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Video transcript

if being alive on earth through some kind of contest humans I think would win it hands down as population of organisms were 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 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 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 let's say you're shopping for dinner and bear with me we're gonna 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 dollars a pound they're both noodles to both food but you know with the ramen you get more whereas with the handmade stuff it tastes better higher quality what 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 our 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 our 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 okay in math language is carrying capacity since K selected species usually end up living at population densities closer to their carrying capacity than our selected ones of course things aren't so cut and dry in nature's most animals aren't very strongly K selected or are selected it's actually you know a spectrum some organisms usually smallish ones reproducing more on the our 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 all mal 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-selected dish leave for the past few centuries our population growth has been looking suspiciously like that of an R selected species an exponential growth even for our 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 our 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 proposed 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 and Europe at least it started around the 1500s but they weren't widely used until the 1800s and we all benefited from that finally we've gotten a lot better at living comfortably in inhospitable places that is to say people have been living in deserts and Tundras for thousands of years but in the 20th century we expanded the human habitats 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 it's just a downer and a lot of smart scientists in math missions and economists have argued that each person born in the past 350 years 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 a population grows our carrying capacity grows right along with it like some really steep escalator going up in 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 thirteen point four billion people since then estimates have ranged from 1 billion to 1 trillion which is 1,000 billion so that seems a little extreme but the averages of these estimates are from 10 to 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 ecologist 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 in 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 the 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 in 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 and 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 resource 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 out competing 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 percent per year in these days it's declined to about 1.1 percent and it's still falling families and 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 like sexually able to that animal is going to have you or offspring also if you give 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 following 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 extra mouths 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 call a positive feedback loop as the population grows the workforce gets bigger and 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 see they're not bringing in money like they were back on the farm and see 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 but just because our populations 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 applied 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
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