Human Population Growth – Crash Course Ecology #3

If being alive on earth was some kind of contest,
humans, I think, would win it hands down. As a population of organisms, we’re the Michael
Phelps of being alive, only we have like 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 that 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 1 billion. And it doubled again just 80 years after that,
and doubled again just 45 years after that. We are now well past 7 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? [Theme Music] 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’ve 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
you know, with the ramen, you get more, whereas with the handmade stuff, it tastes
better — higher quality. 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 vs. K Selection Theory. The R vs. 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. The 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, you know, a spectrum. Some organisms, usually small-ish 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 anyways. So even though humans reproduce K-selected-ishly,
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. Well, how did this all happen? Well, the short answer is that 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 van 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 vaccinations. 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, ’cause I don’t like it when
people die, it’s just, 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 1 billion
to 1 trillion, which is one thousand billion, so that seems a little extreme, but the averages
of these estimates are from 10-15 billion folks. And 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 a thousand
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 every 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 that 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 like, sexually able to — that animal is going to have fewer offspring. Also, if you get women more choices and more
education, they might be more 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 work force and you could just feed the kids the stuff you were producing. That’s what we call 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. All 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 our 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 kind of need to do something about it. And I think pretty much every other species
on the planet would agree with me on that. Thanks for watching this episode of Crash
Course: Ecology, and thanks to all the people who helped us
put it together. If you want to review anything from this episode,
there’s a table of contents over there, and if you have any questions or ideas or
comments, we’re on Facebook and Twitter and of course, down in the comments below. We’ll see you next time.

100 Replies to “Human Population Growth – Crash Course Ecology #3

  1. 7:25 That is assuming everyone lived on a flat plane. But as our large cities have demonstrated, you can fit a lot of people on that 12X12 plot of land. Just stack them up in a high-rise. A 100 story building could fit 100 people on that single 12X12 plot. And 100 stories isn't that high.
    The Twin Towers were 110 stories, and they weren't even the tallest buildings.

  2. People have been saying, "Our changing society can not support the current growth rate for much longer" for well over 2500 years. They have all, so far, been wrong. Why is now any different? Every single generation for the last 1000 generations have had people warning about the dangers of over population. When asked why they were right while everyone before them was wrong, they have all said, "We know more than they did."
    If you can't give a convincing argument why you are the first one out of all of these others (who all also thought they were the first to be right) are right, I don't think anyone should take your arguments seriously.

  3. we dont need fossil fuels, we have allot better solar now and we recycle metals at a high rate. Who is too say humanity shouldn't be in the trillions 100 years from now? The More humans the better, we may have enemies out there we dont know about yet. what if the Robots Turn hostile on us and try too terminator us all?? pollution in the western world is dropping like a stone.

  4. Feeling so proud of the One Child Policy right now. Well now it's the two child policy but same difference. Hats off to China

  5. I don't think we should worry too intensely about overpopulation. The word "overpopulation" is deceptive because it suggests that we actually know the carrying capacity for planet earth. We do not. We have estimates, and nothing can definitely tell us whether those estimates are good or not. Furthermore, no human has a comprehensive enough perspective to tell another human being whether or not he should be alive, and that's what people worried about overpopulation often end up doing. Past overpopulation curbs like government-distributed contraception were easy roads for other agendas, like the forcible sterilization of minorities in America. Basically, we can't do "population control" with anything short of dictatorship (and often murder). I realize that sounds extreme, but if you look at China's 100,000 girls-abandoned-a-year and the sterilization of about 1/3 of Puerto Rican women in the 60's, it's not extreme at all.

  6. Some of you people are showing authoritarian streaks that scare me…if we want to bring down the number of births, our culture is not the problem. We're barely at replacement levels in the U.S. and they're below replacement levels in Europe. The problems come from places like China, India, and the middle eastern countries.

  7. If causing extinction, consuming non-renewable resources and torturing living creatures was some kind of contest…

  8. Poor countries are overpopulated since people have 5+ and stable economic ones have 1-2 children . It is a political issue and big corp i making countries poor and there you have it.

  9. Shout out to reducing your environmental footprint by eating more Plant-Based <3

  10. how about we start adopting children with no families instead of making our own? There are a bunch of kids with no families! The movie "Lion" really touched my heart.

  11. Solutions:

    One child policy like in What Happened to Monday.
    we kill each other over massive debts and oil.
    Genetically Modified Cordiceps fungi.

  12. IF you Must have kids then 1 kid is the most optimum choice. 2 is the absolute maximum! More than 2 is a big ol' NOOOO!!!!!

  13. "Human population is a problem that needs to be dealt with…." Let's hope that enough of us figure out that the MAIN way to deal with this problem is to promote VEGANISM!!!!!!!! Watch Cowspiriacy, Earthlings, What The Health, Forks Over Knives, etc. Read The China Study, World Peace Diet, etc. Educate yourself!!!!!!!!! Be the change you want to see in the world.

  14. please research and advertise permaculture and the effect of secondary secession in humans… please also do a video on more minor things like how limiting human population could be good for us in more unusual ways like parasitic tools instead of our simi peditory behavior

  15. Dude, you didn't identify what will be the limiting factor for human growth! You mention space but nothing about vertical farming or living… Pretty sure folks in new york or shanghai are living in less than 12×12 meter per person space.

  16. If you seen a map of the earth and overlay it with a map of the distribution of people on earth, you will soon realize that overpopulation is nothing to worry about. Not only that but the birth rate is halving across the world as developed countries get wealthier and more educated. Population wise, we're fine.

  17. The Catholic Church is a problem, because they are not only against abortions, but all contraceptives (!!). They want to keep women down in their traditional role as wives and mothers of large families. Everything else they deem immoral. They even fight against governments in predominantly Catholic countries (like in the Philippines) that want to introduce free contraceptives: the wellbeing of the people is less important to them then their women-hating – sorry: "moral" – ideology. In the Philippines they also tell the faithful in sermons that contraceptives are extremely unhealthy, dangerous. Some priests even spread rumors that contraceptives make women ugly and smelly. In Africa, Catholics were adamant in their anti-contraceptives stance even when HIV was spreading dangerously. The Catholic Church is generally against talking about Human Population Growth aka "Overpopulation" (a taboo word in our days, since environmentalist got slandered – also mostly thanks to the Vatican – as racists, genocidal and eugenicists!). Since they quasi hijacked the UN conference on Population and Development in Cairo (1994), people talked less and less about population. Now it is hardly ever spoken about. Did things get magically better? Not really, the sixth mass extinction is in full swing. Sad, that hardly anyone cares. So damn depressing.

  18. Ok but I think he was talking about the second agricultural revolution cause the first actually started in the middle east (mesopotamia) about 10,000 years ago. A long time after that, the second agr. revolution rolled around and out popped more effective farming, gmo's from that one dude who spent a long time in Mexico developing high yield seeds and all that, etc.

  19. Hank Green!! Who is it that suggests human population should be the size of whatever the Earth can sustain as being hunter-gatherers!? I MUST KNOW!!! NAMES!?!? Too intriguing!!!

  20. A global 1-2 child policy would probably be very beneficial at this stage and a lot kinder than having loads of people die from famine, drought and natural disasters. It also spreads the responsibility and consequences of the problem more evenly.

  21. Wait, wouldn't the population growth be best described as linear (and not exponential) if it just doubles over those time periods instead of squaring? Hmm. I suppose that if you "zoom in real close to the graph of an exponential curve" that it would appear linear. Still, I'm confused.

  22. Well of course, I agree with man made climate change.
    But let me ask you , did you breed ? The biggest contribution one can make towards the destruction of the earths biosphere is the creation of humans . The ecological footprint that comes with breeding is unsurpassed….. I am not responsible for me being on earth but I am responsible for the human climate changers conceived by me . Therefore I choose not to breed., most people however choose to be self interested hypocrites…….

  23. So there are two "white" people who both remark about how my cold apartment feels great, however my darker skin ex tells me at a motel that she is uncomfortable with the air conditioning there up as high as it was (about as high as at my apartment). So i started wondering about the snowcapped mountains and the low temperatures and the higher temperatures you find in the lower elevations and then the demographics of the people who live in either places and you know what i found right? Who is it you dont find alot of in the higher elevations and who is almost always found in the lower elevations? Lets say oakland ca as opposed to salt lake city ut, you factor in other variables like jobs, perhaps family and maybe favorite sport franchises and you then see discrepancies in the skin color of the two populations but am i crazy for saying that you dont see many people from oakland going to salt lake city to ski during the winter? You wouldnt see my ex there or living there but you would see all kinds of "white" people who liked my cold temperature apartment. But yet and still i bet people think about the differences based on the misconception that dark skinned people are cursed by a dummy who doesnt seem to get that he doesn't exist and that the people living in those wide open spaces with the snow capped mountains are there because They All Like The CLIMATE there? Well i do know of someone in those jehovahs who didn't like the idea of sodom and gomorrah and lives in the mountain areas because he wanted to leave that religion but hesitated due to that misconception about sodom and gomorrah outside of religion. But that's what i found taking time to think about something other than god and creation a subject scientists tell you is not why you're here. Real simple but complicated by the mistaken belief in god/creation.

  24. Does anyone ever stop to think people live where they do for no other reason than they like the climate there? Not because of their skin color? It just Appears that way due to a misconception about why your here?

  25. Im usually cautious about hearing people talk about this topic because its been historically used in very dangerous or problematic ways. Im glad this handled this topic responsibly

  26. the solution to human carrying capacity is not going to be found on earth, I mean that quite literally. It is not to become vegetarians, or produce more GMO's, or filter salt water, or become more ecological. Those are all irreversible factors of the human race that as long as we exist will always be there, sure we can slow them down, but the peak will eventually hit. Instead, all of our focus these days should be on colonizing and terraforming nearby planets and transitioning from a planetary civilization into a type 2 civilization. I can assure you that the process will start within the next 100 years, the move to mars is imminent, and from there on out other rocky planets and eventually our galaxy. That, is the real solution to the problem.

  27. at 4:15 he is wrong he is actually talking about Louis Pasture not Antonie van Leeuwenhoek. There are some inaccuracies in your science facts. van Leeuwenhoek used the population of Holand and its respective landmass size to estimate the worlds population base on its landmass.

  28. such a good video! You should explain in more details and use examples to make it clear!! thank u dude!! I'm here to let u know how u should improve!! have a good day ..

  29. Does anyone have a source for the quote about how if everyone lived as the wealthiest do we would support less the half the people? I cannot find anything saying that specifically but I find it interesting. Also what does he mean by the wealthiest? Wealthiest 1 billion maybe? Or wealthiest countries or millionares and billionares? I found one source that you would need 4 times the resources to support everyone living as americans do.

  30. This video was published 6 years ago and here I was thinking ~these days people are obsessed with the idea that world won't be enough for human population So you should decrease. But obviously the idea is not new.

    Well, I don't like this idea And find it very weird. We worry for the very very very very…… long distanced future ignoring the unpredictable changes world may go through and also ignoring the human capacity for developing. Even tho let's say there will be So So So……… many many humans on earth, those humans won't be the same, will have a better technology and probably will find a way to live nicely.

  31. But the definition of carrying capacity is that the environment can host a maximum amount of organisms indefinitely and in a sustainable manner, so applying that to humans' current situation, I don't think that the carrying capacity of Earth is 10-15 billion, as we are already seeing signs that 7+ billion isn't sustainable through climate change and the endangerment of other species. In my opinion, we've already passed the carrying capacity of Earth, and with the human birth rate overwhelming the death rate, it not super good.

  32. inter net says `Over 17,000 humans most children die each 24 hours (a day) from Over population ..U want to raise children in a loving environment .. Please just ADOPT and maybe get u and as many plp around you to get STERILIZED …….. why do children have to die -just because u want a child that may look like you!!

  33. i still fine it so strange how in the two videos i watched three chapters were summarized in 10 min vids which would of taking me a hour or more ….. thank you so much

  34. I'm not that keen on the phrase "meat eaters" because the difference between cattle and chickens is about the same magnitude as that between chickens and vegetables. I didn't know this previously, but in the chart I just pulled up (to confirm my previous statement), lamb is another 50% worse than beef (in CO2 emissions per kg, rather than per calorie, which would make more sense).

  35. If you haven't looked at modern farm equipment for a while, check out Top 10 Corn Harvesters of the Half Century of Progress Show at bigtractorpower (YouTube). Couldn't be more relevant to the theme of this lecture.

    Then check out John Deere 24 Row Corn Head or Best 2018 Big Farm Machine Video Clips Working Side by Side on the same channel.

    Also worth watching: The Discovery Channel documentary, World's Biggest Ship (2013) on the construction of the Maersk Triple-E cargo ship (most of which can be found on YouTube).

    Humanities recent agricultural and distributional progress is mind-blowing (at least as concerns a MOAR-heavy definition of "progress").

  36. I see the argument towards vegetarianism to feed the world, but there are nutrients and vitamins that you can't get from plants and only from meat. If you want a healthy population, you need some meat in your diet.

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