HUMAN POPULATIONS

World Population Over the Centuries

9,000 human beings added to the planet every hour

Exponential Growth

• Exponential growth is marked by doubling. A few doublings can lead quickly to enormous numbers.

• It is deceptive because it starts out slowly, but rapidly gets out of hand.

Exponential Grwoth

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Money Series1

Series2

Reasons for the Human Population Explosion

• Causes of disease recognized• Improvements in nutrition• Discovery of antibiotics• Improvements in medicine• Increase in number of women who actually

reach child-bearing age• Short doubling times in some countries• Increased food production• Sanitation

What influences Growth rate?• Crude birth rate – the number of

births per thousand people.

• Crude death rate – the number of deaths per thousand people.

– If they are equal, there is zero population growth.

– If births is higher than deaths, then the pop. Goes up.

– Life expectancy – The average number of years someone is expected to live.

Calculating Fertility Rates and Doubling Times(CBR - CDR)/1000 x 100 =

% Rate of Increase or decrease in population per 1000 per year

70/ Rate of Increase = Doubling Time

Doubling time- The time it takes for the population to double the number of people

Growth Rate- includes birth rate, death rate, immigration and emigration

Factors Affecting Death Rates• Death rates have declined because of:

– Increased food supplies, better nutrition.– Advances in medicine.– Improved sanitation and personal hygiene.– Safer water supplies.

• U.S. infant mortality is higher than it could be (ranked 46th world-wide) due to:– Inadequate pre- and post-natal care for poor.– Drug addiction.– High teenage birth rate.

Infant mortality rate- Number of child/infant deaths.

If a mother lives in an area with a high infant mortality rate she will tend to have a lot of children to ensure some will make it to adulthood.

Zero Population Growth- When the number of births, equals the number of deaths. No growth in the population.

Total Fertility Rate- an estimate of the average number of children a women will have during her childbearing years.

Factors that affect birth & fertility rates

• Importance of kids in labor force

• Urbanization• Cost of raising &

educating kids• Availability of private

& public pensions• Religious beliefs,

traditions & cultural norms

• Educational & employment opportunities

• Infant mortality rate• Average age at

marriage• Availability of reliable

birth control

Replacement-level fertility- the number of children a couple must bear to replace themselves. It is slightly higher than two children per couple. (2.2 in developed countries and as high as 4.5 in some developing countries)

It is greater in countries w/ high infant mortality rates than in countries w/ low infant mortality rates

Factors Affecting Birth Rates and Fertility Rates

• The number of children women have is affected by:– The cost of raising and educating them.– Availability of pensions.– Urbanization.– Education and employment opportunities.– Infant deaths.– Marriage age.– Availability of contraception and abortion.

Other factors that influence a countries population

• Immigration – the migration or movement of people into a country or area to take up permanent residence.

• Emigration – the migration or movement of people out of a country.

• Net Migration- Total number of people moving into or out of the population.

Reasons to Immigrate

1. Work2. Money3. Political Safety4. Freedom of Religion5. To Escape War 6. Famine7. For a Better Education8. Different Government9. Tolerance

• Usually people immigrate to start a better life for them or their families. Some come alone in hope that they can soon bring the rest of their family. Others work so they can send money to help those where they came from.

FACTORS AFFECTING HUMAN POPULATION SIZE

• Population increases because of births and immigration and decreases through deaths and emigration.

• Instead of using raw numbers, crude birth rates and crude death rates are used (based on total number of births or deaths per 1,000 people in a population).

Demographics

• A demographer studies vital statistics about people, such as birth rates, death rates, where they live, as well as population size.

• They compare country to country, state to state, region to region.

• They can predict trends that can be important to plan the future.

Demographics

• Developed– High literacy rates– High standards of living– Low birth rate– Low death rate– Slow or Zero population

growth– High life expectancy– Rich– High per capita– High Energy Consumption– Urban populations

• Less-Developed– Low literacy rates– Low standard of living– High birth rate– High death rate– Rapid population growth– Low life expectancy– Poor– Widespread Disease– Low per capita– Rural populations

Economic Categories Based on Per Capita Gross National Income

• Gross National Product (GNP)- The most commonly used measure of the economic growth of a country.

per capita – takes into relation countries population

• High-income, highly developed, industrialized countries– United States, Japan, Canada– Average GNI per capita = $26,710

• Middle-income, moderately developed countries– Latin America, South Africa, China– Average GNI per capita = $1,850

Major Economic Divisions of the World

Gross national income/capita

The Poverty Cycle

Poor (less developed) countries have high population growth rates therefore, high populations.

More developed (richer) countries have little or no population growth.

Histograms• These population histograms show the

age distribution and help predict the age dist. for the future.

10 years later

• The age structure histogram below shows the percentage of population for both male (left) and female (right) for three nations, Mexico (rapid growth), U.S. (slow growth) and Sweden (zero growth). The shaded areas on each graph show people in their child bearing years.

Age structure- Percentage of the population at each age

level in a population

Generation time- the time it takes for 1 generation to pass.

POPULATION AGE STRUCTURE

• The number of people in young, middle, and older age groups determines how fast populations grow or decline.

• The number of people younger than age 15 is the major factor determining a country’s population growth.

• Changes in the distribution of a country’s age groups have long-lasting economic and social impacts.

POPULATION AGE STRUCTURE

• Populations with a large proportion of its people in the preproductive ages 1-14 have a large potential for rapid population growth.

Figure 9-9Figure 9-9

POPULATION AGE STRUCTURE

• Today, baby boomers make up nearly half of all adult Americans and dominate the populations demand for goods and services.

Figure 9-11Figure 9-11

SOLUTIONS: INFLUENCING POPULATION SIZE

• Demographic Transition: As countries become economically developed, their birth and death rates tend to decline.– Preindustrial stage: little population growth

due to high infant mortality.– Transitional stage: industrialization begins,

death rates drops and birth rates remain high.– Industrial stage: birth rate drops and

approaches death rate.

• Demographic Transition

SOLUTIONS: INFLUENCING POPULATION SIZE

• Generalized model of demographic transition.– Some developing countries may have difficulty making

the demographic transition.

Figure 9-14Figure 9-14

Population Density

Carrying Capacity

• At this point, the environment can no longer provide for the species, due to a number of different environmental resistances, including food, crowding, competition, etc. The population, due to lack of resources, will begin to die out, allowing the environment to recover. As the environment recovers, the species population is able to flourish once more. This leads to a fluctuation between the prosperity of the species and the prosperity of the environment (hence the fluctuations in the graph). 

Biotic potential – if resources were unlimited, optimal conditions.

Effects of Overpopulation?

• Food Shortage - famine

• Natural recourses shortage

• Land Overuse• War• Disease• Pollution-waste

managment

Consequences of Exploding Populations

More PopulationCauses

MORE

LESS

deforestationresource depletionloss of agricultural landbiodiversitydiseasepest resistancepopulation migrationirrigationwetlands

Population Control

• Psychological/Behavioral: abstention, calendar rhythm method

• Mechanical: condoms, diaphragms

• Chemical: the pill, Norplant

• Surgical: tubal ligation, vasectomy

• Intrauterine Devices (IUD): abortion device

• An important example of mandated population control is China's one-child policy, in which having more than one child is made extremely unattractive. This has led to allegations that practices like infanticide, forced abortions, and forced sterilization are used as a result of the policy.

China’s Family Planning Program

• Currently, China’s TFR is 1.6 children per women.

• China has moved 300 million people out of poverty.

• Problems:– Strong male preference leads to gender

imbalance.– Average population age is increasing.– Not enough resource to support population.

% Increase= (Final Total – Initial Total)/ Initial total x 100

70/ Rate of Increase = Doubling Time

(CBR - CDR)/1000 x 100 = % Rate of Increase or decrease in population per 1000 per year

CB(D)R per 1000 = (# Births / Total Population) x 1000

Chapter 18

Environmental Hazards and Human Health

RISKS AND HAZARDS

• Risk is a measure of the likelihood that you will suffer harm from a hazard.

• We can suffer from:– Biological hazards: from more than 1,400

pathogens.– Chemical hazards: in air, water, soil, and food.– Physical hazards: such as fire, earthquake,

volcanic eruption…– Cultural hazards: such as smoking, poor diet,

unsafe sex, drugs, unsafe working conditions, and poverty.

Transmissible Disease

• Pathway for infectious disease in humans.Figure 18-4Figure 18-4

Transmissible Disease

• WHO estimates that each year the world’s seven deadliest infections kill 13.6 million people – most of them the poor in developing countries.

Figure 18-5Figure 18-5

Case Study: Malaria – Death by Mosquito

• Malaria kills about 2 million people per year and has probably killed more than all of the wars ever fought.

Figure 18-7Figure 18-7

Case Study: Malaria – Death by Mosquito

• Economists estimate that spending $2-3 billion on malaria treatment may save more than 1 million lives per year.

• Window screens, predatory fish, vitamins, and pesticides.

Figure 18-6Figure 18-6

CHEMICAL HAZARDS

• A toxic chemical can cause temporary or permanent harm or death.– Mutagens are chemicals or forms of radiation

that cause or increase the frequency of mutations in DNA.

– Teratogens are chemicals that cause harm or birth defects to a fetus or embryo.

– Carcinogens are chemicals or types of radiation that can cause or promote cancer.

LD50 – Lethal dose 50%

• A helpful measurement for comparing the harmful effects of different chemicals.

• By quantifying the LD50 value for a new chemical, scientist can compare the value to thousands of previous tests.

• They can determine whether a new chemical is more or less lethal in comparison to other chemicals that are being used.

Effects of Chemicals on the Immune, Nervous, and Endocrine

Systems• Long-term exposure to some chemicals at low

doses may disrupt the body’s:– Immune system: specialized cells and tissues

that protect the body against disease and harmful substances.

– Nervous system: brain, spinal cord, and peripheral nerves.

– Endocrine system: complex network of glands that release minute amounts of hormones into the bloodstream.

Case Study: A Black Day in Bhopal, India

• The world’s worst industrial accident occurred in 1984 at a pesticide plant in Bhopal, India.– An explosion at Union Carbide pesticide plant in

an underground storage tank released a large quantity of highly toxic methyl isocyanate (MIC) gas.

– 15,000-22,000 people died– Indian officials claim that simple upgrades could

have prevented the tragedy.

TOXICOLOGY: ASSESSING CHEMICAL HAZARDS

• Factors determining the harm caused by exposure to a chemical include:– The amount of exposure (dose). – The frequency of exposure.– The person who is exposed.– The effectiveness of the body’s detoxification

systems.– One’s genetic makeup.– Current health status

TOXICOLOGY: ASSESSING CHEMICAL HAZARDS

• Estimating human exposure to chemicals and their effects is very difficult because of the many and often poorly understood variables involved.

Figure 18-11Figure 18-11

TOXICOLOGY: ASSESSING CHEMICAL HAZARDS

• Children are more susceptible to the effects of toxic substances because:– Children breathe more air, drink more water, and

eat more food per unit of body weight than adults.– They are exposed to toxins when they put their

fingers or other objects in their mouths.– Children usually have less well-developed immune

systems and detoxification processes than adults.