The Human Population

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The Human Population
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Human Population Over Time

• After growing slowly for thousands of years, the
  human population grew rapidly in the 1800s.

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The History of Human Population Growth

• Years Human
• Elapsed Year Population
• 3,000,000 10,000 B.C. (Agricultural Revolution)
  5-10 Million
• 10,000 1 A.D. 170 Million
• 1,800 1800 (Industrial Revolution) 1 Billion
• 130 1930 2 Billion
• 30 1960 3 Billion
• 15 1975 4 Billion
• 12 1987 5 Billion
• 12 1999 6 Billion
• 8 2008 6.7 Billion

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Human Population Over Time
5
Human Population Over Time

• Why was the population able to grow so rapidly
  during this period of time?
• Increases in food production
• Improvements in hygiene that came with industrial
  and scientific improvements

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Enabling Growth

• Agriculture
• About 12,000 years ago, several cultures shifted
  from hunting and gathering to farming.
• Humans became the first and only species ever to
  control our own food supply, and steady
  population growth was the result.
• In the absence of other limiting factors, any
  population will expand to the limit of its food
  supply this happens so reliably that it is
  considered a law of ecology.

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Agricultural Improvements
8
Enabling Growth

• Technology
• The development of agriculture led by turns to
  settlement, division of labor, mathematics,
  literacy, and science.
• By about 1800, major advances collectively
  referred to as the Industrial Revolution were
  occurring.
• Breakthroughs in medicine, nutrition and
  sanitation brought down child mortality rates and
  led to longer life spans.
• The mechanization of agriculture and improvements
  in food preservation led to even greater
  increases in food production and availability.
• Human numbers began doubling at an unprecedented
  pace.

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Rates of Growth

• Past
• A graph of human population before the
  agricultural revolution would likely have
  suggested a wave, reflecting growth in times of
  plenty and decline in times of want, as graphs of
  other species populations continue to look to
  this day.
• The graph of recent human population growth is
  referred to as a "J curve," as it follows the
  shape of that letter, starting out low and
  skyrocketing straight up.

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Rates of Growth

• Present
• World population reached 6 billion people in
  1999, and it is over 6.6 billion in 2007.
• At the present rate of growth over 77 million a
  year, the world adds a New York City every month,
  a Germany every year and a Europe each decade.
• Teen childbearing rates in the US are the highest
  in the developed world and 11 of all US births
  are to teenage mothers.

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Rates of Growth

• The United States, with over 300 million people,
  is growing by more than 2.8 million people each
  year. At this rate, we are one of the fastest
  growing industrialized nations in the world, and
  we have the third largest population of all
  nations, preceded only by China and India.

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Rates of Growth

• Future
• With a current annual growth rate of 1.2, world
  population is projected to double in just 58
  years.
• Our doubling times will be realized if and only
  if growth rates remain constant.
• Today, the world's birth rate is about two and a
  half times its death rate. The closer these two
  rates are, the slower population growth will be.

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Rates of Growth

• Zero population growth is the demographic term
  for the state of equilibrium reached when birth
  and death rates are the same.
• Momentum is also a factor in population growth.
• Some countries, like the U.S., are growing even
  though the average woman has just two children.
• In such cases, a population can still take 60-70
  years to stabilize, and will do so only when the
  percentage of elderly people is equal to the
  percentage at child-bearing age

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Studying Human Populations

• The human population of Earth grew faster in the
  20th century than ever before.
• Demography is the study of populations.
• Demographers study historical size and makeup of
  populations to make comparisons and predictions.

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Demography Cont.

• Demographers also study properties that affect
  population growth.
• Ex economics and social structure
• Countries are grouped into 2 different
  categories
• Developed countries higher average incomes,
  slower population growth, diverse industrial
  economies, strong social support
• Developing countries lower average incomes,
  simple agriculture-based economies, and rapid
  population growth

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Forecasting Population Size

• Population Size is determined by
• Age structure
• Survivorship
• Fertility Rates
• Migration

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Forecasting Population Size

• Age Structure the distribution of ages in a
  specific population at a certain time.
• Countries that have a high rate of growth usually
  have more young people than older people.
• Countries that have a slow rate of growth or an
  even rate of growth usually have an even age
  distribution.

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Population Pyramid
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Forecasting Population Size Cont.

• Survivorship the percentage of members of a
  group that are likely to survive to any given
  age.
• Demographers study a group of individuals that
  were born at the same time and notes when each
  group member dies.
• The results are plotted on survivorship curves.

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Survivorship Curves

• Type I Curves Most people live to old age
• Type II Curves Similar death rates at all ages
• Type III Curves the pattern in very poor human
  populations in which many children die
• Type I and type III survivorship may result in
  populations that remain the same size or grow
  slowly.

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Survivorship Curves
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Forecasting Population Size Cont.

• Fertility Rates the number of babies born each
  year per 1,000 women in a population
• Replacement level the average number of children
  each a parent must have in order to replace
  themselves in a population.
• This number is 2.1 or slightly more than 2,
  because not all children born will survive.
• In 1972, the total fertility rate dropped below
  the replacement rate and remained there for most
  of the 1990s.

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Total Fertility Rate
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Forecasting Population Size Cont.

• Migration the movement of individuals between
  areas
• Immigration movement into an area
• Emigration movement out of an area

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How Have Fertility Rates Changed in the U.S.?

• Between 1910 and 1930, birth rates fell sharply
  as
• the country underwent industrialization and
  urbanization
• More women got an education and began working
  outside the home

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How Have Fertility Rates Changed in the U.S.?

• In the 1930s, the birth rate remained low due to
  the Great Depression and then began rising in the
  1940s during World War II.
• The sharp rise in birth rates after World War II
  is known as the baby boom period when 79 million
  people were added to the U.S. population.
• Between 1956 and 1972, the birth rate began to
  drop as more women began working outside of the
  home.

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How Have Fertility Rates Changed in the U.S.?

• Between 1977 and 2000, a small echo boom in the
  number of births per year occurred as large
  numbers of people born during the baby boom began
  having children.
• According to the U.S. Bureau of Census, the
  population of the U.S. will increase from 288
  million to 414 million between 2002 and 2050 and
  will reach 571 million by 2100.

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Declining Death Rates

• The dramatic increase in Earths population in
  the last 200 years has occurred because death
  rates have declined more rapidly than birth
  rates.
• Life Expectancy the average number of years a
  person is expected to live
• For people in many developed countries life
  expectancy is 80 years

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Life Expectancy
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The Demographic Transition

• Demographic transition the shift from high birth
  rates to low birth rates during industrialization
• This occurs in four stages.

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Stages of Demographic Transition

• 1st Stage preindustrial conditions birth rate
  and death rate are both high and population is
  stable
• 2nd Stage population explosion death rate
  decline as hygiene, nutrition and education
  improve
• 3rd Stage population growth slows as birth rate
  decreases
• 4th Stage birth rate drops below replacement
  rate, so the population begins to decrease

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The Demographic Transition
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Changing Population Trends

• Some countries have reached the demographic
  transition- they have reached large population
  sizes and have increased life expectancies.
• Throughout history, populations that have high
  rates of growth create environmental problems.
• Rapidly growing populations use resources at an
  increased rate and tax infrastructure.
• Infrastructure water supplies, sewer plants,
  power companies, roads, subways, schools and
  hospitals

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Problems of Rapid Growth

• Shortage of Fuelwood
• In many poor countries, wood is the main fuel
  source.
• When populations are stable, people are able to
  use deadwood.
• When populations grow rapidly, deadwood does not
  accumulate fast enough.
• This results in forests being cleared of
  vegetation.

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Problems of Rapid Growth

• Unsafe Water
• In some areas of the world, the local water
  supply may be used not only for drinking water
  and washing but also for sewage disposal.
• The water systems many cities cannot keep up the
  rapidly expanding populations.
• In 2001, nearly 1 billion people lacked adequate
  drinking water and 3 million died from diseases
  that were spread through water.

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Density vs. Consumption

• Water Pollution
• In the U.S., 40 of streams, 45 of lakes, and
  50 of estuaries are unfit for swimming or
  fishing.
• Agricultural chemicals, eroded sediment, and
  animal wastes have fouled over 173,000 miles of
  waterways.
• Almost 45 of our drinking water comes from
  groundwater sources, and 38 states reported
  finding pesticides, some carcinogens, in their
  groundwater.

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Unsafe Drinking Water
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Problems of Rapid Growth

• Impacts on Land
• Growing populations have shortage of arable land
  (land that is suitable for growing crops)
• Growing populations make tradeoffs between using
  land for agriculture, housing, or natural
  habitats.
• Much of the world is undergoing urbanization
  resulting in suburban sprawl.

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Density vs. Consumption

• Land Use
• In the last 200 years the United States has lost
  at least 71 of its topsoil, 50 of its
  wetlands, 90 of its northwestern old-growth
  forests, and 99 of its tall grass prairie.
• In the United States, more than 8,000 square
  miles of land per year disappear under suburban
  sprawlmost often land of superior quality for
  agriculture

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Density vs. Consumption

• Degree of Impact
• The impact of any human group on its environment
  has to do with three equally important factors.
• The first is the number of people.
• The second factor encompasses the ways in which
  we manufacture goods, design communities, and use
  technology.
• The third is the actual amount of resources
  consumed by each person.
• Unfortunately, the rate at which industrialized
  nations consume resources makes their
  populations' effect on the planet vastly greater
  than that of developing countries.

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Density vs. Consumption

• Energy
• Americans constitute less than 5 of the world's
  population, but are responsible for nearly 23 of
  the world's annual energy consumption, including
  25 of fossil fuels.
• On average, one American consumes as much energy
  as 2 Germans, 7 Syrians, 12 Columbians, 24
  Indians, 100 Haitians, or 286 Ethiopians.

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Global Energy Consumption
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Density vs. Consumption

• Natural Resources
• A person living in an industrialized country
  consumes twice as much grain, three times as much
  meat, nine times as much paper and eleven times
  as much gasoline as someone in a developing
  country.
• North America, with 5 of the worlds population,
  consumes 30 of the aluminum

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Global Natural Resource Use
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Density vs. Consumption

• Global Warming
• In 2004, the U.S. was responsible for 22 of the
  worlds carbon dioxide emissions, more than any
  other country.
• China, with over four times more people than the
  U.S., produces less than 80 of the carbon
  dioxide that the U.S. produces, but their CO2
  output has been growing steadily over the past
  decade.
• Carbon dioxide is the primary greenhouse gas,
  responsible for 60 of global warming caused by
  greenhouse gases.

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Global Carbon Dioxide Production
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Density vs. Consumption

• Waste
• The more we consume, the more waste we produce.
  By the time a baby born today in the United
  States reaches the age of 82 years, he or she
  will have produced at least 60 tons of garbage.
• The average American generates 4.4 lbs. of solid
  waste each day.
• Average people in France produce 2.9 pounds and
  in South Africa 1.5 pounds, while residents of
  Egypt and Pakistan produce less than 1 pound per
  day.

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Managing Development and Population Growth

• Countries such as Thailand, China, and India have
  created campaigns to reduce fertility rates in
  their citizens.
• These campaigns include family planning programs,
  public advertising, economic incentives, and
  legal punishments.

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WORLD POPULATION GROWTH SOLUTIONS

• Making sure people around the world have access
  to family planning services.
• Empowering women in developing countries
  economically, socially, and legally in a manner
  that results in them having an equal say (with
  their husbands) in reproductive decisions.
• Modifying school curricula to include information
  on population levels and implications for the
  future.
• Reforming tax laws in a way that encourages
  couples to have no more than two children. (They
  would still be able to have as many kids as they
  want, but the tax code would no longer subsidize
  more than two.)