A set of factors have been found that preceded population crashes in Europe thousands of years ago. If the peoples of the time had been aware of their significance, perhaps they could have taken evasive action. It's far too late for those long-gone cultures, but some of the same signs could be very relevant today.
The study of regime shifts has become a major component of ecology in recent decades. Such shifts are usually preceded by declining resilience, or the capacity to maintain the health of a system. The markers of declining ecological resilience have been extensively cataloged. The understanding developed from ecosystem research has been applied to other complex systems, including human society, but it has proven much harder to identify the early warning signals (EWSs) for social systems.
Dr Sean Downey of the University of Maryland may have changed that. He has developed a set of EWSs, and shown they occurred prior to at least seven population collapses in Europe between 4,000 and 8,000 years ago, an era known as the Neolithic.
Downey chose nine well-studied regions of Europe and used data from more than 2,000 archaeological sites, with over 13,000 individually dated items. Population changes over time were estimated from the ratio of newly founded villages to old abandoned ones. Each region saw relatively steady population growth over many centuries after the introduction of agriculture. Eventually, however, all nine suffered at least one crash, losing up to 60 percent of the population in the course of a century.
These collapses did not come out of nowhere, however, and seven of these regions met Downey's EWSs, while the other two were more ambiguous.
As populations grew, Neolithic Europeans started to over-exploit resources. Nomadic peoples faced with the same problems might have moved, but these early agricultural populations were deeply invested in their locations. They responded in ways that might have provided temporary respite, but made things worse in the long run. “Continuing on such unsustainable courses in the face of steady resource decline ultimately leads to catastrophic failure,” Downey and his co-authors write in Proceedings of the National Academy of Sciences.
One of Downey's study areas was the basin around what is now Paris. After agriculture was introduced to the region, it experienced more than 1,200 years of fairly steady growth. However, it has previously been found that 6,225 years ago, the population of the area experienced a sudden “bust”. Downey found evidence of warning signs appearing 6,800 and 6,300 years ago, respectively.
Along with sharp swings in population numbers, one of the major warning signs of collapse for these European Neolithic societies was deforestation. Considering the astonishing rates at which tropical rainforests are being felled, this is a disturbing indication that our future may reflect the worst aspects of our past. The difference is that this time we have the warning signs if we wish to act on them.