Introduction to Human Population and Quick Overview of Human Population History

The human population is comparable to thriving bacteria, multiplying steadily over time until it completely takes over the host body and can possibly lead to unfortunate consequences. The human population is a forever growing group most people do not give a second thought about, but is in fact reaching a very precarious position in terms of the scary pace at which it continues to grow. Our effects on the earth are undeniable and the future consequences inevitable as humans blindly reproduce. Yet, how did we reach this situation? What are the major factors that have contributed to the decline and eventual growth of the human population through the years? And what does the future hold in relation to the effect of the human population? This blog will attempt a broad overview to answer these questions.

            In order to understand the effects the human population currently has, we must start from the beginning and comprehend how humans first came about. While there is not one theory agreed on as the origin of mankind, a leading theory introduced the concept of the ‘recent African origin’ model. This model discusses the idea that the ancestors of all modern humans originated in East Africa. It is estimated around 100,000 years ago, humans left the continent of Africa and migrated to other parts of the world, displacing previously established humans species such as Neanderthals in Europe (Prugnolle et al 2005). The human population grew at a steady pace. Up until the eleventh millennium B.C., it is estimated that the world population stabilized at about one million people whose main methods of survival consisted of hunting and gathering which ensured a low population density. The total world population never exceeded fifteen million inhabitants until the invention and revolution of agriculture. Fast forward to about 2,000 years ago around the dawn of the first millennium A.D., the world’s population was around 300 million people. About 1,000 years later, the population had risen by around ten million. Growth was stunted for a period of time due to different plagues. But by the time of the Industrial Revolution in the late 18^th century, the population exploded. 800 years later the population had reached a milestone of one billion people. A little over one hundred years later, the population reached two billion. Growth increased dramatically since then. It is now estimated that the world holds over seven billion people (see figure 1) (Lewis 2004).

Figure 1: Map of  world population distribution

            The growth of the human population did not happen by a miracle overnight. There were several forces and factors that came into play concerning the human population throughout history. While these forces and factors are still debated about today, they can arguably be summarized into four different areas: geographical location, natural resources, disease, and technology. The development of each area throughout history will be presented as well as an in depth analysis of how it has affected the human population in the past, present, and future in relation to natality, mortality, emigration, immigration, and fecundity.

Geographial Location

            One of the key factors when it comes to the growth of the human population is the geographical location of societies. Different geographical locations encompass different forces such as climate or, in a societal context, different cultural norms in relation to population.

            Climate is the characteristic condition of the atmosphere near the earth’s certain at a certain place on the earth. When referring to climate, it usual means the long term weather conditions at that location (predictable weather occurring for at least thirty years). Climate also includes the region’s general pattern of weather conditions, seasons and weather extremes. Climate zones can be broken up into five different areas: tropical, dry, temperate, cold, and polar. The locations of these areas are determined by where the area resides in relation to the equator and how cold and hot air interacts.

            Dry climates are found near the equator or approximately between eighteen degrees and twenty-eight degrees in both hemispheres. These areas are just north and south of the equator. These climates are characterized by light winds, which allows for the evaporation of moisture in the heat. Air generally flows downward so the dry climates rarely experience rainfall therefore annual rainfall is very low. Due to the intense heat, it is rare to find human societies that exist for a long period of time in these areas. From early on in history, humans avoid dry climates such as deserts because the amount of usable natural resources is very low. These dry climates do not have rainfall making it hard to grow agriculture, and these areas are not located near sources of water. Due to the low biodiversity of fauna and flora, humans have not and will not settle in dry climates, making the population in these areas very low (Prugnolle et al 2005).

            Tropical climates are usually found in the latitude range of ten degrees south to twenty-five degrees north. These areas are characterized by heavy rainfall throughout the year. The total annual rainfall is often more one hundred inches. While these areas do experience seasonal differences that affect monthly rainfall, the temperature usually stays around the low eighty degrees, with humidity around eighty percent. Tropical climates support human population growth more than dry climates but not much more. The climate is on one of the extreme ends of weather. Instead of unusually hot weather, the weather is wet. It makes it hard for large groups of people to live in a place where it is very moist, warm, with a lot of rainfall. Specialized groups of humans live in tropical areas such as the Pygmy Tribe. Many of these societies that live within rainforests and tropical zones resemble humans from early times following a more hunter-gather model. Thus, like early humans, the population is mostly stable here. The way in which these societies live, do not support a very large population so growth is not usually seen in these areas (Prugnolle et al 2005).  

            Temperate climates and located between the tropics and the polar regions. While these regions do experience temperature changes in different seasons, the temperature stays mostly moderate instead of experiencing extreme cold or hot weather. However there are a few areas which can experience extreme temperature changes during different seasons because they are not located near the sea which helps in temperature regulation. A vast majority of the human population lives in temperate regions. One reason humans prefer temperate climates are because they do not experience extreme temperatures as often. The climate stays mostly neutral and thus makes it easier to live in. Additionally the areas that experience temperate climates end up dominating a lot of land mass and thus naturally the more land mass the more humans end up living in those areas. Thus in the areas where temperature climates are experienced, mostly North America and Asia, there can be seen large growths of the human population (Strahler 1984).

            The last two climates are cold climates and polar climates. As suggested by their names, both of these regions support cold to freezing weather. They are located closer to the poles. The further away from the equator, the colder the climate is. In the winter these areas are characterized by darkness twenty-four hours a day and the opposite in summer with sun twenty-four hours a day. Despite the amount of sunlight, there is a lack of warmth with polar climates resulting in treeless tundra, glaciers, or a permanent to semi permanent layer of ice. The extreme temperatures along with the lack of land to use for agriculture, rarely sustain human life (McKnight 2000).

Figure 2: Map of climate distribution

 

            In the beginning, there was a relatively even distribution of humans as they began to migrate to other continents, yet certain geographical locations experienced high growth and others did not. While it can be easily assumed places such as the polar regions did not experience a human population growth because of the extreme temperatures, other factors in addition to weather can dictate if a certain location will experience growth of the population. Areas that have access to natural resources such as bodies of water will experience more of a growth because the growth can be supported (an idea that will be researched later in this blog). But many of these areas have a ‘natural population control’ built into it through Mother Nature. The areas that support the most growth unfortunately are the areas that experience many natural disasters (Skidmore and Toya 2006). The United States, a country with roughly 315 million people, experience many natural disasters at each of the highest populated states (California, Texas, Florida, and New York) (World Fact Book). In California, earthquakes are a common occurrence because the state is located on the San Andreas Fault. Every year the state experiences many thousands of small earthquakes. The most notable earthquakes are the 1906 San Francisco earthquake which killed 3000 people, and more recently the 1989 Loma Prieta earthquake and the 1994 Northridge earthquake both of which caused widespread damage and deaths (USGS 2013). Texas due to its location and size experiences many natural disasters such as earthquakes, hurricanes, tornadoes, and wildfires. Florida has experienced about 488 tropical or subtropical cyclones with a collective death toll of 10,272 people (National Hurricane Center 2013). New York while it also has had its fair share of tornadoes and earthquakes, it is notable for the blizzards it experiences (NOAA 2013). However these numbers pale in comparison to other natural disasters around the world. China, the county with the largest population, has experienced some of the most crippling disasters. China is continually affected by floods, typhoons, and earthquakes. Death tolls can be from the hundreds of thousands up into the millions as with the 1931 China floods (Skidmore and Toya 2006). Although most of the natural disasters listed are on a larger scale, one must still take into account smaller disasters such as volcanic eruptions, heat waves or avalanches amongst other naturally occurring events. While experiencing natural disasters is not a huge indicator of population growth, it is a factor which affects mortality rates as well as immigration into the area by others. It is also a factor that does keep certain populations from becoming more over populated than the already are (Skidmore and Toya).

Figure 3: Table of top ten deadliest disasters of all time

 

            So far, in terms of geographical location, only natural factors such as climate and disaster have been taken into account in relation to effects on population growth, but there are several cultural differences that can also affect population depending on location. Human population control is the practice of artificially altering the rate of growth of a human population. In the past, human population control has been implemented usually through mandates issued by the government to limit the population birth rate. These mandates are a result of high levels of poverty, environmental concerns and religious reasons as a result of overpopulation (Whaley Eager 2004). Population in different regions has been a concern since ancient times. In 300 BC India, many political philosophers connected a large population with power. In ancient Greek, (427-322 BC) scholars such as Plato and Aristotle highlighted that the best population to have would be one that allowed for efficient administration and citizen participation but also had to be large enough in case they needed to defend the city against attacks. Confucius was also an advocated for human population control. He as well as other Chinese writers cautioned that excessive growth would lead to inefficiency per person, reduce the standards of living, and cause strife. Ancient Rome had a difference stance. Due to their need for manpower to conquer Europe, they encouraged and enacted laws to make couples marry early and have frequent childbirth. Couples who were childless and could not comply with the laws experienced higher taxes and unfair treatment. Despite means of controlling and regulating populations such as infanticide in early Rome, the population grew. By the time the Middle Ages rolled around, population was not a high priority. There were no repercussions if couples had children or did not. Therefore, when left to their own devices, humans continued to procreate. From the middle ages into the 16^th and 17^th centuries, the population boomed in Europe and Asia. It was finally in the 20^th century, countries with overpopulation began to realize they needed to slow down growth (Whaley Eager 2004). There are several different current day practices when it comes to population control. In China there is a one-child policy where having more than one child per family is discouraged. Unauthorized births can be punished through fines and there are extreme cases where families are allegedly forced to be sterilized or perform abortions. The policy first began in 1978 and has supposedly helped prevent 400 million births. In India, those with two or less children area allowed to run for elections. In Iran, couples must go through required contraceptive courses before they can obtain a marriage license. In the United States, the first human population control was enacted with Title X in 1970. This allowed for public access to contraceptive services, supplies, and information. The support for population control has since increased. With healthcare being made mandatory for all, now all people have access to contraceptives and information, in particular women have much easier access to abortion clinics which are either free or inexpensive (Knudsen 2006).

            In summary, geographical location can definitely affect the population. The basic climate of a location can dictate if it can easily support humans and their growth. The population has natural controls such as natural disasters, but there are also cultural controls. While in the past populations were usually allowed to grow with no consequences, many countries now acknowledge the downsides to overpopulation and use government mandates to control population.

Natural Resources

            Life would not be able to be supported without the use of natural resources. There are four natural resources most used by the 7 billion people on the planet: water, fossil fuels, wood, and phosphorus.

             Water is a vital resource and is needed for all aspects of human and ecosystem survival. There is no way around using water. It cannot be replaced as a resource. In the past water was only obtained through natural lakes, streams, and other supplies already in existence. It was not until the Neolithic that man first dug permanent water wells. The size of the population was already dictated by the size of the local water supply. With the creation of the well, human settlements could begin to grow proportional to the size of the well. Along the same lines of the well, man also learned to create a separate receptacle for human waste. Until that creation, there was contamination from feces into the clean water supply. From there, access to water became easier as other inventions allowed delivery of water to buildings as well as purifying processes so even contaminated water could be used (Linton 2010). Not only is water itself a necessary resource for humans to function and for populations to grow, but also areas that had access to natural oceans could sustain a much larger human population. Oceans provide food in form of fish. It is used for transportation, mined for minerals, and drilled for crude oil. The oceans also play a critical role in removing carbon from the atmosphere and providing oxygen in addition to regulation of temperatures (Ardus and Champ 1990). It is easy to infer from all of these uses that the human population would naturally grow in locations closer to oceans. Using information from the previous geographical location section, it can be assumed countries in temperate climates with access to a large body of water can support a large population which is proven true with countries such as the United States and China.

          Fossil fuels are formed by natural processes such as the decomposition of buried dead organisms. It is a process that takes millions of years but produce things such as coal, petroleum, and natural gases. An important characteristic of fossil fuels are that they are non-renewable because they take a very long time to form. Fossil fuels are formed mostly from the carbon rich remains of ancient plankton after exposure to heat and pressure in the Earth’s crust over hundreds of millions of years. Over time, the residue is covered by layers of mud and silt and therefore is further down in the Earth’s crust. Around the mid1800’s the first oil refineries were built (Rise of Standard Oil Video) to begin to process fossil fuels. These refineries were not very popular because the demand for refined fuel was limited. The first commercial oil well in Canada began shortly thereafter. 1.5 million liters of crude oil was extracted with two years and much of it being refined to put into kerosene lamps. The fossil fuel industry began to gain momentum as people began to realize the ease and availability of extracting oil from the land compared to harvesting oil from other resources such as whales. (Coleman 1996). As the World Wars occurred and after the Second World War, oil became a main import and export. The Middle East took the lead over the United States in oil production. Oil is currently one of the most used resources in the world used to fuel factories, cars, and much more.  In relation to human populations, the use of fossil fuels makes living easier. Oil can be used in transportation, providing energy in the beginning for industry needs like pumping water to fire steam engines, and now generating electricity amongst other uses. Oil simplified many things, making the process of providing resources to the general population easier which thus helped support the population as it grew. The use of fossil fuels encouraged population growth.

Figure 4: A graph of the use of different fossil fuels

 

          Another natural resource which plays a role in population growth is wood. Because wood has been so readily available through the myriad of forests, it was the first resource taken advantage of in history. Around the time of 2300 to 2030 BCE, the conifer forests of Mount Lebanon provided timber in order to complete shipbuilding, railways, large building construction, and many other uses such as forms of payment (Mikesell 1969). It was an ideal substance because of the durability of the material. But, due to the lack of other resources it was only a matter of time until deforestation began in mass production. Some of the earlier accounts of deforestation are from forests in the Middle East near the Fertile Crescent in addition to stories gathered from “The Epic of Gilgamesh” (Mikesell 1969). Thus it is easily inferred that those who had access to forests therefore held the power. While previously people in the Middle East had power, by the time 2000 BCE came, most of the major forests were depleted. Demand shifted to the Mediterranean because the Greek had timber. Wood, around this time, was used for fuel in copper furnaces in order to produce bronze and thus became the major export. Power shifted from Crete, to Greece, to Macedonia, and to Asia Minor in succession as the country before it ran out of wood (Oosthoek Video). Europe because was the leading continent in deforestation. In the 15^th and 16^th centuries, there was an even larger increase in the demand for wood because sturdy ships were needed to conduct trade and travel throughout the world (Mikesell 1969). Wood allowed for the growth of the populations because of its usage. It allowed for ships to be made in order to conquer new lands and conduct trade. Wood allowed for buildings to become greater to house more people. Wood was used a fuel to help cook food and keep places warm. The use of wood allowed for basic survival, but the application of the uses of wood encouraged growth of the human population.

          Phosphorus is another vital resource in the growth of human populations. Phosphorus is a nonmetallic chemical element. As a mineral, it is almost always present as inorganic phosphate rocks. Phosphorus was first discovered in 1669 by Hennig Brand. In the beginning, the element was first use in explosives, poisons, and nerve agents. It has gone through many uses and experiments. But phosphorus became important during the 19^th century when world phosphate production turned to the mining of tropical island deposits formed from bird and bat guano. The dominant application of phosphorus is now in fertilizer. The element is extremely essential for plant nutrients. In order for the population to grow, there needed to be a food supply to allow the growth. While the oceans were providing some food and the crops producing a subsistent living, the population was growing and needed stronger support from the agricultural side to sustain the growth. With the application of phosphorus in the 20^th century, crops thrived. The harvests were becoming bigger. Additionally, more land was able to be used for agriculture because despite the natural conditions of the soil, if fertilizer was added containing phosphorus, then crops could survive (Emsley 2002). This is in direct contrast to early hunters and gathers. The crops sustaining that model of living were barely enough. A lot of individuals ended up having a low caloric intake which led to low body fat and fertility at an advanced age. By advancing the nutrients of the crops and the amount of crops, the human population benefit outweighs the costs of harvest and thus is able to grow (Strong Lecture 4/16/13).

          Water, fossil fuels, wood, and phosphorus all aided the world population growth. Access to more of the resources or better quality versions of the resources meant the population could grow without hesitation. We are now reaching a time when a lot of these resources are harder to access and require more energy to harvest. Yet, population growth has gained a momentum that is hard to stop. So will the resources run out and force a cap on the population or will the population make the drastic change to place a cap on themselves and save resources?

Disease

           Other than natural disasters, diseases are the most known entities to cause mass death in the human population. Disease is an abnormal condition that affects the body of an organism. It is often considered a medical condition with each disease having its own specific symptoms and signs. Diseases can be caused by many things such as external sources, other infected people, or internal sources due to hereditary predispositions. There are four main types of disease: pathogenic disease, deficiency disease, hereditary disease, and physiological disease (Johnson 2002). A pathogen is an infectious agent (germ) that can cause disease in a host body. The host can be any plant, animal, human, or other microorganisms. Examples of pathogenic diseases are smallpox, influenza, chickenpox, and measles. Deficiency disease (nutritional disease) is a disease in humans that can be directly or indirectly caused by missing essential nutrients in the everyday diet. This disease is known for causing two extreme reactions, obesity and malnutrition. Hereditary disease is a genetic disorder. It can be caused by mutations and abnormalities in the genome. This disease is also characterized as a lifelong disease because it is usually present in the child from birth. These diseases are also heritable and can be passed down from generation to generation. An example of this disease is certain forms of cancer. A physiological disease is what the normal regulation of the body’s system is affected. This can result from certain organs in the body not working properly or if certain cellular structures change over time, it can cause illness. An example of a physiological disease is asthma or diabetes.

The top ten deadliest epidemics of all time are categorized by one of the four groups listed and has had extremely negative consequences on the human population. The biggest worldwide epidemic was smallpox. Smallpox is an extremely infectious pathogenic disease. Smallpox was characterized by a rash and after fluid-filled blisters which can cause blindness, scarring, limb deformities, and in many cases, death (Barquet and Domingo 1997). Smallpox is believed to have first been found in the mummified remains of Ramses V who died over 3000 years ago. Through trading routes between Egypt and India, it is believed that the disease spread and from there was introduced to China and then Japan. It is unclear how it began to spread to the rest of the world, but by the time of the Middle Ages, the population increased and around the 16^th century smallpox was well established throughout many regions in Europe. Smallpox continued to ravage the world and by the mid-18^th century it was a major endemic disease everywhere but Australia. In Europe during the 18^th century it was the leading cause of death killing at least 400,000 people per year. Death was rampant until the use of vaccinations. Through the push of the governments, and donations of vaccines to poorer countries, smallpox was finally eradicated in 1979. Smallpox was to blame for 300 to 500 million deaths during the 20^th century and at the height, about 15 million people contracted the disease per year and about 2 million of them died. Overall, smallpox was definitely a disease, during its height that affected the growth of the human population. It put natural holds on growth until its eradication and then once again the population began to grow (Barquet and Domingo 1997).

The second largest epidemic of all time was the measles. The measles is also a pathogenic disease which infects the respiratory system. Symptoms of the measles include fever, cough, running nose, red eyes, and rashes. Measles are also highly contagious and can by caught through transmission of respiratory fluids (Broy et al 2009). While the measles today are rarely fatal, it was not the same case throughout history. The first known case of the measles was known as the Plague of Galen around 165-180 AD. It killed one third of the population in certain areas and is the cause for extreme loss in the Roman army. In 1529, an outbreak of the disease in Cuba killed two-thirds of the native people there after they already survived a smallpox outbreak. From there it continued to ravage Honduras, Mexico, Central America, and the Incas. In the last 150 years alone, measles has been thought to have killed about 200 million people around the world. It has been extremely hard to eradicate measles completely because to date, 21 strains exist and can at any time produce more strains. While vaccines have definitely improved the mortality rate of those who contract measles, there are still outbreaks today. One of the most recent large outbreaks happened in Japan in 2007, in Bulgaria in 2009, and as recent as March of 2013 with over 1000 cases and one death. While death is not common last stage for the measles anymore, it still can produce some fatalities. There is no denying that measles definitely affected population growth (Broy et al 2009).

The third largest epidemic was the Black Death. While it does not have any recent cases in the past couple centuries, the centuries that it was present, were devastating. The Black Death is a pathogen from bacteria that caused several forms of the plague. Symptoms of the disease were pustules formed in the groin, neck, and armpits which oozed pus and bled when opened. Other signs included spots, rashes, fever, and vomiting, but most of the time, death was certain from two to seven days after contraction. The Black Death had origins either in or nearby China. It spread to other parts of the world either through the Silk Road trade route or by ships (Herlihy 1997). There have been three major outbreaks of the plague. The first was the Plague of Justinian around the 6^th and the 7^th centuries. This outbreak is the first known attack of the Black Death as well as the first patterns of the bubonic plague. During this outbreak, almost forty percent of the population of Constantinople died from the plague. The plague continued till it wiped out about half of Europe’s population and then declined. The plague was not seen again in Europe until the Black Death in the 14^th century. Here the plague reached its peak. It had a drastic affect on the European population, decimating huge numbers of people. The plague had caused rampant death, despair, and persecution of minorities as scapegoats for the introduction of the plague into society. In the 14^th century alone, it is estimated that the Black Death reduced the world population from 450 million to 350 million. The third pandemic hit China around the late 1800’s and also affected India, but the plague stayed within the confines of the West. Since the last outbreak, there has only been limited number of cases in the past century. Overall the plague has killed over 100 million people within a small time period and is one of the more violent epidemics which have affected the world population (Herlihy 1997).

While all of the top ten epidemics have caused countless of deaths on the world population throughout history, there are a handful that still cause death today. In addition to small outbreaks of the measles, malaria, tuberculosis, and AIDS still wreak havoc in society today. Malaria is a mosquito borne infectious disease. It begins with a bite from a mosquito and the saliva of the infected insect travels through your blood. Malaria causes symptoms that typically include fever, headache, and can progress to a coma or death. The disease is widespread in certain tropical regions including many areas around the equator because the conditions prove to be a perfect breeding habitat for mosquitoes. In 2010 alone, there had been an estimated 219 million documented cases and around 1.2 million deaths from the disease. In total, there is an upwards of 80 million deaths from malaria. Currently there are no effective vaccines that exist for malaria although there is research being conducted to create one. There are other defenses against malaria such as antimalarial drugs, but countries without access to these drugs and with no vaccinations, malaria will continue to be a deadly epidemic (Sarkar et al 2009). Tuberculosis is a common and lethal infectious disease caused by different strains of the bacteria, Mycobacterium tuberculosis. Tuberculosis is characterized by attacking mainly the lungs and can also spread to other parts of the body. It can spread through the air and be transmitted from person to person. The symptoms of tuberculosis are coughing, fever, night sweats, and weight loss. It is believed that about one third of the world’s population was infected with tuberculosis with new infections happening at a rate of about one per second. Every year there are millions of cases of tuberculosis. In 2010, 8.8 million cases were reported and about 1.5 million deaths as a result either directly or indirectly from tuberculosis. Currently, under developed countries still have many cases of tuberculosis because of compromised and weak immune systems after contracting HIV and AIDS. There have been between 40 to 100 million deaths from tuberculosis (Lawn and Zumla 2011). The last of the major epidemics currently in existence is AIDS.  AIDS is a disease of the human immune systems caused by an infection of human immunodeficiency virus (HIV). With the initial contraction of HIV, there are influenza-like symptoms. After, there can be long periods without any symptoms at all while the virus slowly attacks the immune system.  The last stage of HIV is considered to be AIDS. HIV is transmitted through unprotected sexual intercourse and exchange of bodily fluids. Because HIV/AIDS attacks the immune system, a person is much more likely to be affected by other diseases and sicknesses because the body cannot fight against it. Since the discovery of AIDS, it has caused about 30 millions deaths as of 2009 and as of 2010, it is estimated that 34 million people are living with it around the world. There are no cures or vaccines as of now, but there are ways to slow the course of the disease (Baggaley et al 2006). 

Figure 5: Table of the top ten deadliest epidemics

           Disease, in the past and in the present, has affected populations. Disease alone is responsible for killing over a billion people in the world. It has wreaked havoc on population in the history through means such as small pox or the Black Death, and currently affects our population through AIDS, malaria, and tuberculosis. It is hard to infer if these diseases will become worse with time, or if new diseases will be formed, but disease is definitely a huge factor affecting the world population.