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CHAPTER 8

The Human Population

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World population over the centuries

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How many people can the Earth support?• The number of people the Earth can support depends

on the living standard we are willing to accept

• Many more people can be supported if we don’t eat meat, don’t travel, don’t heat or A/C our homes, etc.

• For all 7 Billion of us to enjoy a 21st century American way of life, we would need many more Earths!• So the real human carrying capacity is unknown.• Your text suggests 7.7 Billion.

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How have we gotten to 7 Billion?

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The Agricultural Revolution

• Agriculture began 10,000-12,000 years ago.

• Better, more reliable nutrition meant less starvation and better resistance to infection.

• More people survived and reproduced.

• They needed more children to help on the farms.

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The Industrial Revolution• Began in 1800s with coal and then the steam engine• Coal, oil, and natural gas let people do much more work

than by human or animal power

• Cars, planes, cranes, bulldozers, huge fishing boats

• This easy energy lets people do more work, but it has also produced pollution and allowed resource exploitation

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The medical revolution• Before the early 1800s, human populations grew

slowly and fluctuated• Diseases (smallpox, diphtheria, measles, scarlet

fever) hit infants/children hardest• Epidemics (e.g., cholera, black plague) killed millions

• So high reproductive rates were offset by high death rates (mainly from diseases), resulting in a low population growth rate

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Many diseases were vanquished• 1797 Edward Jenner produced the first reliable vaccine

• 1800s Louis Pasteur showed that many diseases were caused by specific infectious agents (bacteria, viruses, fungi) & transmitted via water, food, insects, rodents

• Spectacular decreases in child and infant mortality boosted population growth• Vaccinations• Cities treating sewage and drinking water• Penicillin (and other antibiotics) starting in late1940s• Nutritional improvements

• Availability of contraceptives in developed nations.

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Developed vs. developing countries

• Developed countries: high-income, industrialized nations. The U.S., U.K., Canada, Japan, Australia, Germany, Sweden, etc.

• Developing countries: most low-income nations. Afghanistan, India, Iraq, Iran, Haiti, many others. China and India are transitioning, because of a rising middle class in China and India.

• There is disparity of wealth between countries.

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Fertility rates

• Total fertility rate (TFR) is the number of children the average woman will have during her lifetime.

• TFR has dropped worldwide, to 2.6 now.• In developed countries, the TFR averages 1.6

• The U.S. : TFR ~2.0

• In developing countries, the TFR averages 2.8• These populations will likely continue growing

• It is projected that 90% of all people will live in developing nations by 2075

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Total fertility rate, United States, 1920-2008

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Projecting future populations: a developed country (here, Italy).

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Projecting future populations for developing countries (Burkina Faso, for ex.)

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Comparing projected populations

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Population momentum• Population momentum: the tendency of a population to

increase for a while, even though TFR is reduced to 2 or less.

• This is analogous to hitting the brakes when the light turns red. You can’t stop instantly.

• Age structure of the population is key: The more young people you have, the more reproduction.

• A stable population will be obtained only when the population has been at replacement level fertility (TFR=2.0) for decades!

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The demographic transition• Modernization results in lower death rates, better

health care, declining fertility rates• Undeveloped societies have stable populations

• High birth rates and infant and childhood mortality rates

• Developed societies have stable populations• Low birth rates and infant and childhood mortality

rates

• Demographic transition: a shift in birth and death rates from the primitive to the modern condition in industrialized societies

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Birth and death rates• Crude birth rate (CBR): the number of births per

thousand people per year• Crude death rate (CDR): number of deaths per

thousand people per year• No consideration for age, gender

• CBR – CDR = natural increase (decrease) per 1,000 per year

• Zero-growth occurs when CBR = CDR• With no net migration

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Epidemiologic transition

• Most of human history had high crude death rates

• Death rates in Europe and North America gradually declined by the middle 1800s

• At present, most mortality is from cancer, cardiovascular disease, and other degenerative diseases

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Phases of the demographic transition• Phase I: primitive stability

• High CBR is offset by high CDR

• Phase II: epidemiologic transition. • Better health care means a declining CDR• But a high CBR results in rapid population growth

• Phase III: Fertility rates decline• Population growth is still significant

• Phase IV: modern stability is reached• CDR and CBR are both low

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The demographic transition