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The spread of humans

Richard Baldwin discusses climate change through human history (Phase 1).
Welcome back. I hope you’re ready to start digging into the history of globalisation. This step, we are going to go way back, a couple 100,000 years back. We’re going to look at ancient globalisation– the first phase. This phase lasted 180,000 years. It’s a long time. The longest phase by far. But the video is only going to be a couple of minutes long, because there’s only one really interesting thing that happened. And I’ll leave you into suspense, but I want to get to some background first. And this isn’t background just for economic globalisation to understand in this course. It’s some background of things that you should know as a human being.
And that is, what has happened to the Earth’s climate while humans have been on this planet? What I’m going to do is show you a graph over time of how the climate has evolved. Now, with this graph, I labelled it 200,000 years of climate change. Down here, it starts at 200,000 years before present. That’s essentially when humans appeared in Africa. And it goes right up to the present there. On the vertical axis, what we have is temperature difference to today in centigrade. So right here is zero. That’s about the temperature it is today. And as you can see, one interesting thing of this is that the temperature today and the temperature when humans emerged in Africa aren’t too different.
It was about the same. But soon after humans emerged, the world went into an ice age, declined quite steeply, and then came out to a very warm peak. And you’ll notice that warm peak is way warmer than it is now. But then it started sliding back into an ice age. Started up a little bit. And it had a local spike, at about 80,000 years ago. And that’s when humans left Africa. They went across the Red Sea route into the Middle East. And from there, started colonising the world. The world, at this time, started getting colder and colder, reaching a maximum ice age at about 19,000 years ago.
And this is part of the spread, because as the world got colder, more of the world’s water got locked up in ice. And things that are now sea were flat land. For example, you could walk between the Netherlands and the UK during this time. After that, the climate, for reasons that aren’t absolutely clear, warmed. And that’s not what’s so unusual. We can see it going up and down. But from about 11,000 years ago, it’s stabilised. So for the last 10,000 years or so, the climate’s been relatively stable. And that’s when human civilisation emerged. Everything you know about human history, all aspects of human history, emerged during this time and have been stable.
You can see the spike at the end there. That’s what we’re worried about with global warming. And it’s easy to look at that spike and say it’s nothing compared to the previous one, but you have to remember that there are seven billion humans on the planet here, and there was only a few hundred thousand on the planet back then. So that’s the background. What we’re going to do it the next step is actually look at the sequence in which humans colonise the world. And what I would like to do before we turn to that is explain, roughly, how they established that sequencing, because it’s actually kind of fascinating.
Scientists have used the genetic of current populations and compared them across populations to see how long ago the populations diverged and how long they’ve been in a particular place. Now, the way they do this is by looking at the DNA, the genetic code, that resides in one particular part of the human body called the mitochondria. Now, this one uniquely comes only from your mother so you don’t get the mixing and matching you get for most of your genes. And what you can do by looking at the mitochondria of two populations when you know the rate of mutation is determine how long ago they had a common ancestor.
So using this massive amount of data, they make a rough picture of which continents humans went to first and which groups of humans then went on to colonise other parts. So I’ll just stop right there, and we’ll come back with phase two.
Phase 1: Humanising the Globe
Modern humans appeared in Africa about 200,000 years ago. At the time, the world’s climate was not very different than it is today, but that soon changed.
Climate change since the first Homo sapiens
Since the beginning, our species has been knocked about by climate changes that make today’s global warming look like a spring rain.
Out of Africa
Modern humans seem to have left Africa for the first time around 125,000 BCE, but genetic evidence suggests that they did not survive. There was a second “out of Africa” migration and again around 80,000 BCE and this one “worked”. Genetic evidence suggests that all non-African humans today are descendants of these migrants (see the Science reading below if you’re interested; it’s a fascinating story).
Once out of Africa, humans started to roam the planet. Scientists have established the sequence of colonisation using genetic evidence gathered from current populations living in nations all over the world.
Once you’ve finished the video, please turn to the article in the next step which provides a bit more detail on Phase 1, the climatic changes, and the genetic evidence that helps us understand the order in which the earth was colonised by modern humans.
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International Affairs: Globalisation

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