Human Population Growth Main Topics

Human Population Growth Main Topics

Figure 4

The above graph shows the global population growth of humans since prehistory. Note that until recently the growth of the human population was very slow. However, since the Industrial Age human population growth has accelerated exponentially. Unlike most natural populations, this type of growth is not normally seen. Main reason why human population continues to rise is here.

World Population in Billions with Comparative Demographics of Kenya and the US

A closer look at the recent exponential growth of human populations...

It took all of human history until 1780 for earth's population to reach 1 billion people.
In only 150 years the population had doubled to 2 billion
By 1974 the world population doubled again in less than 45.
In 1988 we added another two billion.
On February 26^th 2006 (at 7:16 PM EST) there were 6.5 billion people on the planet.
The population is expected to reach 7 billion on Oct 18^th 2012. More info here.

The Crude Birth Rate (CBR): Births per 1000 persons
- CBR for US: 3.78m births per year with population at 270m = (3.78/270) * 1000 = 14 or 14/1000
- CBR for Guatemala: 0.43m births per year with population at 12m = (0.43/12) * 1000 = 36 or 36/1000.
- Problems/Caveat: averaged across entire population without regard for age or sex.
Crude Death Rate (CDR): Deaths per 1000 people
- US: 2.43m deaths per year-> CDR= 9/1000
- Guatemala: 0.08m deaths per year-> CDR= 7/1000
- Problems/Caveat: averaged across entire population without regard for age, sex or ethnicity. For example, 9.5% of US are elderly (>65 yr) while only 3.5% for Guatemala. a larger elderly population results in US having a higher CDR.
Natural Change: CBR-CDR
Total Change: Natural Change + immigration - emigration
Rate of Change: Natural Change/1000

(1998 data)	United States	Guatemala
CBR per 1000	14	36
CDR per 1000	9	7
Rate Natural Increase per 1000 (CBR-CDR)	5	29
Percent Rate Natural Increase	0.5	2.9

Total Fertility Rate: Average number of children a woman would have if during her childbearing years she conforms to the age-specific fertility rate for the year she turns 15. For Guatemala the rate is 4.8. For the US the rate is 2.1
- Fertility can be affected by many factors including
  - Contraception
  - Infant death rate
  - Type of society (Industrial, agrarian)
  - Religion
  - Demographic Transition
- Fertility and fecundity should not be confused (fecundity is a physiological limit). Human record is here.
- Replacement Fertility: Fertility rate that where a population will remain stable. For industrial nations the Replacement Fertility hovers around 2 (ours is 2.1).
- Doubling Time: The amount of time in years for a particular population to double. A rough estimation of the doubling time can be calculated by dividing 70 by the percent rate of increase. For the United States this would be 70/0.5 = 140 (it would take 140 years to go from 270m to 540m). For Guatemala the doubling time is 70/2.9 = 24 years!
  
  Survivorship Curves Track the Fate of a Particular Cohort
Population Pyramids (Demographics Graph)

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Selected Pyramids
NOTE: Try the DYNAMIC PYRAMIDS TOO

The Demographic Transition Model