humans have been
on the planet for over two million years, it is interesting that they chose to extrapolate
back to 10 000 BCE as this is the usually agreed upon beginning of the ‘agricultural
revolution’. The agricultural revolution produced human food surpluses, through a
program of expansion and elimination of competing cultures and species (Quinn,
1992; Zinn, 1995). The resultant food surplus is both necessary and sufficient to
explain the meteoric rise in the human population in only 500 generations. Based
on the experimental evidence, the correlational data and the seeming coincidence
of agricultural expansion and the prodigious human population increases, there is
overwhelming evidence that food surplus explains, i.e., is causally related to, human
population increases. Pimentel and Pimentel (1996) also noted that growth in human
population numbers began to escalate about 10 000 years ago, when agriculture was
first initiated. Farb (1978, p. 129) stated “The population explosion, the shortage
of resources, the pollution of the environment, exploitation of one human group by
another, famine and war – all have their roots in that great adaptive change from
foraging to production.” Given the current environmental crisis, after only 10 000
years of agricultural expansion, it is curious that he called this change adaptive.
Other more recent data are available. For example, for the period of 1989–91, the
world crop production index rose 25% over the 1979–81 level. The increase over the
period of 1994–96 was 41.3% greater than the 1979–81 level (World Development
Indicators, 1998). Similarly, the food production index for the same time periods
rose 25.6% and 45.6%. The livestock production index rose 24.1% and 46.6%,
again for the same time periods. World cereal yield in kilograms per hectare rose
from 2,230 to 2,561 over the periods 1979–81 to 1994–96. Thus food production

6r. hopfenberg and d. pimentel
has increased sufficiently, i.e., produced sufficient food surpluses, to keep the world
population growing catastrophically (Quinn, 1998b) even though food production
increases have slowed since 1983. For instance, per capita grain production started
declining after 1983 (Pimentel et al., 1999). Note, grains make up 80% to 90% of
world food.
It is clear that world human food availability continues to grow, but at reduced
rates (Allaby, 1984; Pimentel et al., 1999). Livestock currently consume 130 million
tons of grain in the US, enough to feed about 400 million people (Pimentel, 1996;
Pimentel et al., 1995). Certainly there would be even more human food available if
dependence on livestock was decreased. However, because human population is a
function of food availability, the resulting increase in available human food would
induce a commensurate rise in population. This population increase would ulti-
mately exacerbate the starvation and malnutrition predicament. Since it is known
that human population expansion is correlated with a decrease in available land,
water, energy, and biological resources, there is a suggested cause and effect rela-
tionship between these decreases and human population growth.
Given that the increases in food availability cause increases in population growth,
this accounts for the reduction in global biodiversity. Humans are now utilizing
about 50% of the world’s biomass for their own use (Pimentel and Pimentel, 1996).
Clearly, as the amount of human food and, contingently, the number of humans esca-
lates, the biomass available for other species goes down and biodiversity declines.
5. Population increases and human diseases
Many of the variables that affect population size are density-dependent factors
(Emmel, 1973; Gotelli, 1998). As the density of the human population increases, the
amount of resources available to individuals decreases. Beyond a certain population
density, health declines and mortality rates increase.
At first glance, human health seems unrelated to natural resources; but upon closer
consideration, it becomes apparent that both the quality and quantity of natural
resources (e.g., food and water) play a central role in human health. Increases in
diseases associated with diminishing quality of water, air, and soil resources provide
evidence of a declining standard of living. Profound differences exist in the causes
of death between developed and developing regions of the world. Communicable,
maternal, and/or prenatal diseases account for 40% of the deaths in developing
regions but only 5% in developed regions (WHO, 1996b). While there is a complex
set of factors responsible, large population increases followed by inadequate food,
and contaminated water and soil are the major contributors to diseases and other
health problems, especially in developing countries (Pimentel et al., 1998).
As populations increase in size, risks to health grow as well, and this occurs
especially rapidly in areas where sanitation is inadequate. Human deaths due to
infectious diseases increased more than 60% from 1982 to 1992 (WHO, 1992,
1995).

human population numbers as a function of food supply 7
Overcrowded urban environments, especially those without proper sanitation, are
of great public health concern because they have the potential to be the source of
disease epidemics (Iseki, 1994; Holden, 1995) and increased pollution (Brown and
Nielsen, 2000; Plant et al., 2000; Jayne, 1999; Lelieveld et al., 1999; Carpenter and
Watson, 1994; Bartiaux and van Ypersele, 1993; Alper, 1991; Brinckman, 1985).
For example, dengue – spread by the mosquito Aedes aegypti which breeds in water
holding containers including tin cans, old tires, and other containers – is spreading
rapidly in crowded tropical cities (Lederberg et al., 1992; Gubler and Clark, 1996).
Currently there are 30 to 60 million infections of dengue per year, with a dramatic
increase since 1980 (Monath, 1994). Approximately 65% of the world’s infectious
diseases are spread from person to person (WHO, 1996a). In addition to the increase
in infectious diseases that now cause 35% of human deaths (Ramalingaswami,
1996), it is estimated that another 40% of human deaths each year can be attributed to
various environmental factors, especially organic and chemical pollutants (Pimentel
et al., 1998).
Worldwide waterborne infections account for 80% of all infectious diseases and
90% of infectious diseases in developing countries (Epstein et al., 1994). Lack of
sanitary conditions contributes to about two billion human infections of diarrhoea
with about four million deaths per year, mostly among infants and young children
(WHO, 1992).
Developing countries discharge approximately 95% of their untreated urban
sewage directly into surface waters (WHO/UNEP, 1993). Of India’s 3,119 towns
and cities, just 209 have partial treatment facilities and only eight have full wastew-
ater treatment facilities (WHO, 1992). Downstream, the untreated water is used for
drinking, bathing, and washing.
In the United States, nearly 50% of the lake water is polluted by erosion runoff
containing nitrates, phosphates, and other chemicals (Gleick, 1993). Non-point
sources of US pollution, especially agricultural runoff (e.g., animal wastes and
pesticides) also contribute to disease problems.
Schistosomiasis, long associated with water and unsanitary conditions, is expand-
ing worldwide and currently causes an estimated one million deaths annually
(Pimentel et al., 1998). This expansion follows an increase in habitats for the snail
intermediate-host population made by various human activities, such as the con-
struction of dams and irrigation channels (Shiklomanov, 1993). For example, con-
struction of the Aswan High Dam in Egypt led to an explosion in the incidence
of Schistosoma mansoni from 5% in 1968 to 77% in 1993 (Shiklomanov, 1993).
Infections of S. heamatobium ranged between 2% and 11% before dam construction
in 1968, but increased to between 44% and 77% in 1990 (Akhtar and Verhasselt,
1990).
Malaria, a mosquito-borne disease, infects more than 500 million humans each
year, killing approximately 2.7 million people (Marshall, 1997; Travis, 1997). Envi-
ronmental changes, including more polluted water and deforestation, have fostered
the high incidence and increase in malaria.

8r. hopfenberg and d. pimentel
In addition, air pollutants adversely affect the health of about four to five billion
people worldwide each year (World Bank, 1992; Leslie and Haraprasad, 1993;
WHO/UNEP, 1993). Increasingly, air pollution is associated with the expanding
world population; the burning of fossil fuels; increased release of industrial chemical
emissions; and more automobiles.
Globally, especially in developing nations where people cook with fuelwood and
coal over open fires, about four billion humans suffer from exposure to smoke each
year (WHO, 1992; World Bank, 1992; Leslie and Haraprasad, 1993; WHO/UNEP,
1993). This smoke contains large quantities of particulate matter (Leslie and Hara-
prasad, 1993) and more than 200 chemicals, including several carcinogens (Godish,
1991) and represents pollution levels considerably above those acceptable by the
World Health Organization (WHO, 1992; World Bank, 1992; Leslie and Hara-
prasad, 1993; WHO/UNEP, 1993). Of the estimated 2.7 million deaths per year
related to air pollution, 2.2 million are caused by pollutants from wood and other
fuels burned indoors for cooking and heating (UNDP, 1999).
One of the most severe human diseases related to shortages of natural resources
is malnutrition. This malnutrition relates to shortages of calories, protein, vitamins
(e.g., vitamin A), iron, iodine, and others. Today, more than three billion people (one-
half of the world population) suffer from malnutrition (WHO, 1996a), the largest
number and proportion ever in history. In other words, as the global population has
grown, the number and proportion of malnourished individuals has grown. Thus it
can be asserted that the increase in the number and proportion of people suffering
from malnutrition is a function of population size.
Poverty and lack of sanitation can be as severe in certain urban sectors as they
are in rural areas; several studies point to inequalities even within different parts
of individual cities (Pimentel et al., 1998). Urban environments, especially those
without proper sanitation, are becoming a cause for concern due to their high poten-
tial for the spread of disease due to overcrowding (Holden, 1995). The high density
of people in urban environments provides no protection from pollution caused by
accumulation of city wastes in water, air, and soil, and creates favorable conditions
for the rapid spread of infectious diseases that can easily reach epidemic proportions
(WHO, 1992).
Malnutrition and other diseases are interrelated and, as might be expected, par-
asitic infections and malnutrition coexist where there is poverty, poor sanitation
(Shetty and Shetty, 1993) and high population density (Gotelli, 1998). Malnour-
ished individuals, especially children, are seriously affected by parasitic infections
because these infections can reduce the nutrient availability from the children’s
diet. Intestinal parasites, like hookworms, reduce the uptake of nutrients in infected
humans. They increase the loss of nutrients through diarrhoea and dysentery, impair
nutrient absorption, frequently diminish appetite and food intake, and directly ingest
blood (Shetty and Shetty, 1993). Hookworms, for instance, can remove up to 30 cc
of blood from an infected person each day, leaving the individual weak and suscep-
tible to other diseases (Hotez and Pritchard, 1995). An estimated 5% to 20% of an

human population numbers as a function of food supply 9
individual’s daily food intake is used to offset a parasitic illnesses and stress of the
disease (Pimentel and Pimentel, 1996).
It has been said that the suffering of those who are currently malnourished could
be ameliorated through improved food distribution (Hay, 1981). Kofi Annan (1997),
Secretary-General of the United Nations stated: “The world has enough food. What
it lacks is the political will to ensure that all people have access to this bounty, that
all people enjoy food security.” Also, alternatives to increasing food production
have been suggested. For example, the nutrition of the world population might be
improved temporarily with better distribution of total world food without increasing
production. For instance, it might be possible to feed the current six billion people
a minimal but nutritionally adequate diet, if all food produced in the world was
shared and distributed equally (Cohen, 1995). Yet, there are problems with this
proposal. For example, how many people in developed and developing countries
who have more than their basic needs of food resources would be willing to share
their food and pay for its production and distribution? Whether or not improved
distribution occurs, if food production continues to increase, the world population
is projected to increase to 12 billion in the next 50 years (based on current growth
rates). Severe shortages of land, water, energy, and biological resources will increase
malnutrition and food shortages (Abernethy, 1993). This also points to the reality
that food production will be capped at some point, as the planet’s ability to produce
food is finite.
6. The effects of halting increases in food production
The population growth curve characteristic of most species is sigmoid or s-shaped.
This is as true for paramecia as it is for larger organisms with long life cycles such as
birds, trees, and mammals. Growth starts slowly, accelerates rapidly in exponential
form, and then decelerates as it approaches the asymptote of environmental limits.
For all species limited by density-dependent factors, including humans, this limit
can be determined by food availability. The food may also be called one of the
carrying capacity limits of the environment. Once a population has reached a food
limitation, a relative equilibrium may be reached. This equilibrium involves fluc-
tuations in population size, and these fluctuations follow the periodic fluctuations
of food levels and/or predation and disease outbreaks. Generally, as feeder popu-
lations increase, the food resources decrease. This is followed by a decrease in the
feeder populations which allows food resources to again increase. These long-term
oscillations in population density may occur with many years between peaks and
depressions (Emmel, 1973 p. 86–98; Chitty, 1995).
By increasing agricultural production, humans have continually ‘raised the ceil-
ing’, i.e., the asymptote of food limitation. That is, through agricultural production,
the amount of human food produced is increased. This sets the occasion for a decline
in human food resources which may occur through events such as drought or other
problems. Thus, when the food resources decline, it may occur in a precipitous

10 r. hopfenberg and d. pimentel
fashion. This future crisis may be the direct result of increasing the human popu-
lation beyond the carrying capacity of the environment. In other words, the higher
the ceiling, the more serious the crash. Robson (1981) suggested that famines do
not occur divorced from intensive agricultural production.
Quinn (1996) has called our program of increasing food production in order to
maintain population growth ‘totalitarian agriculture’. In response to the claim that
food production must be increased to feed a growing population, Quinn (1998c)
has responded that
If six billion people can be fed by totalitarian agriculture, then the same six billion can
be fed by sustainable agriculture. The difference between totalitarian agriculture and
sustainable agriculture is not technique or output (since a turnip is a turnip however it’s
produced) but rather program. The program of totalitarian agriculture is to increase food
production in order to outpace population growth that is fueled by the very increases it
produces, and this is what makes it unsustainable.
The notion that as the population approaches the asymptote of food limits, mass
starvation will ensue has been implied, if not stated explicitly. Throughout the
literature on the subject, the position has been “we must increase food production
to feed a growing population” (Postel, 2001; Bongaarts, 1994; Waggoner, 1994;
Brundtland, 1993; Baron, 1992; Anifowoshe, 1990; Brown, 1989; Robson, 1981).
Malthus, in his famous Essay, put forth his ‘principle of population’ which was
his assertion that the population has the capacity to grow faster than the means
of subsistence (Petersen, 1979, p. 47). However, due to biological realities, the
population cannot be sustained beyond the level of food availability. Because of
the Malthusian perspective which is pervasive in our culture, that ‘food production
must be increased to feed a growing population’, that, in fact, is what occurs. The
result is annual food production increases that cause annual population increases,
with seriously increasing malnutrition and added diseases. However, the evidence
indicates that the human population will increase until further food limitations are
reached. Then population growth will be restricted (Pimentel and Pimentel, 1996,
pp. 23, 296).
If food availability for the population is held constant and population increases
continue at 1.4% per year (PRB, 2000), the reduction in per capita food per year is
relatively small on average (Quinn, 1998a). For example, if a population consists of
1,000 humans and food availability for this population is held constant forever, and
allows for 3,000 calories per person per day (holding other vital nutrients constant
relative to calorie count), this is a total calorie count of three million calories per
day. Ifthe number of people increases to 1,014, the number of calories per person
per day is reduced to 2,959. If the same amount of population growth occurs the next
year, the population will grow to 1,028. The calories per person per day will then
be 2,918. Repeated twice more, the calories available per person per day will drop
to 2,879 and then to 2,838. After four years of 1.4% population growth, calories per
person per day is reduced by only 162. After a total of nine years, the reduction in
calories is only 353, to a level of 2,648 calories per person per day. The impingement

human population numbers as a function of food supply 11
of the food and nutrient limitation, although subtle, will eventually serve to curb
human reproduction. This may occur through social mechanisms, choice behavior
or reproductive–biological mechanisms. In other words, halting increases in food
production will halt the increases in population by means of a reduced birth rate.
Thus, there appears to be two available systemic methods of population control.
One is to continue to fuel population growth through increased food production
and allow biological mechanisms such as malnutrition and disease to limit the
population by means of an increased death rate. The other is to cap the increases in
food production and thereby halt the increases in population by means of a reduced
birth rate. Instead of depending on malnutrition and disease to limit human numbers,
a social mechanism in response to a stable food supply, might be for humans to
limit their numbers democratically or consensually or to employ incentives.
7. Cultural bias in science
Cultural bias in science is not new. When Charles Darwin (1859) put forward the
notion that humans came into being by an evolutionary process his theory faced
strong opposition, especially from the clergy. Evolutionary theory has gained accep-
tance but is not acknowledged by many segments of society. Perhaps the same cul-
tural bias that interfered with the acceptance of Galileo’s observations and assertions
supporting Copernican theory (Finocchiaro, 1989), continues to interfere with the
acceptance of Darwin’s proposals (note the Kansas board of Education’s decision
to abolish the requirement for teaching evolution – New York Times, August 12,
1999). The view that humans are above the natural physical and biological laws
continues today.
A similar bias is also present regarding understanding the cause-and-effect rela-
tionship between food production and human population growth. Some, like Julian
Simon (1991) hold that humans are exempt from the natural laws of physics and
biology and that human behavior occurs as a result of metaphysical forces. P. Wag-
goner (personal communication, April 1, 1998) stated that “we ...question whether
something (population growth) so dependent on human wishes can be predicted
physically.” Because of this belief, the use of the scientific method to study human
behavior, especially as it relates to population dynamics, is in its infancy, and still
looked upon with skepticism (Skinner, 1990).
8. Coda
Clearly, human numbers cannot continue to increase indefinitely and defy all
the physical and biological laws. Natural resources are already severely limited,
and there is emerging evidence that natural forces are already starting to control
human population numbers through malnutrition and other diseases, i.e., through an
increased death rate. More than three billion people worldwide are already malnour-
ished. Pollution of water, air, and land has increased, resulting in a rapid increase in

12 r. hopfenberg and d. pimentel
the number of humans suffering from serious, pollution-related diseases (Pimentel
et al., 1998). Again, it is clear that natural forces are at work to increase human
death rates.
Fifty-eight academies of science, including the US National Academy of Sci-
ences, point out that humanity is approaching a crisis with respect to the issues of
natural resources, population, and sustainability (NAS, 1994). If the program of
‘increasing food production in order to feed a growing population’ continues to be
pursued, human numbers will continue to increase beyond the ability of the natural
community to support those numbers. Then disease, including malnutrition, and
other natural controls will limit human numbers. However, population control does
not have to occur this way if it is understood that our program of increasing food
production continues fueling the population explosion.
Some people believe that for humans to limit their numbers would infringe on
their freedom to reproduce. This may be true, but a continued increase in human
numbers will infringe on our freedoms from malnutrition, hunger, disease, poverty,
and pollution, and on our freedom to enjoy nature and a quality environment.
By understanding the relevant scientific laws regarding population dynamics that
human population size is a function of food availability, we have an opportunity to
ensure the well being of future generations. Individuals will then live in an envi-
ronment capable of sustaining human, and other life.
Acknowledgements
We wish to thank Edie Hopfenberg, Steven Salmony, and Jeffrey Wysocki for their
helpful discussion, useful suggestions and thoughtful review of earlier drafts.
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