Population and The
Lecture 2 Outline
• Introduction: Why are we discussing human population in an
Environmental Biology class?
• Population growth
• Human population change over time
– Developed and Less Developed nations
– Population Parameters
• Crude birth/death rate
• Infant mortality rate
• Life expectancy
• Total fertility rate
• Population pyramids
• Demographic Transition
• Perspectives on population
Introduction: Human Population
and the Environment
• Paul Ehrlich‟s published “The Population Bomb” in 1968. This work
was one of the original accusations that any environmental issue is
really just a human overpopulation issue. That is, every
environmental problem is directly related to there being too many
people. Continuing with this argument, the way to help the
environment, then, is to control over population.
• Some of Ehrlich‟s ideas sparked a lot of controversy. Indeed as we
shall read later in the lecture, some of Ehrlich‟s ideas are very
draconian, and he is often heavily criticized.
• But important questions remain:
– Do we have a human population problem?
– If so, is overpopulation at the root of all environmental problems?
– Can the population be controlled?
– What strategies exist to keep population in check, and will these
measures help the environment?
• Before discussing human population, it would
be prudent to review general ecological
• How does a species population changes?
– Birth (add more individuals)
– Death (remove individuals)
– Migration (immigration/emigration)
Basic Population Dynamics
• Assuming no migration
– If Births > Deaths, the population
– If Births < Deaths, the population
• For most natural populations,
whether it be humming birds, oak
trees, slime molds, or whatever,
there will be good years when http://www.nature.ca/NOTEBOOKS/images/ruby.gif
populations expand and bad years
when populations decline. Over Higher population
the course of many years,
population changes oscillate around Time
a dynamic equilibrium
When populations increase, they
often do so exponentially
Generation Formula Population
• First, though, lets look at
linear growth 1 2+2 4
• Constant rate of growth
2 4+2 6
whereby two new
individuals are added 3 6+2 8
4 8+2 10
5 10+2 12
When populations increase, they
often do so exponentially
Generation Formula Population
• Exponential growth,
whereby the population 1 2*2 4
doubles each generation
• Compare 5 th generations 2 2*4 8
– Linear = 12 3 2*8 16
– Exponential = 64
4 2*16 32
5 2*32 64
Which would you rather have over 10 week period:
1) One cent, doubles every day
2) One dollar + one additional dollar every day?
Exponential Population Growth
• Standard exponential
R = intrinsic growth curve
growth curve: - based on individual
species growth potential
Exponential Curve (continued)
• Growth is very slow at first, but as the population
increases over time the growth rate becomes enormous
• Question: mathematically, where does this curve go to?
• Is this possible? Of course not. Usually there is some restriction
on population growth, whether it be reduced resources, diseases,
etc. In the real world, populations level off around a “carrying
• Carrying Capacity: “the maximum number of individuals
that the environment can support” (Barbour et al.,
1999), Terrestrial Plant Ecology, pg. 66.
– Usually set by the amount of available resources
• The carrying capacity has a “dampening” function that
limits a population once numbers grow to a certain value.
• As N approaches K, growth declines to zero (K-N)
K = carrying capacity
dN rN ( K N )
• In many real world populations, the number of
individuals vary around the carrying capacity (K) in a
dynamic equilibrium. Sometimes populations crash
when they reach or exceed K (they may exhaust all
available resources or diseases may spread rampantly
with high densities). This is called a population crash;
after a crash population builds slowly again.
So what does all this have to do
with Environmental Biology?
• In the following slides we will be
examining human population and relating
human population to environmental
• Human populations may be constrained
by forces similar to those previously
• Springboard: human population growth.
History of Human Populations
• Prior to ca. 10,000 years ago (kya),
human population growth was very Then about 10 – 8 kya,
slow (similar to the hummingbird
example given earlier). human population growth
Note: the last
100 years have
in human populations
(Chiras, 2001. Environmental Science:
Creating a sustainable future, 6th Edition,
Jones and Bartlett, Sudbury, MD, pg 150.
Early Human Population
• Mostly hunter/gather populations existed
before 10 KYA. These populations were
very small and had very little population
– Death rates and birth rates were both very
high. Catastrophic population crashes were
• At about 10 kya – 8 kya, the population
growth rate increased, why?
• Technically, the “Neolithic
Revolution”, term coined by
– Transition from
hunter/gather to agrarian
– Occurred through the
development of cultivation
of animals and plants
– Occurred in many
different regions of the
• Asia, Africa, North
Why would the Agricultural
Revolution result in greater rate of
• Could be from the improved living conditions and more
abundant food supply. These events would lower the
death rate (traditional view)
• In contrast, it could be that living in closer proximity to
one another actually increased the death rate from the
spread of infectious diseases and through poor
sanitation. The increase in population, then, would be
related to an increase in the fertility rate (average # of
offspring born to a female over the course of her
reproductive lifetime), which may be related to the
abundance of food (archeological view).
• Nonetheless, human populations started to climb
Ag. Revolution to ca. 1800
• This time period is characterized by slow growth. You
textbook mentions “population increased slowly and
variably, with periodic setbacks” (pg 124).
• The population was doubling about every 1200 years
(Chiras, 2001. Environmental Science:
Creating a sustainable future, 6th Edition,
Jones and Bartlett, Sudbury, MD, pg 150.
Human Population 1750 - 1830
• Estimates for human population at 1750 are around 800 million
• World population reached 1 billion for the first time in 1830. What
happened around the mid Eighteen century to explain dramatic rise
– Industrial Revolution
• The Industrial Revolution was another technological advancement
that had an effect on human population. Why? Some possible
– Decrease in the death rate
– Increased birth rate
• Economists suggest that with the Industrial Revolution came a greater
need for labor. This demand for labor may have contributed to the
increase in population – the increase was market-driven.
• The World‟s population reached 2 billion in 1930, only 100 years
since 1830. See the following graph (from textbook).
Human Population: 1000 AD –
present (Figure 5-1)
Note the rapid increase K = 10 billion?
in the growth rate. It is
taking less time to
add an additional
1 billion persons.
Human Population Values
Year (T) Human Population # yrs to add an additional
1 AD - 1750 800,000
1830 1 billion
1930 2 billion 100 years
1960 3 billion 30 years
1975 4 billion 15 years
Note the growth rate
1987 5 billion 12 years is slowing down
1999 6 billion 12 years
(2050) 8.9 billion
Human Population: overall trend
• Most of the World‟s population growth has occurred in the last 100 years or so.
From 1930 – 1999, for example, population went from 2 billion to 6 billion. This is
unprecedented in human history.
• The dramatic rise in population is a result of several factors
– Better healthcare and medicine
– Better nutrition and sanitation practices
– Increase in food production (see the “Green Revolution, pg 236 – 238)
– In short, technological advances in just about every field has contributed
• In recent years, though, population growth has slowed. The time to add 1 billion
people is decreasing, but the amount of the decrease is becoming less and less. For
example, the human population went from 2 billion to 3 billion in 30 years (1930-
1960). Population went from 3 billion to 4 billion in 15 years (1960-1975).
Population increased from 4 billion to 5 billion in 12 years (1975 – 1987).
Population increased from 5 billion to 6 billion in 12 years; this is the same rate of
increase as the 4 – 5 billion. The rate of increase is slowing.
• Even though the rate of population increase is lessening, be cognizant that the
overall number of people is still expanding.
World Population growth, rate
and absolute growth (Fig 5-2)
• Human population numbers are increasing, but the
growth rate is declining. Are we reaching carrying
capacity? See the “dampening” factor in the equation
on slide 10.
Human Population Growth and
• The increase in human populations is an environmental concern for several
reasons: Below are just a few:
– 1) more waste
– 2) use more resources
– 3) increased land development for both agriculture and habitation
– 4) more energy demands
– 5) greater pressure on wildlife and greater pressure on marine life
• It is suggested, then, that human population growth is the biggest threat to
• Human population growth may possibly be the greatest threat to humans
as well. Keep in mind the concept of the carrying capacity. Once
populations numbers = k, the growth rate drops. Sometimes if the
population increases too fast and the numbers exceed K, the amount of
available resources plummet and the population crashes. Again, what is the
human carrying capacity? How many people will the World support? Have
we already exceeded K, and if so, are we susceptible to a major population
crash? We will address some of these issues in just a bit.
• Human population growth is not the same globally. One of the greatest factors
influencing population is the economic status of a nation or region.
• Your textbook defines three types of countries based on their economic status.
NOTE: the following discussion is based on economic status and NOT cultural
– High-income, industrialized countries (e.g. US, Canada, Japan, UK, France).
– Middle-income/ moderately developed (e.g. Russia, eastern Europe, Mexico, Costa Rica)
– Low-income, developing countries (e.g. Nicaragua, Angola, Ethiopia).
– Note: the terms “Developed” and “Developing” are used to represent the economic
status of nations. Developed nations include the US, western Europe, Scandinavia, UK,
Australia, New Zealand, Canada, Japan, Taiwan, and several “Arab states”. “Developing”
nations are everyone else.
• See Figure 5-4 to see the distribution of these three economic groups. (The file size
of this image was too large to include in the PowerPoint).
• There are many disparities between the high-income (HI) and low-income (LI).
– HI make up 16% of the World‟s population but control about 81% of the wealth (GNP; pg.
– LI make up 41% of the World‟s population but control only 3.4% of the wealth (GNP; pg
Comparison of Populations
Between Developed and
• In order to discuss global variations in human population, we must first define certain population
parameters (see Table 5-1, pg 126):
– Growth Rate = the rate of growth of a population as a percentage. Multiplied by the existing population,
this rate gives the net yearly increase.
– Total Fertility Rate = the average number of children each woman has over her lifetime. This is the most
widely used measure of fertility, and is seen as being superior to the crude birth rate. One advantage is
that the TFR focuses on women that are fertile, i.e.. the members of the population that are actually
– Replacement-level Fertility = a fertility rate that will replace just the mom and dad, theoretically 2.0. Mom
has 2 kids, so when mom and dad both die 2 additional people (the offspring) will take their place; the
population is stable. Less than 2.0 the population declines; greater than 2.0 the population increases
– Infant Mortality = number of infant deaths per 1000 live births. Infant mortality is a more reflective death
rate statistic than crude death rate (below) because it focuses on a more sensitive age group and because
it doesn‟t include persons that would die from old age.
– Crude Birth Rate = number of births per thousand people. Not an accurate statistic because the
“thousand people” include both males and females. As far as I am aware, males can‟t have kids. The CBR
is somewhat skewed by including in the calculations members of the population that can‟t reproduce.
– Crude Death Rate = number of deaths per thousand. Not a very reflective statistic because it
incorporates the people who would be dying of old age, even after a long and healthy life.
– Doubling Time = The time it takes for a population increasing at a give growth rate to double in size. In
the human population history, the doubling time from 1 billion to 2 billion was 100 years.
• The next slide compares some of these population parameters between developed and
developing nations. This information is derived from Table 5 - 3
Table 5-3: Population
Data for Selected
• Note the relationship
between development status
and total fertility rate.
• Note the US is the only
developed country that has a
TFR capable of increasing
(maintaining) the population.
Actually, some estimates for
US TFR are closer to 3
Population increase in Developed
and Developing Countries (Figure
• The higher TFR means that the developing countries are
experiencing the greater population increase.
Ecological Footprint (Figure 5-7)
• Ehrlich and Holdren propose that the environmental impact is related to human population and the
varying degrees of pressure different people put on the environment (see pg 130).
• Their premise is that the more affluent countries, even though they are smaller in population, have
more of an affect on the environment because they use substantially more resources. Thus, in this case,
human population differences between developed and developing nations may not be the sole reason
for environmental degradation. As mentioned in the textbook “it is hypocritical to criticize developing
countries for continuing to grow their populations. Those who live in wealthy, but population-stable,
developed countries are equally guilty of environmental misuse” (pg 130).
• The US for example has 5% of the population but is currently responsible for 24% of the total global
emissions of CO2.
• The US, then, has a lager “Ecological footprint” than other developing countries.
Personally I question the source of this
graph especially regarding China and
India’s contribution. I agree with the
overall concept, but disagree with the
details. This is my own personal opinion.
(new section) Population Profiles
• In predicting future population trends, it is
important to look at population growth by age
group. For example, looking at the age
structure of a population, whether the bulk of
the population is older or younger, can provide
insight into future population numbers. This
relationship is displayed in “population profiles”,
which is a “bar graph showing the number or
proportion of people at each age for a given
population”, pg 138).
Population Profiles: US Fig 5-12)
2050 Age group (cohort) is on
the y-axis and population
is on the x-axis. Males and
females are separated. Note
with a TFR > 2, the SU population
is expected to increase.
Population Profile: Developed
Country (Fig. 5- 14)
• Italy is a developed country
with a TFR = 1.2. Note how
the population is expected to
• The “characteristic shape of a
developed country profile is
usually top-heavy (more
people in the older
generations, TFR < 2) or
uniform (all generations have
about the same numbers, TFR
Population Profile: Developing
Countries (fig 5-16)
• Iraq‟s population profile is
characteristic of a developing
country. The bulk of the
population is within the youngest
generations. This indicates
several things: a higher TFR and a
• In the Iraq case, TFR is expected
to drop (from 5.4 to 2.7), but
IMR is also supposed to decline
with the import of new
• Developing nations have a
population profile characterized
by a pyramid-shape, bottom
heavy. In this case the TFR much
greater than 2, and the population
Comparison of Population Profiles:
Developed –v. Developing
Countries (fig 5-17)
Population Trends : Developing
Countries and the DT
• According to the population profiles developing countries will continuously
expand. Is there any hope for decreasing the population growth? Perhaps
through the Demographic Transition (DT).
• The Demographic Transition = model that shows a country's population
trends (fertility and death rate) over the course of industrialization, from
developing to developed.
• The DT occurs in 4 phases
– Phase 1 = primitive stability resulting from high CBR and high CDR. Similar to
hummingbird population on slide 10.
– Phase 2 = with the advent of industrialization and better technology/health
care the CDR drops but the fertility rate stays the same. The population begins
to grow rapidly
– Phase 3 = cultural shift during the latter stages of development. Social and
cultural pressures tend to decrease the fertility rate as a countries progresses
through industrialization. The CDR continues to drop. In this phase, the
population still increases, but the rate of increase slows down.
– Phase 4 = a county is now “developed”, and it is marked by having a stable
population with low fertility and low CDR
Notes about the DT:
• Developed by Warren Thompson (1929) and is based on the population transition
of European nations through the course of industrialization, several centuries. The
timeline for transition has been much faster for some nations, such as the Asian
“Economic Tigers” (e.g. South Korea), but many developing nations seem to be
“stuck” in phase 2.
• Some criticizes of the DT include:
– Based on only European demographics, and not inclusive of all nations
– The supposed cultural shift in phase 3 would have to be applied to every socio-economic
class. If during industrialization the upper and middle income groups would be the first to
experience an increase in resources, the lower socioeconomic classes may not reap the
benefits of industrialization. In this case, the drop in fertility would only occur within select
group; not all groups of people would simultaneously lower their fertility.
– Countries with a large population of subsistence farmers would have difficulties
transitioning into phase 4 simply because they do not have the capitol needed to become
industrialized. Many of the Developing countries would remain in phase 2 with lowered
death rate but stable fertility. Populations in this case would continue to rise, perhaps
acting in a negative feedback loop. Figure 5 -1 9 shows several of these countries.
Real World Data, Figure 5-19
Nations to the left of the dividing line have been “trapped”
in that position for several decades. Why?
Poverty, Fertility, and
Environmental Degradation (fig. 6-
Negative feedback, aka “Vicious
Cycle” (pg 156)
• From your textbook, pg 157:
– A fifth of the world‟s population
(1.2 billion) live on less than
– 1 billion lack access to clean
– 2.4 billion lack access to sanitary
– 800 million + are malnourished
– “..the poor suffer higher rates of
disease, lower life expectancy,
higher infant morality, higher
illiteracy, poor living conditions,
social exclusion, and
powerlessness. In short, the
vicious cycle of high fertility,
poverty, and environmental
degradation persists, presenting
the international community with
an enormous challenge.”
(new section) Perspectives on
• What can be done about the overpopulation problem? Several arguments
have been put forth to explain the consequences of overpopulation. We
won‟t get to every academic camp on population. Instead, in the interest
of time, I am going to focus on the Neo-Malthusians and Cornucopians.
You may wish to add other population perspectives during your bulletin
board discussion, and I encourage you to go beyond these two camps and
research others. For an excellent review of population perspectives (FYI
only, not required reading) see Dr. Keith Montgomery‟s website, which has
multiple links for classical population literature:
• Thomas Malthus (1766 – 1834)
– Mathematician and Anglican minister
– Wrote “An Essay on the Principle of Population as it Affects the Future
Improvement of Society”
• Malthusian view on population is that if 1) humans need food and 2) humans have
sexual desires, then the power of population is indefinitely greater than the power in
the earth to produce subsistence, and therefore, population will increase
• Human population
growth is exponential
growth is arithmetic.
• Eventually population
would outstrip the
• Eventually the power overpopulation
of humans to
reproduce would be
more powerful than
the ability of the Earth
to sustain it
• Consequences of population growth = poverty
– Population growth leads to poverty when the population
increases faster than the food supply.
– Overpopulation leads to lower wages and a labor surplus,
further exasperating poverty
– Malthus believed that the Poor should incorporate “moral
restraint” to curve their high reproductive habits. Poverty is to
be blamed on the Poor. It‟s the Poor's own fault that they are
• The Poor should adopt middle-class values to avoid the
consequences of overpopulation
• Malthus was skeptical that the Poor where capable of doing this
(Social Darwinism), and thus the Poor would remain poor. He
was opposed to welfare because it might encourage more poverty.
Critique of Malthus
• Malthusian ideas have been criticized by other
– One of the biggest criticisms, his interpretation
about the arithmetic increase in the food supply was
incorrect. Food production has skyrocketed in the
last several decades, partly due to increase in
technological advances (e.g. precision agriculture,
development of new resistant crops, embryonic
cyclogenesis, etc.). Food supply has kept pace (and
may have possibly exceeded) human population.
• Two of the more outspoken, and controversial Neo-Malthusians are
– Paul Ehrlich: The Population Bomb
• Seen as a “Doomsdayer” , proposes that unless immediate action is taken to control
overpopulation, series crisis's will ensue.
• “We can no longer afford merely to treat the symptoms of the cancer of population
growth; the cancer itself must be cut out. Population control is the only answer. The
operation will demand many apparently brutal and heartless decisions. The pain may
be intense. But the disease is so far advanced that only with radical surgery does the
patient have a chance of survival”, quote in Schmidtz and Willott (2002),
Environmental Ethics; What Really Matters, What Really Works, Oxford University
Press, New York, pg 265.
– Garrett Hardin: “The Tragedy of the Commons”
• Author of the “Lifeboat Ethics. Quoting Goldfarb (2000) in his book Notable
Selections in Environmental Studies, Second Edition, Dushkin-McGraw Hill, Guilford,
CN,) “[Lifeboat ethics is] a world model in which the develop, affluent nations that
control and use most of the world‟s resources are in a lifeboat while the struggling
developed nations are floundering in the surrounding ocean. He concludes that it is
folly to try to rescue all the swimmers and suggests that the ethically appropriate
strategy is one of triage, by which the „haves‟ permit the poorest and least developed
of the „have nots‟ to drown in order to prevent the entire boat from sinking” (pp. 39-
• A contrasting academic camp to the Neo-
Matlhusians are the Cornucopians.
– Technological advances (e.g. in agriculture) and
expansion of the market economy will mitigate any
problems presented by overpopulation. If there are
more people, then we will discover/invent new ways
to feed them. Technology will help us better utilize
our resources, cure diseases, etc.
– Prominent among the Cornucopians is Bjørn