Professor Michael Petraglia has always been drawn to the distant past. Growing up, he pored over copies of National Geographic and books about Ancient Egypt that his family – particularly his older sister – would gift him every Christmas. So it seems only natural that he would pursue a career in archaeology that’s taken him around the world, from teaching at the universities of Oxford and Cambridge in the UK to directing field projects in Africa and Asia that have reframed our understanding of ancient human migration. Professor Petraglia is now the Director of Griffith University’s Australian Research Centre for Human Evolution (ARCHE), and he talked to Griffith Review Editor Carody Culver about the origin story of our species – which, like humanity itself, is constantly evolving.
CARODY CULVER: Archaeology is one of those professions that’s quite sensationalised and romanticised – films like Indiana Jones really emphasise the intrigue and the adventure and don’t so much touch on the more practical, technical or scientific elements of the job. Could you talk a little bit about the multidisciplinary nature of archaeology and the different fields it draws on to help us study and understand the past?
MICHAEL PETRAGLIA: Discovery is what the public often sees – it’s the fodder of news and media attention that brings people into archaeology. It’s why I enjoy going to the field – as we discover new things and create new knowledge. But you’re right in that modern archaeology is not just about discovering things. In any large-scale archaeological project you have archaeologists and researchers from all sorts of subdisciplines – so on my projects, for example, I have the scientific contributions of geneticists, palaeontologists, Earth scientists, rock art experts and people from fields within the sciences and the social sciences and humanities. And that’s because when you go out into the field, you’ll be excavating, finding new archaeological sites, and you will ultimately have to put them into biological, cultural and environmental context. Archaeologists alone can’t do that, so you have to have a broad scientific team to effectively tell the story of what humans were doing in certain spots and how we evolved. You can’t really understand our history and our evolution without including a wide range of scholars. The key challenge is: how do you effectively bring the team together in order to tell a collective story? That’s the hard part.
CC: When you were in graduate school in the United States, you were drawn to the teachings of Lewis Binford, who’s known as the father of ‘New Archaeology’. Could you explain what New Archaeology is and what influence Binford has had on the field?
MP: Binford’s work began in the 1960s – it was a reaction against traditional archaeology, which back then was very culture-historical – it was dominated by an approach that looked at how material culture changed over time. Lewis Binford came in and forcefully opined that we archaeologists needed to be doing a lot more than just that: we needed to understand the behaviour of people in the past, and we needed to put that information into ecological context, examining changes through time, our evolution and much more. This ended up being called the New Archaeology. This academic change can be seen as part of the social changes that were going on in the US in the 1960s – when there was a lot of turmoil and rethinking going on. Binford transformed our field from one that was culture-historical to one that was more behavioural and ecological in approach, examining how humans and societies change through time.
I was taken by Binford’s writings and influenced by other people who had formerly studied with him, so I went on to graduate school at the University of New Mexico, where he was based as a professor, to study under him. By the time I got into graduate school in the 1980s, the New Archaeology was very much part of the fabric of what we were doing in our discipline.
CC: You’ve worked on large-scale projects across the world, and some of the work you’ve done indicates the ways in which climatic change has influenced humanity over hundreds and thousands of years. Could you talk a little bit about this, particularly in the context of the ‘out of Africa’ theory of human evolution, which has been challenged in recent years?
MP: We used to have a consensus in our field, in human evolutionary studies, that the origin of Homo sapiens was in Africa, with a speciation starting about 200,000 years ago – and there was only one early migration out of Africa, into the Levant, about 120,000 years ago. That date was supposedly the only out of Africa exodus. The consensus was drawn from the fact that there were human fossils in Israel that dated to between 120,000 years ago and 80,000 years ago. This indicated that humans made it out of Africa, but the consensus was that they failed to migrate more widely, ultimately disappearing, and that it wasn’t until 60,000 years ago that humans finally got out of Africa in one single wave to populate the rest of Eurasia. It was argued that humans finally got into Western Europe 45,000 years ago and down into Australia around 50,000 years ago. That’s the story that was retold for a long time in the literature.
I was working in India [in the 1990s] and was interested in looking for this single 60,000-year-old out of Africa wave. When I started the project, I had some archaeological sites in mind to examine that were supposedly representative of this migration, but when I investigated and dated them, they turned out to be very young. That was an odd result – and as I searched more for this wave out of Africa, I did not find it. What I ended up finding in India was that the so-called failed dispersal in the Levant was in fact part of a much wider wave of human dispersals across Asia and at an early date, prior to 60,000 years ago. I published a Science paper along these lines and it created a large controversy as our argument was that people reached India before 75,000 years ago.
Back then there wasn’t a lot of evidence to support that proposition, and so I stuck my neck out at the time. Many years later, I feel vindicated because more support has come from archaeology and fossil finds. So that was my beginning in this research area, arguing for multiple waves out of Africa, and not just a single, late migration. At the time I thought, well, how am I going to prove this? My thinking then was that if people were coming out of Africa, they must have crossed Arabia. So I embarked on a very large project in Arabia that continues to this day, addressing that very question: was there one wave or were there multiple waves out of Africa? To make a very long story short, we’ve found what we believe are multiple human dispersals out of Africa, paralleling the evidence found in the Levant.
This interdisciplinary archaeological work has contributed to the idea that our evolution is much more complex with respect to out of Africa migrations, but also concerning the ancestors that we may have met in our travels. Eurasia wasn’t an empty continent when humans dispersed out of Africa – it was occupied by Neanderthals and other species such as the Denisovans – and guess what? These species are represented in our DNA today. As we dispersed across Eurasia, we not only interacted with other human species culturally, we also mated with them.
CC: What role have fossil and genome studies played in the shift from that previous one-wave theory to this much more complex understanding of those multiple waves?
MP: DNA has been revolutionary, transforming our understanding of human evolution and our dispersal around the world. It has provided the evidence about the biological interactions that I was just referring to – archaeology in itself would not have shown that. There were some hints of those biological interactions among species in the fossil record as the morphology of the offspring of Homo sapiens and Neanderthals was slightly different. But the DNA proved it without a doubt. The evidence for species interactions has transformed our views about us and how we evolved – and it has also changed our perceptions about the Neanderthals.
CC: And what about climatic changes – how have they shaped these movements?
MP: Climate change is a huge part of our evolutionary story. For example, in considering the migrations of humans, one would assume that the Sahara and Arabia played a pivotal role. But if you look at a map of those places today, you might see those big deserts as barriers to migration. Indeed, if you’re thinking about the movement of humans between Africa and Asia, you might wonder: how could populations have crossed those arid zones? That’s the very reason that I went to Arabia, to examine the context of human migrations – and in fact we eventually found them. The main point here is that human migrations were attached to humid periods, not arid periods. The Sahara and Arabia have been going through cyclical arid and humid periods over hundreds of thousands of years. The Sahara and the Arabia that we see and know today are not the Sahara and Arabia of the past. Our work has shown that Arabia, for example, was full of rivers and lakes. We’ve now counted 10,000 ancient paleo-lakes in Arabia based on satellite imagery. We’ve visited about 200 or 300 of them, and surveyed them, and we’ve found fossils or archaeology on 70 per cent of the ancient lake edges. When you had a humid ‘green Arabia’, with savannas and grasslands and an extensive network of rivers and lakes, it opened up the arid barrier to migration. A humid Arabia allowed in human populations. It also allowed animals, such as elephants and hippos, to disperse. Hunter-gatherers would have followed these animals as they wandered, providing an explanation as to how people got out of Africa.
This cycle of aridity and humidity acted as an engine in the evolutionary process. At times, you have barriers to migration and at other times, you have new opportunities for migration: aridity, humidity, aridity, humidity – expansions, contractions, expansions, contractions. It’s like a pump. And that pump has huge evolutionary effects.
CC: So archaeology can help tell us the overarching story of humanity – how we migrated, how we evolved as a species – but as you’ve touched on, it can also tell us important and fascinating things about our behaviour and social histories. Are there any specific discoveries you can think of that illuminate some of these social and behavioural aspects of our existence?
MP: Sociality is a fundamental topic to look at in terms of our evolution, but it’s also a hard thing for archaeologists to grapple with because it’s difficult to interpret from artefacts and finds. Indeed, our social relations are hard to interpret based on the kinds of things that are preserved in the archaeological record – often we’re only left with stone tools or scraps of bone, and so you’ve got to infer what was going on behaviourally and socially. So there are some inherent difficulties in making interpretations, though our discipline is intuitively trying to address this.
Based on archaeological findings, we have a sense that social networks increased during the period when Homo sapiens was living in Africa as well as outside of Africa. Social networking between groups was probably one of the reasons why we were so successful in our worldwide domination. No other hominin species has ever occupied all parts of the Earth – so you naturally have to ask, why not? If you’re in a situation that is high risk – when your environment is changing, for example – you can lean on the next group over to try to work through some of those risks that you’re experiencing. Prior to Homo sapiens, populations might have just moved on or gone extinct in the face of environmental risks, whereas with Homo sapiens we were able to disperse widely across the world despite great ecological challenges. The underlying reason for that may be rooted in our social relations, our high level of co-operation – we don’t necessarily see that with earlier human species.
One of the things that’s clear in the human evolutionary story is that brain size has generally increased over time. Neanderthals and Homo sapiens have the largest brain sizes – so one has to ask, what’s the selective force behind that? As we see in other non-human species, greater sociality is connected to larger brain sizes. If you select for larger and larger brains through time, you also have increased levels of cognitive intelligence. This allows for increased levels of planning and prediction further into the future, with greater levels of consciousness and greater levels of understanding of individuals within society. This may help to explain and understand our own evolution.
CC: You recently became the director of Griffith University’s Australian Research Centre for Human Evolution (ARCHE). Can you tell me about the work the centre does and the contribution its researchers are making to our understanding of humanity’s origin story?
MP: I was really happy to come to ARCHE as it has an established, multidisciplinary group. We have geneticists, palaeontologists, archaeologists, biological anthropologists, geochronologists and rock art experts – we’re multifaceted. So, ARCHE is a centre with a great group of people in many subdisciplines that are needed to tell our evolutionary story. ARCHE has many research projects that are making an impact in our field and I can share a few recent examples.
One example is Jayne Wilkins’ work in the Kalahari in South Africa, which is similar to my work in Arabia – it’s looking at the arid zones in the Kalahari. We used to think people could not sustain themselves in the Kalahari over long periods, or they couldn’t adapt to environmental challenges. Jayne’s work is nicely demonstrating that, as in the Sahara and in Arabia, people were living in the Kalahari during humid periods but, most interestingly, populations were also adapting to the arid environment, and in those arid ecosystems they were able to eke out a living.
Something entirely different is the exemplary work being done by Maxime Aubert, Adam Brumm and Tim Maloney in Borneo. Their team found a skeleton [dated] at about 31,000 years old, which had evidence for an amputation of that individual. Why is that important? Well, 31,000 years ago people were living a hunting-and-gathering lifestyle, so they were mobile peoples. So the question naturally arises: how could a person with an amputated foot be living in a highly mobile community? Here’s where that inference of sociality comes in. The answer must be that they were taken care of by other members of the group. This evidence provides us with information about medical history as well as about people’s behaviour and social relations, their level of societal co-operation.
With respect to Australia, a recent publication and news story comes from Paul Taçon and Andrea Jalandoni, who are working with Traditional Owners in Queensland on an extraordinary rock art site. With knowledge provided by Traditional Owners, this rock art site is being documented in great detail, revealing the presence of all sorts of interesting images: snake-like creatures, people with six-toed feet, images of stars. The publication describes the relations between creation stories and what is preserved in the rock art – the Seven Sisters [Dreamtime] story. This research represents a beautiful blending of archaeology and ethnography in partnership with Traditional Owners.
CC: I read a great quote in the New Scientist by Robert Foley, a paleoanthropologist at the University of Cambridge. He said this at the start of a conference on human evolution in 2019: ‘What I’m sure of is that by the end of the first day something like 20 per cent of what I say will be wrong, by the end of the second day something like 50 per cent will be wrong, and at the end of the conference I’m hoping that something I said at the beginning still holds true.’ In an archaeological context, how important is it to be able to question and revise what you think you know?
MP: In our field, transformation of knowledge is happening every day, every year and every decade. Staying on top of that knowledge transformation, especially in the multidisciplinary arena, is very difficult. What I have taught has changed so much even in the last decade. That’s because there are always new discoveries in the field and in the lab leading to the growth of new knowledge. Rob’s quote is absolutely valid and, on the positive side, it means that we’re learning, we’re building new knowledge and we are addressing research gaps. When we address those gaps and start to close them, we create new knowledge, but that in turn opens up more gaps in our knowledge. As scientists we’re building towards greater understanding but this is a never-ending process. It’s obvious that we’re obtaining more and more accurate information through time, building towards that ultimate truth that we seek, but will never truly actualise. From a practical perspective, and as an example, I’m so proud of the research that we have done in Arabia, but I can foresee many decades of research long after I’m dead and gone.
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