The Human Population
Human Population History:
Human Population facts:
2,000 years ago the estimated human population was 150 million
By 1850, the human population was one billion. By 1930, it was 2 billion.
It took 10,000 generations to reach 2 billion.
The human population is now growing at a rate of about 3 people/second
or 260 thousand/day or 1.8 million per week or 93 million/year
Every 3 years, the global environment must support another 285 million
Even the U.S. population is growing fast. We're currently adding the equivalent
of three Washington, D.C.s every year; another New Jersey every 4 years.
U.S. at night
How many of us are there? Click on the rotating Earth!
As a result of this rapid growth:
Approximately 1.3 billion of the world's people are impoverished, living
on the equivalent of less than 1 dollar a day. And as population steadily
increases, the gap between rich and poor is widening.
Some 60% of the 4.8 billion people in developing countries lack basic sanitation,
and almost one-third have no access to clean water.
Nearly 1 billion people in the world are illiterate, two-thirds of them
Despite increases in grain production that began in the 1950s, thanks to
"miracle wheat" and other advances in agricultural technology,
such increases seem to have leveled off in recent years. Some 841 million
people today are chronically malnourished, and there are 88 "food deficit"
countries. This means "they can neither feed themselves nor afford the
imports they need," according to the United Nations Population Fund, a
subsidiary of the UN General Assembly and the largest internationally-funded
source of population assistance to developing countries.
When a country darkens on this map, it represents a death
caused by hunger.
Supplies of water for irrigation are declining around the world as underground
water reserves - aquifers - become depleted faster than nature can fill
them. Groundwater overdrafting is now widespread in the crop-producing
regions of central and northern China, northwest and southern India, parts
of Pakistan, much of the Western United States, North Africa, the Middle
East, and the Arabian Peninsula.
Nearly half the earth's land mass already has been changed by human activity
- wetlands filled in, forests cut down, prairies plowed under. Runoff from
farms, industries, and urban areas has resulted in some 50 "dead zones"
Among the ocean's 200 major fish
stocks, 35% are in decline, and another 25% are being fully exploited.
Species are going extinct at a faster rate than ever before, including
the time when dinosaurs were dying out.
Factors Contributing to the Population Explosion:
The green revolution
Agricultural advances have insured that no one
has to starve. For thousands of years, the Earth's carrying capacity depended
on the available food supply. That is no longer the case.
Advances in medicine
Disease has throughout history always been the
definitive factor in the limiting of the human population. However, medical
research has largely controlled (or eliminated) such diseases as smallpox,
malaria, & cholera. As a result, death rates have declined dramatically.
The industrial revolution
An increase in the availability and use of technology
has lead to a more densely packed society that attempts to make room for
an ever increasing population. The influx of new technology into the global
market over the past 150 years has made life generally easier in the industrialised
nations of the world and led to promising social situations that provoke
the tendency of people to have more children.
In some countries people lack awareness of birth
control or the ability to limit the size of their families. Recent United
Nations statistics indicate that 90% of women in 10 African nations had
not heard of contraception.
People in some developing countries who do want to
limit the growth of their families lack access to contraception or reproductive-health
services. Family planning methods are simply not available in large sections
of the world. As many as 500 million women in developing countries live
too far from health centers to obtain contraceptives, & unsafe abortions
kill an estimated 70,000 women a year.
Human reproduction is a matter of great religious
and cultural importance as well. The religious teachings of many people
prohibit or discourage contraception. And some cultures traditionally value
large families as a sign of prestige and power.
The overall rate of population increase depends on the number of births
and deaths, but also on the length of generations -- the age at which women
have their first baby.
For example, if all women had three kids with a 15-year average generation
time, the rate of population growth would be 2.7%. If the average spacing
were 30 years, the growth would drop in half -- to 1.35%.
How does percent population growth translate into 'doubling
Population Age Structure:
Birth and death rates do not tell the whole story of population growth.
A country's TFR can be below replacement level while the population continues
to grow, if there are a disproportionately large number of couples in these
younger age groups. That is the situation in Kenya and, to a lesser degree,
the United States. The age structure of the population, then, is also an
important factor in population change (see the population pyramids for
Kenya, Sweden, & the U.S. above). When a substantial proportion of
a country's population is young, high population growth rates in a country
are to be expected, even if the average TFR is modest. The reason is that
so many females are of childbearing age, that even a modest average
TFR results in a large number of births.
Replacement-level fertility = the number of children
a couple must bear to replace themselves
slightly more than 2 children because some children
die before reaching their reproductive years
reproducing at this level does NOT mean that population
growth stops; there are so many "future parents" already alive that, even
at replacement-level, population will continue to grow for many years
Total fertility rate (TFR) - estimate of the average
number of children a woman will have during childbearing years
In 1995, the TFR was 3.1 children per woman (1.6
in MDCs & 3.5 in LDCs); still far above replacement level
This map shows the average number of children born to
a woman during her lifetime. The darker the color, the greater the
number of children. For example, France at 1.7 children
has a lower fertility rate than Egypt at 3.6 children. The total fertility
rate (TFR) is the average number of children a woman
would have, assuming that current age-specific birth
rates will remain constant throughout her childbearing
years (usually considered to be ages 15-49).
Fertility rates in the United States:
Peaked in 1957 at 3.7 children/woman
At or below replacement level (2.1) since about 1972
widespread use of birth control
availability of legal abortion
social attitudes favoring small families
increasing cost of raising a child to age 18 ($177,000
for low-income family, $231,000 for middle-income & $335,000 for upper-income)
increase in average age of marriage between 1958
& 1992 (from 20 to 24.4 for women, and from 23 to 26.5 for men)
More women working outside home (child-bearing rate
of "working" women 1/3 that of women not in paid labor force)
The U.S. population is still growing faster than most MDCs:
In 1995, the U.S. population grew by 1.18% (3.1 million people) more than
double mean rate of world's industrialized nations.
The U.S. population is projected to increase from 263 million to 345 million
between 1995 & 2030, with no leveling off anticipated
This projected growth of the U.S. population is due to:
large number of baby boomer women still in child-bearing years (i.e., lots
of potential mothers)
increase in number of unmarried mothers (including teen-agers)
higher fertility rates for women in some racial & ethnic groups than
for Caucasian women
high levels of legal/illegal immigration (about 40% of current growth)
U.S. population growth is very important because of the impact that each
of us has on the environment. For example:
Earth's Carrying Capacity (is the Earth overpopulated?):
Carrying capacity is the number of organisms an environment (e.g., the
Earth) can support
determined by: food production, living space, waste assimilation, &
for humans, carrying capacity can be expanded through advances in agriculture,
industry, & medicine
Some believe Earth's carrying capacity has already been exceeded as illustrated
The world's marine catch has increased more than four times in the past
40 years -- from 18.5 million tons in 1950 to 82.5 million tons by 1992.
This staggering growth has resulted in overfishing and wasteful, destructive
fishing practices worldwide which now threaten the lives of hundreds of
millions of people who are vitally dependent on fishing for food and livelihoods.
They face resource depletion, competition from industrial and distant water
fleets, and loss of access to traditional marine food supplies.
Continued forest loss and degradation will have serious implications at
local, regional, and global levels. Exploitation and clearance of natural
forests are destroying the environment and way of life for tens of thousands
of indigenous people. Disappearing forest cover also represents incalculable
losses in biological diversity and ecological services, including nutrient
recycling, watershed management, and climate regulation.
Percentage of Tropical Forest
Cleared by Region Between 1960 and 1990
and so on
Others are more optimistic & believe Earth could support many more
More people = more productivity = more knowledge = better production methods
+ discovery of new substitutes, and so on
Impacts of continued growth in human populations include:
increased hunger/starvation while food production levels off or even declines
(i.e., less food/person)
|While grain yields per acre have been increasing
steadily until 1990, the rate of increase has fallen off in the last
10 years. Most of the benefits of irrigation, machinery, fertilizer and
plant breeding have already been realized. The production of grain per
acre is close to the maximum obtainable through photosynthesis. Geneticists
are working on improving the efficiency of photosynthesis, and that may
turn out to be possible, but given that nature has been working on the
problem for several hundred million years, there is no guarantee that we
can improve on the process in the next 10 to 20 years.
for more information.
Desertification is the conversion of productive rangeland or cropland into
desertlike land. It is usually caused by a combination of overgrazing,
soil erosion, prolonged drought and climate change.
Arable land per person
increased number of refugees
Cities may offer opportunities for the people of developing countries.
However, the danger lies in the structural inadequacies typical of many
cities in these countries. The most obvious of these inadequacies are those
of public sanitation. Insufficient or non-existent sewage systems in exist
in many parts of these cities. Water supplies can thereby become polluted,
leading to the high incidences of disease.
dying seas & rivers, for example:
Where are we headed?:
Maximum Global Population Guesses (McCluney
|Everyone at the current U.S. standard of living and with
all the health, nutrition, personal dignity and freedom that most Americans
|Everyone at the same affluence as the U.S. (current),
but with many and onerous restrictions on freedoms relative to behaviors
leading to environmental degradation. To accommodate populations greater
than 2 billion, restrictions such as the following would have to be instituted:
Driving restrictions (gasoline rationing, fuel rationing
even to mass transit systems).
Restrictions on the transport of food (food transported no
more than 100 miles for example to its point of retail sales).
Prohibitions against cutting trees on one's property.
Limitations on the burning of fossil fuels to save these
complex molecules for more valuable or durable uses, such as in the manufacture
of plastics and pharmaceuticals.
Limitations on the areas of open spaces that can be converted
to renewable energy power plants, such as solar thermal, solar photovoltaic,
and wind energy systems. This latter results from the need to preserve
natural areas for food growing.
|Only people in the U.S. and Europe at current level of
affluence. Everyone else at the current prosperity level of Mexico.
|Everyone in the world at Mexico's current prosperity
|Everyone in the world at the current "prosperity"
level of northwest Africa.
Text of the message of Secretary-General Kofi Annan to mark World Environment
Day, 5 June 2000:
We may be at the dawn of a new millennium, but the environmental problems
we face are painfully familiar. They may even be
getting worse. Despite the Earth Summit, and despite success stories
like the Montreal Protocol to protect the Ozone Layer,
human beings continue to plunder the global environment. Unsustainable
practices remain deeply embedded in the fabric of our
daily lives. We are failing to protect resources and ecosystems. We
are failing to invest enough in alternative technologies,
especially for energy. We are failing even to keep the debate alive.
These are deeply troubling trends. I recommend four priorities for reversing
Technological breakthroughs that are unimaginable today may well solve
some of the environmental challenges we face. But it
First, we need a major public education effort. Understanding of the challenges
we face is alarmingly low. Corporations and consumers alike need to recognize
that their choices can have significant consequences. Schools and civil
society groups have a crucial role to play.
Second, environmental issues must be fundamentally repositioned in the
policy-making arena. The environment must become better integrated into
mainstream economic policy, and the surest way is through green accounting.
Third, Governments must not only create environmental agreements, they
must enforce them. They can, for example, cut the subsidies that sustain
environmentally harmful activities each and every year. They can also devise
more environment-friendly incentives for markets to respond to.
And fourth, we need sound scientific information. This is the only basis
for effective policy, yet large gaps in our knowledge remain.
would be foolish to count on them and to continue with business as
usual. The theme for this year's World Environment Day
says it best: the year 2000 begins the environment millennium; the
time to act is now. There will be no easy solutions.
Unpleasant ecological surprises lie ahead. But the start of the new
century could not be a more opportune time to commit
ourselves -- peoples as well as governments -- to a new ethic of conservation
Why six billion?
to BIO 599/799 Syllabus