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Introduction to human evolution

What makes us human? It’s a story seven million years in the making.
When we think about what makes us human, we often think about things like our large brains, our complex societies, our sophisticated technology. This also includes things like our upright posture and our ability to walk and run very efficiently. But when we look in the past, we can see that a number of these features came about at different times and in different species.
Hi, I’m Tanya Smith. I’m an associate professor in the Australian Research Centre for Human Evolution at Griffith University. Today, I’m going to give you an overview of human evolution. We’re going to talk about seven million years of human prehistory. We often think of the early part of the human fossil record as being made up of species that are fairly apelike. When you look at the skull of a chimpanzee– our closest living relative– you can see that they have fairly small brains and large faces. They also tend to walk on four limbs. They’re quadrupedal, as opposed to humans who are bipedal. We know today, though, through modern genetics that chimpanzees are, in fact, our closest living relative.
And the early part of the human fossil record shows that in very good detail. Humans have been evolving in Africa for more than seven million years. The earliest part of the fossil record is pretty spotty. We actually have only a few different bones from species that lived between four and seven million years ago. We recognise them as human ancestors because we think they walked on two legs. They actually had very small brains, similar to chimpanzees. And fairly much, unlike our own brains. We don’t have any evidence that they used tools. And we don’t know very much about their social groups. So when we think of human and our ancestors, technically, we call this whole group hominins.
That would include relatives, as well as direct ancestors, of our own genus and species, Homo sapiens. The record of hominins goes back seven million years ago. We can think of human evolution kind of like a three act play. The earliest scene takes place in Africa seven million years ago, with some of the most primitive members of our human family tree. We call these early hominins different names depending on where they were found and who discovered them, but what unites them is the fact that they were fairly small-brained. Fairly short in stature. And they didn’t use very complex technology. Some of the earliest hominin fossils that we find actually share more in common with chimpanzees than with humans living today.
For example, you can see this chimpanzee skull has a very large projecting face and a very small brain case. This fossil hominin is one of the very earliest fossils we’ve discovered at seven million years. It has a large face and a very small brain and a projecting facial portion, similar to the chimpanzee. The second act in the play or scene– if you will– is made up of the Australopithecines. Again, fairly small-brained, large-faced hominins, which had– in some cases– very large ridges on the outsides of their skull. This is a more diverse group of species which live throughout Africa for several million years. We start to see the earliest evidence for tool use in the Australopithecines.
However, they didn’t yet have the large brains and modern-like bodies that we see in our own species. The last act in the play, the genus Homo. Moving from the Australopithecines– the middle part of the fossil record– to the genus Homo, you can start to see that the face is getting a little bit smaller, while the brain is actually starting to enlarge. The genus Homo turns up about two and a half million years ago in Africa. We start to see an enlargement of the brain somewhere in this period, as well as a realignment of the body to be even more efficient in walking and in running. The genus Homo used tools in a new way in a more sophisticated way.
Over the last few million years, we have a number of different technologies that we can recognise members of the genus Homo. Specifically, Homo erectus were built to be able to walk and run efficiently. Hunt. They certainly produced stone tools with increasing sophistication. And they left Africa somewhere close to two million years ago and started to spread out throughout Eurasia, as well as into Asia. It’s at that point, we start to see a real diversification of members of the genus Homo. One of the most interesting and well-represented species of the genus Homo are Neanderthals. Homo sapiens– our own species, represented by this skull– has a very small face comparatively and an even more expanded brain than the Neanderthal.
By volume, however, the Neanderthal has the largest brain.
Homo sapiens arose sometime around 300,000 years ago. We have evidence from North Africa of large-brained species with a long developmental period. And we start to find fossils, as well throughout Africa, in the last 200,000 years. It’s at that point, we start to see a real diversification of members of the genus Homo. We see a number of really interesting species. Homo floresiensis– for example– we find on the island of Flores, is a very unusual and unique member of the genus Homo. We see other species arise. For example, the Neanderthals in Europe. Very large-brained species. Very robust, large-bodied. Stocky. Interesting and very different than other species that we find– for example– in South Africa, like Homo naledi.
So the radiation of the genus Homo over the last few million years has given rise to a number of different species.
Our species– Homo sapiens– over the last 100,000 years, engaged in some really interesting and complex symbolic behaviours. We start to see things like pierced shells. The use of pigments like ochre. Designing of personal adornments like pierced animal teeth, as well as other abstract forms of artistic expression. This is something that may have given us an advantage over other hominins that were living at the same time, including the Neanderthals in Europe or other species in Africa and in Asia. We’re still trying to understand who made some of the symbolic art. In some cases, it’s actually not clear whether it was our species.
What makes us human? It’s a story seven million years in the making.
Scientists do not agree on every aspect of this story. There is much debate about how the different species of early humans are related, and which species died out without leaving descendants. There are different theories regarding what influenced the development or extinction of the various species. There are even disagreements about how we classify different species.
The purpose of this course is not to try and arrive at a definitive answer to all of the different aspects of this story. Nor are we trying to convince you that such an answer even exists. In fact, what we are demonstrating during this course is how the dating of human fossils contributes to and shapes these debates – changing the story as more and more evidence comes to light. It is the nature of science to continually challenge what we know. The science surrounding human evolution is no different.
In her video, Professor Tanya Smith is providing us with a very concise overview of current perspectives on human evolution. Tanya’s own research has contributed to the changing nature of this perspective, such as the role played by teeth in clarifying human developmental questions.
Modern genetics tells us that chimpanzees are our closest relative alive today. The current perspective on human evolution is that humans and chimpanzees share a common ancestor that lived in Africa six to eight million years ago. This is because all of the earliest human fossils that have been discovered so far have been located in Africa.
We refer to the whole group of humans and their ancestors as ‘Hominins’. The term Hominins includes the relatives and direct ancestors of our own species, Homo sapiens. The earliest specimen that Tanya shows us here is Sahelanthropus tchadensis – dated to around seven million years ago.
Tanya’s description of the ‘three-act play’ gives you a clear framework to help structure this overview of human evolution.
  • Act One: Africa, around seven million years ago. The most primitive Hominins. Small-brained, short in stature and without complex technology.
  • Act Two: Africa, around four million years ago. The Australopithecines. A diverse group, small-brained, using simple tools.
  • Act Three: Africa, around two and half million years ago. The genus Homo. Brain starting to enlarge, body starting to realign, more sophisticated tools and technologies. Around three hundred thousand years ago, Homo sapiens arose.
The genus Homo left Africa around two million years ago and began their spread into Eurasia and Asia.
This next video shows a simple timeline of some of the key members of our three-act play.
(Note: Ma refers to million years; ka refers to thousand years.)

This is an additional video, hosted on YouTube.

Your task

Select the comments link below and tell us what you think. Does the ‘Three-act play’ framework help you to more clearly organise the information on human evolution?
Don’t forget to use the 3Cs when you are responding to each other’s comments (Curious, Constructive, Compassionate).


Australian Museum (2016). Hominid and Hominin – What’s the difference?
Pontzer, H. (2012) Overview of Hominin Evolution, Nature Education Knowledge 3 (10):8
Smithsonian National Museum of Natural History (2018). What does it mean to be human? Introduction to Human Evolution.
Stringer, C. and Andrews, P. (2012). The Complete World of Human Evolution, 2nd Ed. Thames & Hudson.
University of California Museum of Paleontology (2018). “An introduction to evolution.” Understanding Evolution.
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A Question of Time: How We Date Human Evolution

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