When humans first set foot in Australia more than 65,000 years ago, they were faced with the dangerous task of navigating a country they had never seen. Now, scientists have used supercomputers to simulate 125 billion possible itineraries and reconstruct the most likely “superways” that these ancient immigrants used as they spread across the continent. The project provides new insights into how landmarks and water she supplies to human migrations, and gives archaeologists clues as to where to look for undiscovered ancient settlements.
“This is a really compelling illustration of the strength of using these [simulation] techniques, on a huge, continental scale to understand how people navigate on land, ”says archaeologist Kyle Bocinsky of the University of Montana, Missoula. “It’s impressive, extreme computing.”
Scientists have long wondered about the routes that humans first took to Sahul, the landmass that connected Australia, New Guinea and Tasmania, before the islands were separated by rising seas about 20,000 years ago. Most scientists believe that ancient people used boats to cross from Asia. But the routes they took when they reached land have never been obvious.
To reconstruct the potential paths of early travelers, scientists collected the first detailed topographic m of the Sahul – including former coastal areas now underwater – from satellite, aerial and subsea mapping data. Next, they turned to a computational technique called cheapest path analysis to calculate optimal hiking routes across this recreated landscape. The calculations are analogous to pouring digital water on a virtual land and seeing where it flows, following the paths of least resistance.
In this case, the researchers created an imaginary traveler – a 25-year-old woman carrying 10kg of supplies – and sent her on billions of journeys across the Sahul. Their simulation calculated how many calories she would have burned while walking each route, as well as which trails would have provided a reliable water supply based on what they knew about the lakes, rivers and springs that existed in Australia at the time. The team also simulated what the traveler would have seen as she walked, noting prominent landmarks – such as rugged protrusions or prominent ridges – that she might have used as navigational aids.
It took weeks to run the complex simulations on a supercomputer powered by the US government, says co-author Devin White, an archaeologist at the US Department of Energy’s Sandia National Laboratories who developed several of the computational problems. “We took time at night and on the weekends,” he recalls. But the number crunchy revealed in the end a network of “optimal highways” which had the most attractive combinations of easy walking distance, water and landmarks, the researchers reported last week in Nature Human behavior.
Optimal path in hand The researchers faced a fundamental question, says lead author Stefani Crabtree, an archaeologist at Utah State University, Logan and the Santa Fe Institute: Was there any evidence that real people had once used these computer-identified corridors? To find out, the researchers compared their routes with the location of the approximately three dozen archeological sites in Australia that are known to be at least 35,000 years old. Many places sat on or near highways. Some corridors also coincided with ancient trade routes known from native oral histories or adapted genetic and linguistic studies that were used to trace early human migrations. “I think we were all amazed at the goodness of the fit,” said archaeologist Sean Ulm of James Cook University, Cairns.
M has also highlighted little-studied migration corridors that could provide future archaeological discoveries. For example, some early superways sat on coastal areas that are now submerged, giving marine scientists a guide to exploration. Even more exciting, say the authors and others, are important routes that run through several arid areas in central Australia and in the northeast of Queensland. These trails challenge a “long-held view that the earliest humans escaped the desert,” Ulm says. The Queensland Highway in particular presents “an excellent focal point” for future archaeological research, says archaeologist Shimona Kealy of the Australian National University.
Bocinsky hopes other researchers will use the technique to undertake early migration routes across other continents, including North America. But he admits that “it will not be easy for anyone to replicate … if they do not have a supercomputer.” If they do, they could gain more than just an understanding of human migrations from the past. The muscular digital tool, White says, can help researchers understand how future migrants can escape problems like war and global warming. “There’s a lot of potential here.”