A changing human population

A Changing Human A Changing Human PopulationPopulation

Environmental ScienceEnvironmental Science

Studying Human PopulationsStudying Human Populations

DemographyDemography – the study of the – the study of the characteristics of populations (usually characteristics of populations (usually human populations)human populations)

Countries are divided into 2 categories by Countries are divided into 2 categories by demographers:demographers:• DevelopedDeveloped – higher average incomes, slower – higher average incomes, slower

population growth, diverse industrial population growth, diverse industrial economieseconomies

• DevelopingDeveloping – lower average incomes, rapid – lower average incomes, rapid population growth, agriculture-based economypopulation growth, agriculture-based economy

Forecasting Population SizeForecasting Population Size

Demographers try to predict what Demographers try to predict what will happen to a population in order will happen to a population in order to plan for future infrastructure and to plan for future infrastructure and servicesservices

Demographers look at several Demographers look at several different factors to make their different factors to make their predictionspredictions

Age StructureAge Structure

Age structureAge structure describes the distribution of ages describes the distribution of ages of a populationof a population

Countries with high growth rates have more Countries with high growth rates have more young people than old peopleyoung people than old people

Countries with slow growth or no growth have an Countries with slow growth or no growth have an even distribution of ages in the populationeven distribution of ages in the population

SurvivorshipSurvivorship The percentage of The percentage of

members of a group members of a group that are likely to that are likely to survive to a given agesurvive to a given age

To predict To predict survivorship, survivorship, demographers study a demographers study a group of people born group of people born at the same time and at the same time and notes when each notes when each member of the group member of the group dies.dies. Age

Fertility RatesFertility Rates

The number a babies born each year per The number a babies born each year per 1000 women of childbearing age (15-44)1000 women of childbearing age (15-44)

Replacement levelReplacement level – the average – the average number of children parents must have to number of children parents must have to “replace” themselves “replace” themselves

Declining Death RatesDeclining Death Rates

Increased access to food, clean Increased access to food, clean water, and safe sewage disposal water, and safe sewage disposal have lead to a decrease in the world have lead to a decrease in the world death ratedeath rate

This decrease has more to do with This decrease has more to do with the huge increase in the human the huge increase in the human population than the birth rate. population than the birth rate.

MigrationMigration MigrationMigration in general, is any movement of in general, is any movement of

individuals or populations from one location to individuals or populations from one location to another.another.

The populations of many developed countries The populations of many developed countries might be decreasing if not for immigration.might be decreasing if not for immigration.

Declining Death RatesDeclining Death Rates The dramatic increase in EarthThe dramatic increase in Earth’’s human s human

population in the last 200 years has population in the last 200 years has happened because death rates have happened because death rates have declined more rapidly than birth rates.declined more rapidly than birth rates.

Death rates have declined mainly because Death rates have declined mainly because more people now have access to adequate more people now have access to adequate food, clean water, and safe sewage food, clean water, and safe sewage disposal.disposal.

The discovery of vaccines in the 20th The discovery of vaccines in the 20th century also contributed to the declining century also contributed to the declining death rates.death rates.

Life ExpectancyLife Expectancy The average number of The average number of

years that a member years that a member of a population is likely of a population is likely to liveto live

Infant mortality rates Infant mortality rates have the largest have the largest influence on life influence on life expectancy numbersexpectancy numbers

Better medical care Better medical care has lead to higher life has lead to higher life expectancy in expectancy in developed and developed and developing nations.developing nations.

Demographic TransitionDemographic Transition

The The demographic transitiondemographic transition is the general is the general pattern of demographic change from high birth pattern of demographic change from high birth and death rates to low birth and death rates.and death rates to low birth and death rates.

Industrial development causes economic and Industrial development causes economic and social progress that then affects population social progress that then affects population growth rates.growth rates.

Women and FertilityWomen and Fertility A decline in birth rates can most clearly be A decline in birth rates can most clearly be

related to increasing education and related to increasing education and economic independence for women.economic independence for women.

Educated women learn family planning Educated women learn family planning techniques and find that they do not need techniques and find that they do not need to bear as many children to ensure that to bear as many children to ensure that some will survive. some will survive.

Women are able to increase the Women are able to increase the prosperity for their families while spending prosperity for their families while spending less energy bearing and caring for less energy bearing and caring for children.children.