Why Did Civilization Rise in the Holocene and Not the Eemian Epoch?
Scientists have been arguing for over a decade about the validity of comparing climate changes in the current geological period (the Holocene-Anthropocene epochs) with climate changes in the Eemian epoch, which lasted from about 130,000 years ago to about 115,000 years ago. The Eemian (also known as the Sangamonian, Ipswichian, Mikulin, Kaydaky, Valdivia, or Riss-Würm epoch) experienced a warmth similar to that of the Holocene epoch, which began about 11,700 years ago. These comparative models are used to predict where current global warming trends may lead.
Global Warming is A Natural Phenomenon
Geologically speaking, global warming (and climate change) are nothing new. The Earth has experienced alternating periods of cold and warmth for billions of years, and the climate is constantly changing as the sun grows warmer, as the biosphere alters the chemical composition of the atmosphere and the oceans, as the Earth’s orbit gradually changes, as the Earth’s spinning motion gradually slows down, and for many other reasons. In fact, climate change is a self-sustaining dynamic; each change in the climate contributes to the next change in the climate.
Earth’s climate “breathes” on a very slow, gradual scale that is imperceptible to human experience, but in a way that is very visible in the data that we collect. We know that climate change is occurring all the time, and we have known this for over 100 years. The political debate over climate change has more to do with how much mankind is influencing the climate through industrial and technological activity. Political recognition of human influence on the climate change process entails accepting responsibility for making changes in how humans interact with the environment.
In the United States political conservatives barely recognize that air pollution is a problem. They are reluctant to admit that rising ocean levels and changing weather patterns are being driven by the melting of polar and glacier ice. The ice melts are changing the chemical makeup of the Earth’s oceans and altering water temperatures. These changes are affecting everything from the jet stream to where rain clouds form.
The warming climate will grow warmer even if mankind stops burning fossil fuels, cutting down forests, and sucking fresh water out of river systems. We cannot halt the process but we do appear to be accelerating it. But enough about politics and the climate. All we need to understand for this discussion is that mankind has done something in the Holocene-Anthropocene interglacial that we did not do in the Eemian: we have changed the climate.
There was No Human Civilization in the Eemian
We have discovered many fossils and relics from the Eemian. We know that our ancestors were using sophisticated stone tools, traveling great distances, even crossing water, and exchanging valuable goods with each other as much as 120,000 years ago. But nowhere during the 15,000 years of the Eemian interglacial period did agriculture or animal husbandry arise.
It was mankind’s domestication of plants and animals that made civilization possible, or so we believe. Of course, there are other things that contributed to civilization’s rise. For example, people had to learn how to construct durable shelters and how to manage natural resources in an area. Our understanding of how much of these things humans living during the Eemian period possessed is limited by our ability to find traces of their lives in the dirt. We have much more archaeological evidence about humanity’s progress over the past 50-60,000 years.
And in the past decade or two we have supplemented our archaeological knowledge with DNA analysis of both human and non-human species. All of the data we have collected so far points to civilization arising only after the Earth began warming again nearly 12,000 years ago. So far we have found no evidence of large, long-term communities from the Eemian period. It would be a remarkable discovery, and one that opens science to a whole new world of exploration, if we could find even one permanent village from 120,000 years ago. But scientists are not holding out much hope for such a discovery.
The record so far lacks any trace of a pre-Holocene civilization.
But Human Advances Began Earlier Than Previously Believed
One of the great mysteries of science is when our ancestors first domesticated dogs, and why. Up until recently the domestication of dogs was believed to have occurred within the Holocene itself, and that it may have contributed to the rise of Neolithic cultures (the precursors of the earliest civilizations). Neolithic cultures marked the onset of permanent and semi-permanent habitations. They coincided with the introduction of agriculture and animal husbandry, or so we have thought until now.
One recent DNA study suggests that dogs separated from wolves somewhere between 27,000 to 40,000 years ago. That pushes dog domestication back into the Pleistocene, indeed into the last glacial period (known as the Wisconsinan, Weichselian, Devensian, Llanquihue, or Otiran glacial period). That glacial period lasted from about 115,000 years ago to about 12,000 years ago. In other words, we traded 15,000 years of warm climate for 100,000 years of cold climate.
If we assume that dog domestication occurred around 40,000 years ago that would be about 30,000 years after the Toba Event, a massive supervolcanic eruption that made the Earth even colder and which almost led to the extinction of the human race (and many other species). The Toba Event might have played a role in the rise of civilization, but we’ll come back to that later.
In addition to domesticating dogs, modern humans reached Europe around 45,000 years ago. Neanderthals vanished from Europe over the next 10,000 years. Denisovans, another human species about as closely related to us as the Neanderthals, also vanished from Asia in the same time period. Did dogs give our ancestors an advantage over Neanderthals and Denisovans? Maybe. But we can also be sure that our ancestors interbred with the other humans on Earth; we have inherited some of their DNA.
But something else happened prior to 12,000 years ago. Humans in the Middle East began domesticating plants around 23,000 years ago. This recent discovery is forcing us to change how we think civilization began, because in order to domesticate plants people have to claim territory; they have to hold it in a way that wandering hunter-gatherers do not.
A six-shelter “camp” near the shore of the Sea Galilee has produced remnants of 150,000 plants, including many weeds that would only be present in an area where other plants are cultivated, has proven that modern humans were tending plants 23,000 years ago. This is not a farming village. It is more like a semi-permanent encampment with gardens. Designated the Ohalo II People, these hunter-gatherers also sustained themselves on fish in their sedentary lifestyle. This early clan raised 140 plants, including cereals like wild emmer, barley, and oats.
And this camp was not the birthplace of cultivation. We don’t yet know where modern humans first began to raise wild crops. Other sites may be discovered in the years to come.
When Did We Begin to Build Cities?
Gobekli Tepe is the oldest known human town, but we know that human culture evolved over many thousands of years. The founders of Gobekli Tepe brought skills and knowledge with them, just as the clan who built the camp by the Sea of Galilee brought skills and knowledge with them. We don’t know when the first permanent settlement was made, when the first successful attempt at raising a crop of wild plants occurred, or why people chose to live this way.
All we know is that there is a long road from the Sea of Galilee Circa 21,000 BCE to southeastern Anatolia (Turkey) Circa 9100 BCE. Gobekli Tepe is not a city but it is more than the mere temple that some people have made it out to be. In fact, the ritualistic interpretations of Gobekli Tepe’s purpose are completely nonsensical unless one posits an extremely advanced sedentary society existing around the site (in towns or villages that have yet to be discovered).
Archaeology has shown that large “ritualistic centers” such as Stonehenge did not exist by themselves. The people who used these sites for whatever purposes in fact lived near them in dwellings that have been at least documented if not fully excavated.
Whatever the purpose of ancient sites like Gobekli Tepe, they were built and used by people who had to eat and sleep and who dwelt within walking distance of the sites. “Walking distance” can be measured in hundreds of miles but the larger communities would have to dwell close by at least part of the year, and in most cases we eventually learn that large archaeological sites were settlements. The houses are usually buried outside the great structures but still close by.
The existence of Gobekli Tepe, dating from almost the very edge of the Holocene-Pleistocene boundary, tells us that modern humans had been building in stone for quite some time, possibly thousands of years, by the time they cut the first bedrock at Gobekli Tepe. Although not as structurally sophisticated as architecture that was built thousands of years later, Gobekli Tepe does not represent a first generation project. It was planned and built with skill and tools.
The “stone town barrier”, the time when the very first permanent human settlement like Gobekli Tepe was founded, may lie much farther back in time, but we can say with great confidence that it would be somewhere between 12,000 and 23,000 years ago.
Why Did We Begin to Build Cities?
To understand why our ancestors began to build larger communities than family groups required to survive we’ll have to learn much more about the world in which they lived. What we know so far is that the period from 23,000 to 12,000 years ago was a time of great transitions. Modern humans migrated across Asia into North America. The glaciers began to melt and sea levels rose. The ancestors of modern Berbers migrated to what is now Tunisia around 20,000 years ago. Within a few thousand years one last cold phase brought the glacial period to an end and true warming began.
We don’t know exactly when modern humans began hunting large game like mammoths but they were going extinct by the end of the Pleistocene, probably due more to climate change than to human hunting. It is doubtful that mammoths ever comprised a substantial part of the modern human diet in areas that gave rise to agriculture and domestication of animals. The theory that dogs may have been bred by mammoth hunters in Asia who captured wolf pups is intriguing but requires more study. We think humans were hunting mammoths as much as 1 million years ago, so why would they start sharing the hunt with wolves around 30,000 years ago?
Something changed significantly enough to compel modern humans to form relationships with dogs, to begin the systematic cultivation of plants, and to learn how to build large permanent settlements. It may be that our theories of human expansion from southeast Africa after the Toba Event (around 70,000 years ago) explain what happened: a population explosion. As few as ten thousand modern humans survived the cooling after the Toba Event, almost certainly because they lived in Africa. But how many Neanderthals and Denisovans survived?
For more than 100 years scientists believed that Neanderthals had evolved to survive in cold climates, but that makes little sense given the immense time scale of their history. Recent research also suggests that many of the features once believed to indicate cold climate adaptation have no such significance. In other words, Neanderthals (and likely Denisovans) were probably no better adapted to the cold climate than we are.
So if the Toba Event triggered a decline among all large mammal species we can look for signs that modern humans collaborated better with other species than other humans. Neanderthals and Denisovans may have survived longer thanks to modern humans and dogs, not in spite of them. Cultural experimentation could be a direct result of surviving the Toba Event. Maybe modern humans had to develop an entirely new way of working together because pre-Toba food sources began vanishing. Modern humans began leaving Africa around 60,000 years ago.
A dearth of reliable food sources might explain the rapid expansion from Africa. Instead of competing for dwindling resources families may have undertaken the decision to go look for new resources. The families that stayed behind eventually learned new survival skills. Moving into new lands would have challenged the migratory families to find new sources of food. However, if there were other humans already present in newly discovered lands then learning how Neanderthals and Denisovans survived would have given the wandering Homo sapiens an advantage.
And yet at some point whatever they could do for themselves, whatever they gained by cooperating with dogs and perhaps other humans groups was not enough. Modern humans began experimenting with the cultivation of plants. They may also have begun experimenting with animals in ways we have yet to determine.
There is, in fact, a very recent example that illustrates how our ideas about domestication can be completely wrong. For generations scientists and teachers have taught us that horses were first domesticated about 5,500 years ago. Now new research shows that horses were domesticated on the Arabian peninsula about 9,000 years ago.
Ruling Out the Eemian Paradox
But if we can attribute the development of these new food and sheltering skills to climate change, why did they happen after the Eemian and not during or before? New research suggests that the Eemian epoch did not proceed as smoothly as the Holocene in terms of warming the Earth. It will take years to assess the implications of this new data, but we now know that Earth’s climate during the Eemian was not as similar to the Holocene’s climate as previously supposed. The climactic differences may have been enough to preserve the food chain across the ecosystem in a status quo that did not demand significant change.
In other words, climactic changes prior to the Toba Event may have been gradual enough that the ecosystem was able to adapt without substantial loss of species. But after the Toba Event things become less certain. In fact, new data suggests that the Arctic regions cooled more than previously believed over the past few thousand years, and that as the Earth warms up current climate models may underestimate just how much warmer things will get.
What we see over the last 70,000 years is a pattern of climactic shock. The anomalous three Dryas periods that interrupted the gradual warming of the Earth which began around 22,000 years ago are perfect examples of climactic shock. We do not know why they occurred but we know that they coincided with periods of great ecological and cultural change from which the Earth’s ancient ecosystem never recovered.
The three cool Dryas periods occurred from about 18,000 years ago to about 11,500 years ago (ranging over 6,500 years). Another climactic shock designated the 8.2ka Event occurred around 8,200 years ago. And very recent research now suggests that the area of northwest Iran was dry prior to 9,000 years ago and after 6,000 years ago, allowing for a 3,000-year wet-and-warm period.
The frequent and rapid fluctuations in global climate that began around 22,000 years ago are not replicated in our Eemian data. This is not conclusive proof that the Eemian did not experience similar climactic shocks but we already have data to show that the Eemian period did not proceed in the same way the Holocene did. Furthermore a recent study in the application of Dynamic Systems Theory to the archaeological record of where and how early agriculture and domestication occurred suggests that sudden changes in resource availability may have contributed to the rise of civilizations around the world.