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Human population growth

Hank explores human population growth, exponential growth of populations, and R- and K-strategists. Created by EcoGeek.

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  • spunky sam blue style avatar for user Paul Kang
    Hank says that sewage systems were first around in Europe around 1500, but weren't much better systems around since antiquity?
    (16 votes)
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    • leaf blue style avatar for user Peterson
      Yes, the Roman Empire had a complex sanitation system, the exact techniques of which are believed to have been lost during the Dark Ages. Even older than Rome, though, are the sanitation systems of certain Indus Valley civilization cities, such as Harappa, which had sewage and waste drainage structures that were built with bricks, and connected to outdoor toilets. Minoan cities also possessed similar setups. Perhaps what Hank is referring to is that modern sewage systems were first developed during the 1500s, although from my research, most European cities did not have functioning systems until the Industrial era.
      (30 votes)
  • spunky sam blue style avatar for user Naimish
    at hank says 'juggernaut'.what does that mean?
    did i get the spelling right?
    (8 votes)
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  • aqualine ultimate style avatar for user Padmavathy Thangapandian
    Before few thousands of years ago how many years was the average amount of a human life?
    (3 votes)
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    • piceratops ultimate style avatar for user Just Keith
      We don't have sufficient records to be sure, but estimates vary between 20 and 30 years. But that includes children who died at an early age. If someone reached adulthood, they would reasonably expect to live to be 45-50 years old. But there is a wide variation in that number, depending on who does the estimates and what part of the planet the people lived in (some were more disease-prone than others, some where more famine-prone than others).
      (3 votes)
  • starky ultimate style avatar for user Vee T
    What would the human population be in 2080?
    (3 votes)
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  • leafers ultimate style avatar for user RJ
    Did Europe really see rapid population growth before parts of Asia, as he says at ? And how is historical population calculated?
    (3 votes)
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    • old spice man green style avatar for user Matt B
      The more resources a nation had the more it could provide for its offspring. Sometime in the 18th century there was the industrial revolution and people become more optimistic. Europe felt the industrial revolution before Asia did, and so population growth was greater in Europe.

      Industrial Revolution > greater productivity > more wealth generated > more payoff > better standard of living > better means of taking care of children > smaller child mortality > greater population growth
      (1 vote)
  • starky ultimate style avatar for user Arpit Jain
    Considering too many people is a problem because of food/space/etc, what is the best way someone can help offset these issues?
    (3 votes)
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    • piceratops ultimate style avatar for user Shriya
      Education is the first solution. People need to educated on the consequences that their actions have on the earth, they need to be educated on birth control and family planning, and finding alternate solutions for energy sources.
      You would find that in many developing countries ( countries in Africa, South America and Asia - excluding Japan), the population is increasing at an alarming rate! This is a result due to the unavailability of birth control and family planning. This means that more space is being used and their is a greater demand for resources. This is incredibly unsustainable!
      People should be eating healthier, it might sound strange but the food that you eat has a huge impact on the environment. In Brazil, multiple football field sized areas of trees are being removed to accommodate cattle herds since beef is in such a high demand. The first step toward sustainable living is to partake in meat free Mondays. Other than using up a lot of space, cattle negatively affect the environment by releasing methane gas that contributes to global warming and using up natural resources. If not carefully controlled, cattle will feed on grass until it is too short to recover. This leads to other environmental problems like soil erosion.
      I hope that this helps!
      (4 votes)
  • blobby green style avatar for user delvondogg
    Do all animals need water to survive?
    (0 votes)
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  • aqualine ultimate style avatar for user Tanisha Chincholkar
    What is the link between growing population and environmental degradation ?
    (1 vote)
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    • leaf red style avatar for user manviudupa
      when there is growing population the there is increased use of everything . which means increased use of land,water food etc and there is deforestation because they need land to build houses industries etc.even people buy more vehicles etc which pollute the environment.therefore ,in turn leads to environmental degradation.
      (2 votes)
  • ohnoes default style avatar for user Aqua
    What would happen if the humans managed to, against all odds, get rid of all our limiting factors. Would the carrying capacity become infinite? or is there some invisible firewall I'm not seeing?
    (1 vote)
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    • duskpin ultimate style avatar for user Laurent
      In a world where there is an infinite supply of resources, nearly no metabolic wastes produced and where all organisms were fertile as well as having no mutations for any detrimental traits, this would be may be possible, but obviously very highly unlikely in our world.
      (2 votes)
  • primosaur ultimate style avatar for user Paul Spexarth
    at he is talking about carrying capacity (K-) why do they use K- instead of C-
    wouldn't that be easier?
    (1 vote)
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Video transcript

- If being alive on Earth was some kind of contest, humans, I think, would win it hands down. As population of organisms, we're the Michael Phelps of being alive, only we have 250,000 times more gold medals. Last week, we talked about exponential growth, when a population grows at a rate proportional to the size of the population, even as that size of the population keeps increasing. Well, since around the year 1650, the human population has been undergoing probably the longest period of exponential growth of any large animal in history ever. In 1650, there were about 500 million people on the planet. By 1850, the population had doubled to one billion, and it doubled again just 80 years after that and doubled again just 45 years after that. We are now well past seven billion and counting. So think about this. Today, there are 80-year-olds who have watched the population of their species on Earth triple. So why is this happening? And how? And how long can it go on because it's kind of uncomfortable? Let's say you're shopping for dinner. And bear with me, we're going to relate it back to ecology in a second. But you got a lot of choices at your grocery store. You could buy five packs of ramen for a dollar, or you could buy some fancy ravioli made by Italian nuns out of organic pasta for like $20 a pound. They're both noodles, they're both food, but with the ramen, you get more whereas with the handmade stuff, it tastes better, higher quality. Well, what do you do? It's a perennial problem in nature and in our lives, satisfying the two competing impulses, do I have more or do I have the best. Quantity or quality, tough choice. Although we're not really aware of it, all organisms make a similar choice through how they reproduce. In ecology, we size up who chooses quantity over quality by something called the R versus K selection theory. The R versus K selection theory says that some organisms will reproduce in a way that aims for huge exponential growth while others are just content to hit the number of individuals that their habitat can support. That is, the carrying capacity and then stay around that level. Species that reproduce in a way that leads to very fast growth are called R-selected species because R is the maximum growth rate of a population when you're talking math talk as we learned last week. Very strongly R-selected animals make a lot of babies in their lifetime and just hope that they make it. If some of the babies get eaten or something, no biggie. There are others where those came from. On the other hand, K-selected species only make a few babies in their lifetime, and they invest in them very heavily. K in math language is carrying capacity, since K-selected species usually end up living at population densities closer to their carrying capacity than R-selected ones. Of course, things aren't so cut and dry in nature, as most animals aren't very strongly K-selected or R-selected. It's actually a spectrum, some organisms, usually smallish ones, reproducing more on the R side and others, usually larger ones, on the K side. Most species are somewhere in the middle. So the reason I'm telling you this is to drive home how bananas it is that humans have gotten to the population size we have. Because we tend to reproduce way on the K-selected side of the spectrum, we're pretty big mammals, usually only have a few kids during our lifetimes, and those kids are a total pain in the butt to raise, but we put a ton of resources into them anyway. So even though humans reproduce K-selectedishly for the past few centuries, 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 350 years. How did this all happen? Well, the short answer is humans figured out how to raise our carrying capacity so far indefinitely, and we did this by eliminating a bunch of obstacles that would have made our numbers level off at a carrying capacity a long, long time ago. These obstacles, you will recall, are limiting factors, and we managed to blast them to pieces in a few different ways. First, we've upped our ability to feed ourselves. Our crazy, rapid population growth started in Europe around the 17th century because that's when agriculture was becoming mechanized, and fancy new farming practices like the 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 to much of the rest of the world by the mid-19th century. Another game changer for the human population came in the form of medical advances. Anton von Leeuwenhoek, father of microbiology, all around really smart guy, was the first modern scientist to propose the germ theory of disease in 1700. And even though it took about a century and a half for people to take it seriously, it revolutionized human health, leading to things like vaccination. Suddenly, people stopped dying of stupid, avoidable stuff, as they had been for thousands of years, which meant that everybody lived longer, childhood survival rates improved, and those kids went on to make their own babies and get very, very old. And we also increased our carrying capacity by not being so disgusting. We figured that you can't just sit around in your own poop and live to tell the tale, so sewage systems became a thing. In Europe at least, it started around the 1500s, but they weren't widely used until the 1800s and we all benefited from that. And finally, we've gotten a lot better at living comfortably in inhospitable places. That is to say, people have been living in deserts and tundra for thousands of years, but in the 20th century, we expanded the human habitat to pretty much everywhere in the world thanks to heating and air conditioning and warm clothes and airplanes and trucks that bring food everywhere from Svalbard, Norway to New South Wales. So for all those reasons and more, humans have been able to avoid that old party pooper carrying capacity, which is good because I don't like it when people die. It's just a downer. And a lot of smart scientists and mathematicians and economists have argued that each person born in the past 350 years has not only represented another mouth to feed but also two hands to work to raise the human carrying capacity, just enough for themselves and a teensy bit more. So then as our population grows, our carrying capacity grows right along with it, like some really steep escalator going up and the ceiling just above our heads. And if it stayed there, we'd all get squished. But it keeps moving. But of course, this can't go on forever. The human population does have a carrying capacity. It's just that nobody's 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 13.4 billion people. Since then, estimates have ranged from one billion to one trillion, which is 1000 billion, so that seems a little extreme. But the averages of these estimates are from 10 to 15 billion folks. Now we need a lot of obvious things to survive, food, clean water, non-renewable resources like metals and fossil fuels, but everything that we consume requires space, whether it's space to grow or space to mine or produce or put our waste. So a lot of ecologists make their estimates of how many people this planet can handle based on an ecological footprint, a calculation of how much land and how many resources each person on the planet requires to live. That footprint is very different, depending on where you live and what your habits are. People in India use a lot fewer resources and therefore space than Americans, for example. Meat eaters require a lot more acreage than vegetarians. In fact, if everybody on the planet ate as much meat as the wealthiest people in the world do, current food harvests could feed less than half of the present world's population. So 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. For instance, if there really were a trillion people on the planet, everybody would have to live, grow food on and poop on a 12 by 12 meter patch of ground, about half the size of a tennis court. So it could be that you could fit 1000 billion people on Earth, but I can guarantee that those people would have a hard time getting along with each other. But how about we stop thinking about ourselves just for a moment? As we 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 through one of the biggest extinction events in recent geological history. We're outcompeting other species for the very basics of life, and eventually, or in the case of oil and water already, we're starting to compete with ourselves as a species. So serious stuff here, but here's a little glimmer of hope. Unlike some other animals, a lot of our actions are based on a little thing called culture, and human culture has brought about some huge changes in the last 50 years. 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. Families in most industrialized countries are getting smaller and smaller. But why? Well, part of it has to do with women. As women in developed nations get more education, they're having babies later in life. And when an animal doesn't reproduce to its fullest potential, meaning it doesn't start having babies as soon as it's sexually able to, that animal is going to have fewer offspring. Also, if you gave women more choices and more education, they might be liable to choose a second career in astrophysics rather than becoming a mother. Another reason for the falling population growth rate has to do with the way that we live our lives. 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. It's a good example of that idea about more hands doing more work to increase the carrying capacity of the human population. Yeah, kids were an extra mouth to feed, but they were also a really important workforce and you could just feed the kids the stuff you were producing. That's what we called a positive feedback loop. As the population grows, the workforce gets bigger, and the place as a result supports more of us. But these days, 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 A, they cost a lot of money to raise. B, they're not bringing in money like they were back on the farm. And C, a lot of people have access to good birth control so they don't have as many oops children. While these factors together are forming a negative feedback loop, the effects of reproduction in this case work to slow down the rate of reproduction. But just because a population's growth rate is decreasing doesn't mean that this juggernaut of humanity is going to stop anytime soon. 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 kinda need to do something about it. And I think pretty much every other species on the planet would agree with me on that.