for most of my life I've been told that the world is going to become overpopulated but recently I've noticed that the conversation around population growth has started to change the U.S fertility rate is actually shrinking and has been for a while it's been falling for the last almost 15 years now at this point I can't emphasize this enough there are not enough people if people don't have more children civilization is going to crumble mark my words but while some countries are concerned with a population bust there are still regions in the world that are experiencing a population boom according to the economist by 2050 Nigeria is forecasted to have 400 million people meaning it will overtake the United States as the world's third most populous country and as of today sub-Saharan Africa's population is growing at 2.7 percent a year which is more than twice as fast as South Asia which is at 1.2 percent and Latin America which is at point nine percent that means Africa is adding the population of France or Thailand every two years so which is is it is the global population crashing or is it exploding to answer this question we have to understand the demographic transition it's a model that has five different stages and it focuses on different economic and social developments of a society in the first stage societies have a high CBR and CDR which actually end up creating a low nir since the births and deaths end up canceling each other out Societies in this stage are traditionally lacking sanitation medicine contraceptive and have more of an agricultural based society in fact the majority of people work in subsistence agriculture which is when people produce food for themselves and not for sale you can see that during this stage migration is often focused around the search for food here people are just trying to meet their basic needs in fact the majority of human history actually took place during this stage but as of today there are no longer any countries that are in this stage of the demographic transition model now once the Industrial Revolution happened we started to see countries and societies transition into stage two of the demographic transition the Industrial Revolution led to the enclosure movement increased rates of urbanization allowed for more specialization in society increased society's food surplus and allowed for advancements to be made in medicine which would eventually lead to the medical Revolution Europe and North America were one of the first regions to enter stage two due to the diffusion of the Industrial Revolution eventually we saw Africa Asia and Latin America start to transition into stage two thanks to further diffusion of technology and due to the medical Revolution countries in stage two continue to have a high CBR but they start to see their CDR decrease which leads to a population boost as the CBR and CDR no longer cancel each other out during this stage societies increase their knowledge in medicine improve their agricultural production increase their food surplus and lower their IMR and CDR all of which leads to a population boom during this stage we also start to see increased rates of migration to urban areas this is due to people seeking more Economic Opportunity is in the city in the secondary sector of the economy and also due to the fact that many of the subsistence agricultural production is now shifting over into commercial agriculture besides people moving from rural areas to urban areas we may also see increased emigration as more migrants will seek economic opportunities in core countries or more developed countries today we can see that countries like Afghanistan are in stage two of the demographic transition model as seen here in their population pyramid notice that the majority of Afghanistan's population is in the pre-reproductive years and reproductive years which shows that the country has an expanding population eventually countries start to move into stage three during this stage the CBR starts to decrease along with the CDR continuing to decrease these changes in both the CBR and the CDR cause the nir now to become more modern as more people live in the cities they no longer have the space or the economic need for larger families medical advancements in society lead to a higher life expectancy and decrease the infant mortality rate which leads to families having less kids we may also start to see cultural changes in society as well such as how people view gender roles which may often lead to women gaining more rights in society and being allowed to participate more in the economy as Society starts to develop we start to see more and more jobs open up in the manufacturing sector which would be part of the secondary sector of the economy we also start to see more jobs starting to appear in the tertiary sector of the economy as well these new economic opportunities also shift migration patterns as well traditionally we see that less people emigrate from a country that has more jobs in the secondary and tertiary sector as the economy advances migrants will stay in their own country to be able to explore the economic opportunities that exist at home today we can look at Mexico as an example of a stage three country notice that when we're looking at Mexico's population pyramid the middle of the pyramid is starting to fill out more people in the country are now in their reproductive years and post-reproductive years we can see that Mexico is still growing as a country but not as fast as it would have been if it it was in stage two next is stage four which is defined by a low CBR and low CDR and actually now a low to Flat Nar here countries start to see more economic opportunities for all citizens higher rates of education for women more jobs in the tertiary sector of the economy and more intra-regional migration during the stage countries may experience zpg which is zero population growth this means that the country's CBR and CDR are essentially the same causing the nir to be zero this demographic shift occurs for a variety of different reasons we can see that economically more people are focused on their career and start to get married later in life which causes them to have children later as well which of course leads to smaller family sizes as the economy grows we will also see the cost of living increase which decreases the amount of disposable income that individuals have which will further decrease the TFR of a society as people start to feel like they can no longer afford to either start a family or support a larger culturally we start to see Society offer more education and opportunities for women during this stage which allow women to play a more active role in society and the economy this shift also allows women to pursue their own careers and goals instead of being seen as child Bear all these societal advancements help further decrease the society's CDR and IMR as people continue to gain more access to wealth they also gain access to Better Health Care Services and more nutritious foods which helps increase the average life expectancy and decrease the death rate today we can see that countries like the United States and China are good examples of a stage four country if we look at their population pyramids we can see that they form more of a box shape notice that the population spread out between the different age cohorts and while the countries are no longer seeing a large population boom they are also not seeing a large decline I do want to highlight that sometimes the country may move between stages due to political policy which can either promote people to have more children or deter people from having children government policies such as the one child policies are are what helped China transition into stage four but we'll talk about those policies more in our unit 2 topic 7 video lastly there's the speculative stage five which is defined by a negative nir hear a country's birth rate goes below the CDR causing the country's population to decrease countries that could be in stage five would be Japan or Germany notice how the majority of their population is located in the post-reproductive years on their population pyramids both of these countries have a negative nir which means their overall population is decreasing in order for a country to be growing they have to have a TFR above 2.1 this is known as the replacement rate if their TFR is below 2.1 the population will decrease over time remember though migration can change this and when we're talking about the CBR CDR and nir we are looking at births and deaths that take place in the country these indicators do not factor in Immigration or emigration okay so that's the demographic transition model next we have to go over the epidemiologic transition model but before we do don't forget to hit that subscribe button if you're finding value in this video and if you need some more help with your AP Human Geography studies check out my ultimate review packet and Discord server it's a great resource and it'll help you get an A in your class and a five on that National exam now the epidemiologic model goes along with the demographic transition model there are a couple differences but for the most part we can use this model to better understand the different causes of death for each stage of the demographic transition model stage one is defined by pestilence famine and death here people are going to die from a variety of different things parasitic diseases infectious diseases animal attacks pandemics epidemics food shortages dirty water you name it you can die to it one of the most well-known killers in this stage was actually the bubonic play now I mentioned epidemics and pandemics remember an epidemic is a disease that spreads through a region or community and a pandemic is a disease that spreads across multiple regions countries or possibly the world another term that you'll want to be familiar with is and which is a disease that stays in a particular area and does not spread through an entire region or Community now when countries transition from stage 1 to stage two we start to see a decrease in the amount of deaths caused by Major diseases this is due to a variety of different factors such as advancements in medicine an increase in food supply and a higher standard of living stage two is defined by less deaths and receding pandemic during stage two Society gains access to new technologies that not only improve the standard of living but also help increase the amount of food that is produced societies also start to eat more nutritious food and see improvements in sanitation as well remember during stage two is when the Industrial Revolution and medical Revolution occur these events decrease the country's CDR but like we talked about earlier in the video do not decrease the CBR right away which leads to societies to have a high nir as societies continue to advance they eventually enter stage three which is defined by degenerative diseases here people start to live longer and start to die from diseases which are human caused or caused by time for example heart attacks from eating unhealthy food or different types of cancer next to stage four which is defined by fighting degenerative diseases and longer life expectancy this is when medical advancements in society can delay degenerative diseases which increases a society's life expectancy during the stage most individuals will continue to improve their diets with more nutritious foods and make better health decisions like not choosing to use different drugs but at the same time we can see that these different advancements in society can also promote negative habits as well such as living a more sedentary lifestyle or eating more junk food which may lead to new health problems for individuals such as obesity or diabetes the last stage is stage five and it's defined by the re-emergence of infectious disease during this stage parasitic diseases and infectious diseases become more prevalent again this can happen for a variety of different reasons the first is the evolution of diseases this is when a society sees different diseases mutate and develop resistance to antibiotics we can see that over time as Society continues to use antibiotics we may see the development of superbugs which are different strains of bacteria or viruses that are resistant to most antibiotics the next reason is an increased rate of poverty and urbanization As Cities become larger and more densely populated it becomes easier for disease to spread throughout a city and when people live in poverty they are less likely to be able to afford different medication and health care services which can lead to an increase in the CDR lastly there is globalization when people travel around the world they gain experiences share ideas but also at the same time they share germs This Global Travel and connectivity can lead to pandemics such as covid-19 we saw that cities that had large international airports and densely populated areas saw covid-19 spread through their communities first we also saw people who were in lower income brackets had higher rates of covet since they had less access to health care services and were more likely to be working in jobs where it was more more likely to be exposed to the virus now both the demographic transition model and epidemiologic transition model are important models for this class so you'll want to make sure that you're familiar with both of them all right now you know the drill now comes the time to practice what we have learned answer the questions on the screen and when you're done head on down to the comments section below or the description of this video to check your answers and if you feel like you need some more practice with these models head over to my ultimate review packet for more help with not only just these models but everything else AP Human Geography related as always thank you so much for watching I'm Mr sin and I will see you geographers next time online