Demography is the study of human populations, including their size, structure and movements over time. Observable occurrences in demography are referred to as Phenomena.

Fertility is the ability of a population to produce offspring. Mortality is the frequency of deaths in a population. The Birth Rate of a population describes how many offspring are produced by each woman. A birth rate of 2 is the replacement fertility, assuming the mortality rate is constant and net migration is zero. This is where the population will exactly replace itself. A birth rate above this will cause the population to grow and a birth rate below this will cause the population to shrink. A Birth Rate Decline is driven by many factors including education, social attitudes, contraceptive availability, rising living costs and women working. When the birth rate declines (or life expectancy increases) an Ageing Population occurs. This is also known as demographic ageing and population ageing. An ageing population can lead to social exclusion, health issues, rising healthcare costs, economic slowdown, as well as more time with loved ones and cost savings. Life Expectancy is the period of time that a person can expect to live. This is increased by improved lifestyle and healthcare. Marriage is the legal or formal union of two individuals as partners in a personal relationship.

A Population Pyramid shows the structure of a population by age and gender. There are three main shapes of population pyramid:

• Expansive: This is an underdeveloped country with a high death rate and a high birth rate. The life expectancy is short, with a youthful population. This is a triangular shaped pyramid.

  

• Stationary: This is a developing country with a declining birth rate and a high but declining death rate. The life expectancy is increasing and there is an adult population. This is a bell-shaped pyramid.

  

• Contractive: This is a developed country with a low birth rate and a low death rate. The life expectancy is long with an ageing population. This is a bulb shaped pyramid.

  

Migration is the movement of people from one place to another with intentions of settling. Migration is influenced by push factors and pull factors. These can give individuals reason to relocate. Examples of push factors that may drive people to migrate away from a region are: low wages, poor working conditions, poverty, poor infrastructure, persecution, and unemployment. Examples of pull factors that may cause people to migrate to a region are: good healthcare and education, high wages, good working conditions, high standard of living, food security, and wellbeing. There are many types of migrants:

• An Asylum Seeker is an individual awaiting sanctuary processing due to fear of persecution.

• A Refugee is a person fleeing a country due to persecution, war or violence.

• An Immigrant is someone who is moving permanently to another country.

• An Illegal Migrant is someone who is residing in a country without legal permission.

• Political Migrants are individuals moving due to political reasons such as persecution.

• Economic Migrants are workers seeking economic opportunities (such as higher wages) in another country.

• Environmental Migrants are individuals forced to migrate due to adverse local environmental changes or natural disasters.

• Labour Migrants are people who move for employment purposes within a country.

Internal Migration is movement within a country from one area to another, while International Migration involves crossing borders for relocation. Urbanisation refers to the growth of urban area in relation to rural areas. This can be from higher population growth in urban areas, or from migration from rural to urban areas. A lack of Inward Migration raises the average age of a population, as less young people are moving in. Immigration to a country in violation of its immigration laws is Illegal Immigration. Forced Migration (also called displacement) is compelled movement due to conflict, violence or disasters. Human Trafficking and Modern Slavery are the illegal movement and exploitation of individuals for labour or services.

Social Mobility describes the movement of individuals, families or groups within or between social strata. There are a number of types of social mobility:

• Horizontal mobility: Where a person changes occupation but does not change their social standing, movement within a social standing. For example, a person may move from working as a doctor to teaching in a medical school.

• Vertical mobility: Where a person’s social standing changes due to a change in their occupation, religious or political beliefs, or education. This can be ascending (in social status), for example being promoted to a managerial position in a job. Alternatively this can be descending, for example a business owner declaring bankruptcy.

• Intergenerational mobility: Where a generation is higher in social status than the previous generation. For example, parents with a high school education may raise children who get tertiary qualifications.

• Intragenerational mobility: Where a person rises in social standing within their lifetime. For example, a person may climb the corporate ladder over their working life.

A number of factors interact with social mobility:

• Health: Inequalities in healthcare may relate to the social standing of a person (ie. People of lower socioeconomic class may receive worse healthcare than people of higher socioeconomic class). People who are healthy may also be more productive.

• Education: One tool for rising in social standing is to become more educated. Greater disparity between education available to different social classes leads to lower upward social mobility of lower class people. Furthermore, people with a higher social standing may be able to provide better education to their children.

• Housing: Mixed housing is a concept that states that by mixing neighbourhoods with households of different social classes, upward social mobility may be encouraged. This can be due to safer living conditions, positive behavioural changes, access to better healthcare and education, and improved infrastructure, as people of higher socioeconomic class may demand these. However, it is also possible that gentrification may occur. People of higher socioeconomic class may keep to themselves, and people of lower socioeconomic class are left behind.

• Income: High levels of economic mobility lead to low levels of social mobility. A large income disparity between middle and lower classes can cause ‘Economic Despair’, whereby people no longer see value in upward mobility. This may cause them to stop investing in their own education and healthcare.

• Race: Racial inequality stems from colonialism. Today, it is less prevalent. However, more frequency policing of minority groups can cause them to have less upward social mobility, as they may be fired from their job, are be less likely to receive promotions.

• Gender: Gender inequality means that women have less upward social mobility than men. This is due to less investment in women’s education and underemployment. This is cultural in many countries, where women leave breadwinning to the man and either do not work, or work in a job they are overqualified for. When women take a career break to have children, they have many years of lost income and work experience, which can also result in underemployment.

A rapid increase in population size is called a Population Explosion. When a high human population begins to cause environmental deterioration or quality of life issues, it is referred to as Overpopulation.

The Malthusian Theory of Population states that population growth is exponential, while growth of the food supply is arithmetic. This means that a growing population will eventually run out of food. Checks on the population will prevent this from happening. Positive checks can include events such as war, famine, epidemics, or natural disasters. Preventative checks include later marriage, contraceptives, or living a simpler lifestyle. These not only prevent consumption of the food supply, they also prevent environmental damage from overpopulation.

When environmental deterioration leads to the disappearance of animal species, this is Extinction. Climate Change refers to long-term alternation of temperature and weather patterns in a region. Overpopulation can cause both extinction of plant and animal species and climate change. An increase in the overall temperature of the Earth’s atmosphere is Global Warming.

Urban Congestion refers of overcrowding and traffic congestion in urban (city) areas. Wellbeing refers to positive intangible aspects of life such as happiness, trust and biodiversity. Food Security refers to physical and economic access to sufficient safe and nutritious food to sustain a healthy life. Territorial Conflict is a dispute over territory, often leading to armed conflict. Unemployment is the state of being without work, yet actively seeking employment.

A period where mortality and fertility rates decline in a region is called a Demographic Transition. Demographic transitions have five stages:

1. Stage one is pre-industrial society. Birth rates and death rates are high and roughly in balance. Population growth is typically very slow, as society is constrained by the food supply.

2. Stage two is a developing society. Improvements in food supply and sanitation (due to technological advancement) lead to a drop in death rates. The life expectancy increases and disease reduces. This leads to a youthful population.

3. Stage three is a further developing society. Birth rates fall due to factors including contraception, changes in values, higher wages, less reliance on subsistence agriculture, a reduction in child labourers, and increase in education (particularly for women). Population growth begins to level off.

4. Stage four is a developed society. Birth and death rates are low, and may drop below replacement level. The population in ageing and may begin to shrink. As the population born during stage two ages, an economic burden is placed on the working population.

5. Stage five has not yet been seen, but could see more below-replacement fertility rates, or an increase in fertility to maintain population levels.