Painting a picture of human history

They say a picture paints a thousand words, right? Well, sometimes it can tell us even more. Paintings on rocks have helped scientists solve the mystery of when the first modern humans settled in an area, how they diversified over time and even if they had different accents. Chris Smith spoke to Jo McDonald, Director for the Centre of Rock Art and Management at the University of Western Australia.

乔,我们目前参与的一个项目the dampier archipelago - that’s known as Murujuga Aboriginal people that live there. It’s in the coastal Pilborough, so that’s about 1500 kilometres north of Perth. Since 7,000 years ago it’s been an archipelago but before that it was an inland range.

Chris - How long do we think modern humans have lived in Australia?

Jo - We are pretty sure that modern humans got here about 50,000 years ago. We’ve got archaeological sites all the way across the top of Australia which are increasingly coming up with that date range between 45 and 50,000. We’ve also got caves with similar aged occupation in Tasmania so people got there and moved around pretty quickly and occupied almost the entire landscape.

Chris - They sure did. And they left a lot of very impressive paintings and those paintings have been added to over many years, so tell us how you study them?

Jo - We record what’s there and in different parts of the country we can obviously see different signs of what people have done through time. We, at the moment, suspect that when modern humans got here they did settle fairly quickly across the majority of the continent. But because they were basically moving into a naive continent, one that was not used to dealing with humans that they had a pretty open signaling system and they had a homogeneous set of art styles which we find across most of Australia.

Chris - Is that just founder effect that they probably brought in some artistic styles as the first incomers to Australia but then, as the population diversified, because this place is huge there wouldn’t have been the same communication on the same timescales that we have today obviously? Then it would in the same way accents evolve - you have a different accent to me - that would have led to different art styles?

Jo - Yeah, exactly right. The genetics is now showing, and we’ve suggested before in our modeling that regionalisation probably occurred in the pleistocene because you have some of these earlier engrave styles which show diversification. The genetics is now coming out as wel. By 25,000 years ago Aboriginal populations in Queensland had different accents to people in Western Australia.

Chris - Can you date the pictures to work out what’s in the art and how those styles relate to different time zones in that migration process?

Jo - We are getting much better at dating the pictures. We still have quite a lot of difficulties with engravings because they are, of course, they don’t have anything organic in them. But pigment art and art that occurs on surfaces that forms geochemical crusts we are getting really good at getting very small amounts of the pigment out and dating that. Or using uranium, thorium and various other techniques to actually mine in and find layers of systems that can be dated in these crusts.

Chris - So when the pigments are put on the rocks, chemical changes over time begin to happen and you know what rate that sort of happens at so you can trace back to when we think the art was first put on the rock?

Jo - We are beginning to understand that. There’s a team from Melbourne University who’s working on that in The Kimberley at the moment and they are beginning to be able to demonstrate that these are closed systems. That you can in fact get isolated uranium threads, if you like, in the crusts and they can go in an mine those and get individual dates and see how much of the crust was there before the pigment, where the pigment is, and then what has happened subsequently. So you can actually date a sequential lot of actions on the rocks on the rock surface, yeah.

Chris - What story’s emerging when you look at this?

乔,我瘦k what we’re beginning to see is that people have seen the landscape very differently through time. They’ve obviously always marked it in a way. I think humans are inveterate doodlers, if you like, and we have writing now that Aboriginal people had used rock art as a way of, in fact, telling information about themselves. Telling information which would distinguish them from others, and I think people have always liked producing beautiful things. And I think Australian rock art is a really good example of this extraordinary aesthetic which is incredibly full of information and can tell us all sorts of things about the people who made it.

Chris - But critically, talking to modern day Aborigines because, obviously, what they have is a rich history which they pass on through generations, can you tie what they tell you to what’s written in those pictures?

Jo - Well, yes you can. We’ve been working with the Martu in the western desert who only made their first contact with white people in the 60s and 70s. They, therefore, still have a connection and a whole set of narratives about that landscape which sometimes engage with rock art, sometimes don’t. But certainly, where you can see these dreaming mythologies going across the landscape, and you can see the rock art, you can see patterns archaeologically which engage with that set of narratives and allows you to see how people have, in fact, changed that focus on the landscape through time and have marked those places differently through time and that rock art is recursive. People will come to a location, an important water hole for instance in the desert, there will be all this rock out there for them. It won’t necessarily be part of their current marking system but the Martu say that the engravings have been there and been left by their ancestors. So these things which are there and which are pictures of people or animals and various different things or tracks, they say have been left by the ancestors. They recognise that they were done by people other than them but they’re part of their narrative. It allows them to understand how different people have moved across that landscape and have engaged with them.

Chris - One big question that we just don’t know the answer to yet is when these individuals, the early ancestors, first came to Australia they did so 50,000 years ago or so, but then no-one came since - or did they? Because the genetics and other archaeology seems to suggest that one bunch of people came and they were the founders, and no-one came afterwards. Do we know why only one group of people came?

Jo - I don’t think we do know that. I think certainly the genetics is suggesting that that’s exactly right that we don’t have multiple waves, and that was certainly the original hypothesis about how Aboriginal people look very different in Northern Queensland to Southern Tasmania that there were obviously different waves of people through time. It’s been disproved by the most recent genetics. Obviously there is contact between Southeast Asia and Northern Australia. We’ve got indications that Macassans came to harvest Trepang - the sea cucumber - that’s the last 6 or 700 years; it’s not very long. But there is that contact so people could have come between once boat travel was the way to do things.

Chris - Dogs turned up, and we know dogs came after people.

Jo - That’s right. And that’s about 4,000 years ago so there seems to be some sort of introduction by people at that stage, but there doesn’t seem to be any major influx of new genes at that time.

Chris - Until us lot turned up?

Jo - Till us lot. That’s right. Came and messed things up. Yeah, that’s right.