One of the fantastic opportunities we had in South Africa was to visit the collection of fossils at Witwatersrand University. They have a collection of about 30% of the fossils found in Africa that tell us about how we evolved from ape-like creatures into modern humans. Professor Lee Berger took us though some of the highlights of the collection, piecing together three million years of evolution in the process. One of the most interesting things that the fossil record reveals is that we went through a period of extreme giantism. These were people routinely over 7ft tall, they were huge. This was before we turned into the modern humans of today.

Lee - You've probably heard the myth that ancient humans were tiny and some of them were tiny. But, as we moved through the period of 0.5 million to 300,000 years ago in Africa we move into the sort of mystery period where there's just a tiny handful of fossils. The ones we find from that part are incredibly intriguing. By this time you're going to begin seeing Neanderthals in Europe. Inside of Africa they go through one of the most incredible things that we've only just begun to realise. They go through a period of giantism. What I'm pulling out of this bag may shock you!

Chris - Oooh!

Lee - Hahaha.

Chris - What we're looking at is the most enormous femur: the bit that forms your hip joint. That's huge. As a doctor I know how big they normally are, that's huge.

Lee - They are huge. That's so big we can't even calculate how big this individual was. You would need an NBA basketball player to get someone of the height someone like this would have been. Something like over 7 feet tall.

Chris - You don't think this one's just an abnormality?

Lee - No because we found a lot of them. Everywhere we find them we find them enormous. These are what we call archaic Homo sapiens. Some people refer to them as Homo heidelbergensis. These individuals are extraordinary, they are giants.

Chris - Does it coincide with a time when there was enormous amounts of resources, lots of food which meant they could afford a huge body size like that?

Lee - Actually it might have been just the opposite. That is, it was a period when there were larger amounts of grassland evolving and there were lots of giants adapting to that grassland. Giant buffalo with horns three metres across if you can imagine that. These individuals in that very rugged environment, that tough environment, seemingly were using their body size to enforce themselves into what was a very dry and tough period.

Chris - So when would he have been around?

Lee - This particular individual existed probably about 350,000-400,000 years ago.

Chris - How long did people with this giant stature exist for before they started to shrink again?

Lee - We have no idea but we do know that the next time we start getting a good window in is 100-150,000 years ago when we're here. People of our stature, our body size. This experiment was relatively short-lived (a couple of hundred thousand years).

Chris - So that was all happening about 300,000 years ago but what about if we wind the clock back now to almost the very beginning? To the earliest human ancestors who walked around on two legs. These were the Australopithecines and they emerged about 3 million years ago. The first ever example was unearthed by the famous palaeoanthropologist, Raymond Dart. In the early 1920s he was working with his students in the Taung limestone works which is in the Harts Valley in the Bechaunaland, South Africa. There, he discovered what turned out to be one of the most important fossils of all time.

Lee - This little brown box I'm opening up is the actual box Raymond Dart had built, back in 1925 to hold, arguably, the most important single human ancestor fossil on the planet. You're about to join a really exclusive club of people who've actually seen and touched it. This is the one that defines what it is to be an early African ape-man.

Chris - This is 3 million years old?

Lee - This is about 2 ½ million years old. We've actually largely dated it by comparing it to other fossils that have been found since. It is an awe inspiring fossil but, remarkably still, the only fossil that was ever found at the Taung site. It just happened to be this little child which is the first fossil of an early human found in Africa. This started the entire science. In fact, you can even argue that things like genetics and the study of our own origins came out with this fossil. Discovered in the Taung lime quarry, it was sent in a box full of baboons to Raymond Dart and if it had arrived on almost anyone else's desk at that particular time they might not have recognised it. What he pulled out of that box, the first thing he saw - if I pull out this little plastic bag - is that remarkable little thing: half an endocast of a brain of a little child. Immediately, Raymond Dart recognised that he wasn't holding a baboon brain in his hand. It wasn't even a brain of a chimpanzee. It was far too big. He was holding something that no one had ever seen before. He probably would have used the term, 'a missing link.'

Chris - That's totally extraordinary. How does something so soft and blancmange-y as a brain actually get preserved?

Lee - Well, because it doesn't. That's not actually the brain. What that is, is a cast of the interior of the skull. very time your heart beats, as your head is forming as a child, it beats am impression of the surface of the brain onto effectively the inside of your skull. When a skull is up in these remarkable fossilisation situations there's a perfect impression - a perfect image of your brain on the inside of that skull. When it fills with fine sediments we then have a perfect cast of the brain.

Chris - You can literally, looking at that from the side, see the three major parts of the brain. I can see what's going to be the cerebellum, the hind brain at the back, there's the temporal lobe - which is us is adjacent to our ear and then the frontal lobes where I'd be thinking and planning - I don't know whether this would have done much thinking and planning. That's an incredible fossil.

Lee - It is one of the most remarkable fossils in of itself, that you'll ever see. Look at the veins on the surface! The blood supply to the brain is actually preserved on the surface of that. Raymond Dart turned this little thing over just like I'm doing right now and looked down and saw this was not a rearward facing point of attachment facing this skull in the spinal cord. It was vertically positioned.

Chris - That says it was not ape-like. That's homo.

Lee - 'I walk on two legs,' that's what it spoke to him as clearly as if it were written on the fossil itself. If that had been all he found it would have been fantastic but it wasn't all he found. Inside of another block he saw this little mushroom-shaped attachment and in it he saw the back of a mushroom-shaped ...

Chris - Oh my god!

Lee - Yes, oh my god!

Chris - I've just got a glimpse of what's going to come out of this bag.

Lee - He took his wife's knitting needles and started chipping away at it. On December the 21st, 1924 that rock broke away and he saw that.

Chris - It's a face. I'm looking at a face. It's phenomenal.

Lee - You're looking at maybe the most famous face in all of palaeontology.

Chris - It's perfect.

Lee - It's absolutely perfect because it doesn't have just the top, it has the bottom.

Chris - It's got a jaw and a face to go with it. It's still quite monkey-like though isn't it?

Lee - A little bit. It doesn't have quite the prognathism that a young monkey would have and what it certainly doesn't have is a big canine. We're going back to something that's transitional. It's a bit of the way between us and them. It's our link. This little child met a tragic, tragic end and about 3 ½ years of age. I'll do something for you. I'll put it all together, the whole Taung child. Reunited, after being 2 ½ million years underground.

Chris - I think that probably is the most awe-inspiring experience, or one of them, I've ever had.

Lee - It is, it's about our experience. Do you want to touch it?

Chris - Go on then. So if I touch this, how many other people will have had the opportunity apart from Raymond Dart to have done that?

Lee - No more than a few hundred scientists and a few dozen people who aren't scientists.

Chris - That is absolutely incredible. To say I'm blown away would be an understatement actually. It's when I saw the face staring out at me through that plastic bag, it's almost moving me to tears. It's just so incredible and delicate and perfect.

Lee - Yep, and 2 ½ million years old. And it's our story.

Ben - The emotions were running quite high in that room and it was an honour to see that skull. But if you're wondering what happened to that child, it was actually snatched away and killed by an eagle. The fossilised bones of the skull have preserved the scratches from the bird's talons. They compared it to baboons and they could see that that's what it was. That was Professor Lee Berger showing us some of the most important human ancestor fossils ever found.