Exponential Population Growth

Exponential population growth is a model that describes the expansion of a population in an ideal, unlimited environment (Simon, Reece & Dickey, 2012, pg. 408). Since the year 1650, the human population has been undergoing the longest exponential growth of any large animal in history counting (Roser & Ortiz-Ospina, 2013). In 1650, there were about five hundred million people on the planet. By 1850, the population had doubled to one billion, and it doubled again just eighty years after that and then it doubled again just forty-five years after that. We are now well past seven billion and counting (Roser & Ortiz-Ospina, 2013).

A perennial problem in nature and in our lives is satisfying two competing impulses; quantity or quality (Albrecht, 2017)? In ecology, we size up who chooses quantity over quality by the R and K Selection Theory. The R and K Selection says that some organisms will reproduce in a way that aims for huge exponential growth, while others are just content to hit the maximum population size that their particular environment can sustain, which is also called the carrying capacity, and then stay at that level (Simon, Reece & Dickey, 2012, pg. 409).

Species that reproduce in a way that leads to a very fast growth are called R Selected Species. R is the maximum growth rate of a population and R Selected animals create a lot of offspring in their lifetime without too much concern for the wellbeing of each and every one of them. If some of the offspring gets eaten or dies off, then it's not that big of a deal because there are a multitude of them (Rafferty, 2014). On the other hand, K Selected Species only makes a few offspring in their lifetime and they invest in those offspring's very heavily. K is the carrying capacity of a population and K Selected Species usually end up living at population densities closer to their carrying capacity than R Selected ones (Rafferty, 2014).

However, things aren't so cut and dry in nature as most animals aren't very strongly K Selected or R Selected, it's more like a spectrum. Some organisms, usually smaller ones, reproduce more on the R Selected side and other organisms, usually larger ones, reproduce more on the K Selected side. Most species are somewhere in the middle. Although humans tend to reproduce more on the K Selected side of the spectrum, our population growth curve has been looking suspiciously like that of an R Selected Species. And exponential growth, even for R Selected Species, usually does not go on for three hundred and fifty years (Wall, & Przeworski, 2000). By eliminating a bunch of obstacles that would have made our numbers level off at a carrying capacity like diseases and predators, humans were able to figure out how to raise our carrying capacity so far indefinitely. These obstacles are called limiting factors and limiting factors are an environmental factor that restricts the number of individuals that can occupy a particular habitat, thus holding population growth in check (Simon, Reece & Dickey, 2012, pg. 409).

First, we have been able to increase our ability to feed ourselves. Humans rapid population growth started in Europe around the 17th century because that is when agriculture was becoming mechanized. New farming practices like domestication of animals and crops were increasing food production. From Europe, those agricultural practices and their accompanying population explosion spread to the New World and too much of the rest of the world by the mid-19th century (Kolankiewicz, 2016). Another thing that changed in the interest of human population came in the form of medical advances. Anton Van Leeuwenhoek, father of microbiology, was the first modern scientist to propose the germ theory of disease in 1700 and revolutionized human health, leading to things like vaccinations (Ramos, 2018). Now humans are no longer dying from things like the pelage or measles which meant that everyone lived longer, childhood survival rates improved as well as life expectancies, so the children grew up to have children themselves and grew to be very old.

In addition, we have been able to increase our ability to live comfortably in inhospitable places. Our great ancestors have been living in deserts and tundra for thousands of years but in the 20th century we expanded the human habitat to basically everywhere in the world. We have air conditioning to cool us in places where it can get very hot outside, warm clothes for when it can get very cold, airplanes to better increase traveling long distances safety, comfortably and in a way shorter amount of time, semi-trucks full of food that travel across the country and giant boat to take them overseas.

As our population grows, our carrying capacity grew right along with it. The human population does have a carrying capacity but we're not sure what it is. Back in 1679, it was Leeuwenhoek himself who was the first to publicly hazard a guess about the Earth's carrying capacity for humans guessing it to be around thirteen billion people (Ramos, 2018).. With all of those people we obviously need a lot of resources to survive like food, clean water, non-renewable resources like metals and fossil fuels. Everything that we consume requires space, whether it's space to grow or space to mine or produce or put our waste (Kolankiewicz, 2016). Ecologists make their estimates of how many people this planet can handle based on an ecological footprint, an estimate of the amount of land required to provide the resources, such as food, water, fuel, and housing, that an individual or a nation consumes and to absorb the waste it generates (Simon, Reece & Dickey, 2012, pg. 409). That footprint is very different depending on where you love and what your habits are.

Despite the fact that the earth is a very big place., space is a real limiting factor for us, and as our population grows, there will probably be more conflict over how our space is used. As humans take up more space, we also leave less space for other species, and as we use resources like trees and soil and clean water, that reduces the amount available to all kinds of other organisms. This is why biologists say that we are currently living though one of the biggest extinction events in recent geological history (Roser, 2013). The fact is, even though the human population continues to grow, the rate of population growth actually peaked around 1962 and has been declining ever since. At its peak, the human population was growing at about 2.2% per year, and these days, it's declined to about 1.1% and it's still falling (Roser, 2013). Back in the early 20th century, more of the world worked on farms, and maybe ate their own food. Kids were a real asset to a farm back then and they helped their parents run the farm, but that's not happening so much anymore. More and more people are living in cities where you don't need kids to help with the crops, so fewer people are having them because children cost a lot to raise, they are no longer bringing in money because we no longer need kids to work on the farm, and a lot of people have access to good birth control, so they don't have children.

Just because our population's growth rate is decreasing doesn't mean that humanity is going to stop anytime soon which is positive and negative on its own. In addition to reminding us that the rules of ecology apply to us just like any other organism, human population is important to think about because we definitely need to do something about it in my opinion. I'm not saying that we go all out and pull a 'Thanos' from 'Avengers; Infinity War' here, all I'm saying is that we're not going away but what will happen when everything else does go away?

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