Human Populations
Inputs and Outputs of Human Population
Inputs:
- Births: The arrival of new individuals in the population through reproduction.
- Immigration: Movement of individuals into a population from other regions or countries.
Outputs:
- Deaths: The number of individuals who die in a population.
- Emigration: Movement of individuals out of a population to other areas or countries.
Population Dynamics and Its Calculation
Population dynamics is the study of changes in population size and structure over time, influenced by birth rates, death rates, immigration, and emigration.
Total Fertility Rate (TFR)
The Total Fertility Rate represents the average number of children a woman would have over her lifetime if current age-specific fertility rates remained constant. It's a more refined measure than CBR as it accounts for age structure.
NoteA TFR of about 2.1 is considered the replacement level in developed countries, meaning the population would remain stable (not accounting for migration).
Doubling Time (DT)
Doubling Time is the period required for a population to double in size, assuming a constant growth rate. It's calculated using the "Rule of 70":
๐ท๐= 70/Annual growth rate (%)
ExampleIf a population has a 2% annual growth rate, its doubling time would be:
๐ท๐ = 70/2 = 35 years
Natural Increase Rate (NIR)
The Natural Increase Rate is the difference between the birth rate and death rate, expressed as a percentage:
๐๐ผ๐ =(๐ถ๐ต๐ โ๐ถ๐ท๐ )รท10
TipRemember that NIR doesn't account for migration, which can significantly affect population change in some regions.
Population models
The global human population has followed a rapid growth curve. Models are used to predict the growth of the future global human population.
Age-sex pyramids
The existing population can be modelled using age-sex pyramids. The pyramid is measured in absolute numbers or as a percentage of the total population. It shows the proportion of the population of either gender in each age group
The demographic transition model (DTM)
DTM is a model that explains the transition of a countryโs population from high birth and death rates to low birth and death rates as it develops economically and socially.
Stages of the DTM:
- Stage 1 (Pre-Industrial): High birth rates, high death rates, and low population growth.
- Stage 2 (Transitional): High birth rates, and falling death rates due to improvements in healthcare and sanitation.
- Stage 3 (Industrial): Declining birth rates, low death rates, slowing population growth.
- Stage 4 (Post-Industrial): Low birth and death rates, stable or slowly growing population.
- Stage 5 (Declining): Very low birth rates, low death rates, and potential population decline.
The DTM is a generalized model and doesn't perfectly fit all countries' experiences. Some countries may skip stages or experience them differently.
TipYou should be able to give examples of countries in different stages of the DTM with reasons.
Policies to manage human population growth
Pro-Natalist Policies:
- Encourage higher birth rates through incentives such as child benefits, tax relief, and subsidized childcare.
- Common in countries with low birth rates and ageing populations.
Anti-Natalist Policies:
- Aim to reduce birth rates through measures such as family planning programs, education, and access to contraception.
- Examples include Chinaโs former one-child policy and Indiaโs family planning programs.
Migration Policies:
- Regulate immigration and emigration to balance population growth and reduce pressure on local resources.
