Picture an endangered species forced by the environment to retreat to a small refuge. Its population has dwindled to thousands or fewer, and its survival is uncertain. This grim scenario may have already happened - to us.
What's more, humans not only survived a population crash, but also emerged with complex behaviors allowing us to mold our surroundings to suit us, rather than the other way around. We became 'modern,' able to live in virtually any earthly environment.
"What are the evolutionary contexts for the spectacular levels of complexity in humans enabling us to cooperate with non-kin,"asks Curtis Marean, professor in the School of Human Evolution and Social Change at Arizona State University (ASU) in Tucson, US. "When and why did they arise?"
To answer these questions, ASU researchers and colleagues in South Africa, Australia, Israel, and France studied the archeology of the Cape Floral region of South Africa. They believe this region may be where humans rose from near-extinction to global domination.
Evidence in the ground and in our genes
Human interrelatedness tells us everyone on Earth today may descend from about 15,000 survivors of a population crash. Based on genetic mutation rates, this crash happened between 100,000 and 300,000 years ago.
A long dry phase during the Last Glacial Maximum (LGM) could explain why our population crashed. The Cape Floral region of Africa is one of the few areas on the continent to show evidence of human habitation from that time. It is also at this time humans began displaying behaviors differentiating 'modern' from 'early' humans, such as complex thermal treatments of stone to make better tools, or carving geometric patterns in ochre and bone.
"It seems very likely that modern human lineage evolved during a glacial stage when Africa was mostly dry and uninhabitable," Marean says. "Our big brain is wired to allow us to think in complex analogies, plan for the future, understand mathematics. If we're trying to understand the cognitive genetic encoding leading to modern humans, we need to understand the environment at that time."
Blacklight provides key insights
One archeological finding caught Marean's eye. Cape Floral is rich in shellfish and tubers, a combination of foods that would certainly have satisfied our need for protein and carbohydrates. But were they abundant and available enough to sustain the human remnant at the time?
"Our project began as a straight archeological dig, looking for evidence of modern human behavior," notes Marean. "Then I realized that we needed much better climate and environmental contextual data to understand the archaeological record we were excavating."
After a few years of working on desktop computers, the Arizona State researchers decided to "up the ante" by taking their models to Blacklight at the Pittsburgh Supercomputing Center in Pennsylvania, US. With 4,096 cores and up to 16 terabytes of memory available per job, Blacklight is serving the memory and processing requirements for two simulations.
The first simulation is a paleoclimate model to assess how currents and wind movements during the LGM may have affected the local climate in the Cape Floral region. The second will be an agent-based model that simulates plants, animals, and humans in a realistic way.
Thanks to Blacklight and support from PSC staff, the paleoclimate model is the first simulation of the Cape Floral region during that period to shed light on whether the area was warm and wet enough to sustain sufficient shellfish and tuber populations - a major accomplishment in the field. Even better, initial results suggest that the climate would indeed have supported the food sources humans needed, at a time when virtually no other place in Africa did.
Next, the scientists will run the agent-based model and explore the role of this environment in the emergence of modern behaviors. The project promises enough predictive power for archaeological evidence and the models to be tested against each other - another first.
"We have debates over exactly how small the modern human population was at this point. Some argue that the progenitor population was in North Africa, or the Maghreb area," Marean says. " It's going to be a while before we can say one way or another, but I think right now the Cape Floral region hypothesis is a strong one. And like all good hypotheses, it's generating an enormous amount of good science."
