Subtitles section Play video Print subtitles - [Sal] This timeline here covers 200,000 years, from 200,000 years into the past, to the present. And just to get a sense of the scale of this, if we were to go 2,000 years ago to the time of the Roman Empire, that would be roughly here on the timeline. If I were to say, when were the pyramids built? That would be roughly there on the timeline. So by human standards this is a very long period of time. And I didn't choose this time span arbitrarily. 200,000 years is about how long we believe anatomically modern humans have been on our planet, our sub-species of Homo sapiens sapiens. Now the reason why I show these stone tools is because the ages, the periods, of modern humanity, or even pre-modern humanity, are named after the types of tools that have been found in archaeological digs. So most of even pre-human, or near pre-human, and human history, has been the Paleolithic period, or old stone age. Paleo, paleo for old, lithic coming from lithos for stone. So Paleolithic. The old stone age is the great bulk of human history. And there's also a Mesolithic that comes about 15,000, 20,000 years ago. But then around 10,000 years ago, the stones have a much more polished appearance to them. Things like this. And so that period from about 10,000 years, starting with about 10,000, 15,000 years, depending on what part of the world you look at, is referred to as the Neolithic period. Neolithic, referring to new stone. And on top of this timeline, I have also shown what's happening at a very large scale, climactically, on the Earth. So these blue periods are ice ages, and these reddish orange periods are the periods in between ice ages. And so you can see the last ice age ended roughly 15,000 years ago, and it began roughly 110,000 years ago. Now I'm giving you all this context about these Paleolithic, Neolithic, and the ice ages, because we're gonna talk about probably the most important series of events, or innovation, in all of human history. And that is agriculture. Agriculture. For most of human history, over this Paleolithic period, over most of this timeline going up until about 10,000 or 15,000 years ago, our ancestors were hunter gatherers. They would have to chase the game wherever it might be, they couldn't settle down in one place. Maybe there were a few that were near some sources of fish where they might be able to do some basic fishing. But they would have done hunting like this. They would have done gathering, which means getting berries or mushrooms where they could find it. It probably was eating a lot of things like insects, and that is most of human history. But then around 10,000 or 15,000 years ago, we have the advent of human beings taking nature into their own hands. Instead of saying, let's just follow the game wherever the game might migrate to, let's actually domesticate these animals. Let's take some of them, start breeding them so they're more suitable for human consumption, so that they are easier to raise, maybe more robust, and we will breed them, and we will raise them for milk, for meat. We also started to domesticate plants. Instead of saying, okay let's just gather those berries there where it happens to emerge, oh let's actually start to plant things. And on a very predictable way, be able to harvest them, and so be able to have a more predictable food supply. Both of these things allowed human beings to have a higher population density, to start to settle down, to have a more sedentary life. And this is a huge, huge, huge deal. Just to get a sense. We believe that the carrying capacity for the planet, for human beings as hunter gatherers, is 10 million people. And that is what we estimate the world population was around the time of the last ice age, or shortly afterwards. And that's because a tribe of 100 hunter gatherers is going to need 50 square kilometers to 100 square kilometers to hunt and gather from, or actually 500, from some of the estimates I've seen. And it might seem like a lot of area that you would need to hunt and gather from, but imagine that you and your family had to go live in the woods now. How much food could you actually find? You'd have to walk miles and miles per day, if you're trying to hunt, you'd have to walk miles and miles per day to get whatever wild grains or berries, or whatever, or mushrooms, or whatever, or insects, that you might consume. But then with the advent of agriculture it allowed for a much, much higher density population. In fact, going from the birth of agriculture, which happens in the Neolithic period, the dawn of agriculture coincides with the Neolithic period, they're often used somewhat interchangeably. Going from that period 10,000, 15,000 years ago, to the time of ancient Rome, so we're on the order of 10,000 years, the world population with agriculture exploded from 10 million to roughly 250 million. And that's 25x. And we know that from the time of Rome 'til now, another 2,000 years with agriculture, our population has gone up 28x, it's growing exponentially, to seven billion. And there's no way that we could have had this level of density without agriculture. Now a key question is, is why did agriculture emerge right then? Well one theory is is, well it seems to be only, and I'll say only in quotes, only a few thousand years after the end of the ice age. Maybe you had positive climate change, at least from a human point of view, that allowed land to support agriculture. That seems like a reasonable theory. Although you might say, well we've had other periods where we didn't have an ice age, how come we see no evidence of agriculture then? And one counterargument or explanation I've heard for that is, anatomically modern humans started to emerge around 200,000 years ago, but that doesn't mean that the way they thought, or that their brains were the same as modern humans. And so maybe in this period the human brain just wasn't capable of performing, or thinking of agriculture. Other theories are is that the human population through hunter gathering kept increasing over time, and it was right after the last ice age that you really got close to this critical mass of population, at which point, for every extra human to be born, another human would not be able to live, or not be able to be born, because there was a fixed supply of food as hunter gatherers. And so you could say out of necessity, maybe a tribe here or a little group there, started to say hey, well what if we started to domesticate some of this cattle? Or if we started to plant crops? All of a sudden they would start to have a higher density and their population could increase. And not only would they be able to survive, but they could also be very dominant in things like conflict. Once you start having agriculture, and as agriculture advances, as I mentioned, these people could be more sedentary. They wouldn't have to move around.