TWH – Climate change has happened before. When it did, it threatened access to resources. It may have spurred human evolution. Examining past climate change may tell us something about our likely future.
Two recent studies discuss the impact of past climate change. In one study, the authors examine the effects of rising sea levels on a part of Spain’s Mediterranean coast. The other study discusses how climate change in the Pleistocene drove human evolution.
A brief refresher on pre-history
The Paleolithic Age had a much more turbulent climate. Geologists call this period the Pleistocene Epoch. It began 2.58 million years Before the Present (B.P.). It lasted to roughly 12,000 B.P., roughly 10,000 B.C.E.
Maximum glaciation of the northern hemisphere (shown in black) during the Quaternary climatic cycles Ice coverage – Image credit: Hannes Grobe/AWI – CC BY 3.0
During that period, glaciers advanced and retreated more than once. It is often referred to as “the Ice Ages.” An unknown number of hominin species including homo sapiens (modern humans) evolved and lived during this period. Hominins refer to species of bipedal, primate mammals that walk upright. Hominins include modern humans and Neanderthals among others. In the Paleolithic, all hominin species could only hunt and gather the resources they needed.
The Mesolithic was a transition period between the Paleolithic and the Neolithic. Global natural events defined the beginning and end of the Pleistocene. In contrast, technological and cultural changes among humans define the beginning and end of the Neolithic. The start of the Neolithic varied by region and by culture. No global, universal date for the beginning of the Neolithic exists.
Around 12,000 years B.P., the climate began to stabilize. In the Fertile Crescent (Iraq, southern Turkey, and Syria), people began to domesticate crops and animals. In other places, humans domesticated different crops and animals. Anthropologists have defined this cluster of inventions as the “Neolithic tool kit.” It did so in the context of a relatively stable climate. All human history has occurred in this period of this relatively stable climate. Geologists call this era the Holocene Epoch.
In pre-history, evidence is sparse and suffers from survival and availability bias. Scientists have studied Europe and the Middle East much more than the rest of the world. All dates are rough approximations.
Climate change in Mesolithic-Neolithic Spain
In a “Journal of Maps” article, its authors reported on the sea-level rise along part of Spain’s Mediterranean coast.
Map of global sea levels during the last ice age -Image credit: National Oceanic and Atmospheric Administration – Public Domain
The authors of this study chose to focus on a narrow part of Spain’s central Mediterranean coast. In pre-history, two human communities existed in this region. In the Mesolithic Age (9830 to 8060 B.P. along the Spanish coast), humans lived in “El Collado.” In the early Neolithic period (7550-7320 B.P. along the Spanish coast), humans lived in “El Barranquet.” This coastal area also had a lagoon.
Prior researchers have found evidence for the locations of the shoreline and lagoon in 9000, 8800, 8500, 8100, and 7300 B.P. During most of this period, sea levels rose. Those rising sea levels flooded coastal areas and the lagoon. At the end of the period examined, the sea had moved 4 km (2.5 miles) of land. Data from these five dates allowed the authors to plot coastal changes over time
Resource availability
Humans need resources for food, water, clothing, shelter, adornment, and other necessities. Every settlement would need a nearby resource area for hunting and gathering these resources. The people from El Collado would have hunted and gathered those resources in nearby areas. No evidence exists for domesticated animals. That would mean they would have traveled by foot to hunt and gather.
Based on case studies and ethnographic literature, archaeologists can estimate the size of a settlement’s resource area. El Collado’s resource area would have to be within a two-hour walking distance. If that area shrank, loss of access to resources would threaten the settlement.
Archaeologists were able to take historical data for the location of the shoreline over time. Their software made a visual display showing how rising sea levels change the area. Archaeology Network News has posted a link to that video display.
What did people from El Collado eat?
After eating an animal, people discarded its bones in a midden, a “prehistoric garbage dump.” A midden’s remains provide archaeologists with a way to examine what people ate. In the nearby lowlands, people from El Collado hunted red deer and aurochs. The later, now extinct, were the wild ancestors of domesticated cattle. In the nearby hills, they hunted ibex and wild boar. From the sea and lagoon, they ate fish, mollusks, and Mediterranean cockles.
As sea levels rose, water covered more of the lowlands. The salt waters also began to flood the lagoon. Habitat for El Collado’s resources decreased. Animal remains show a decrease in foods from the lagoon and an increase in terrestrial foods. That would suggest that rising sea levels had more of an impact on the lagoon than on the lowlands.
By the time of the Neolithic, the sea had swallowed the lagoon. A major food resource for the people of El Collado had disappeared. Its people had abandoned El Collado.
Then, people with the Neolithic “tool kit” settled in El Barranquet. The people of El Barranquet practiced early agriculture and animal domestication.
El Barranquet had much less available land. The shoreline had moved far inland. The lagoon had disappeared. Studies of Neolithic settlement patterns provide a way to calculate a minimum Neolithic resource area.
Their use of the Neolithic tool kit allowed them to live within a resource area of a one-hour walk from their settlement. Their resource area would have been half the size of El Collado. The people of El Barranquet had adapted to a changed climate.
Climate change and speciation
Scientists studying human evolution believe that climate changes played a key role in species evolution among different hominin species.
Skulls at the Natural History Museum, England that range from homo habilis to homo sapiens – Image credit: Emőke Dénes – CC BY-SA 4.0
The journal Nature recently published an article about climate change in the past. Its authors used computer modeling to analyze climate changes over the last 2 million years. They also analyzed resource availability.
Next, they compared that data with data about five hominin species. Those five species include homo habilis, homo erectus, homo heidelbergensis, homo neanderthalensis, and homo sapiens.
The Pleistocene Epoch
The Pleistocene Epoch generally had a cold and dry climate. It was the time of the Ice Ages. Periodic warming separated each of the Ice Ages.
Those shifts between increasing cold and increasing warmth changed environments around the world. The changes would have caused a Darwinian natural selection process to occur.
Some random genetic mutation would have produced a new trait and one that might be better adapted to the new conditions. If so, people carrying that mutation would be more likely to survive and reproduce than those without it.
The mutation would then become more common in the gene pool. This process could eventually lead to the evolution of new species or speciation.
The authors of this study plotted the locations of the remains of each species. Then, they linked those locations to known climate factors in those areas. This allowed researchers to estimate the climatic conditions to which each species had adapted. It also allowed them to predict potential contact zones for inter-breeding among hominin species.
How different species adapted to different climates
Homo habilis (2.4 to 1.5 million years B.P.) had a limited range in eastern and southern Africa. They had adapted to a limited, specific climate and habitat. Changes to either would threaten this species.
In contrast, homo erectus (1.9 to 0.1 million years B.P.) had a much greater range of habitats in Africa and Eurasia. Anthropological evidence indicates that homo erectus was a “flexible generalist.” Homo erectus were wanderers that had adapted to multiple environments.
Homo heidelbergensis (600,000 to 200,000 B.P.) migrated out of Africa and into Eurasia. The study’s authors argue that climate variability drove them out of Africa. In those wanderings, they would have encountered many different climates. These new climates would have required adaptations. Their northern branch left Africa and evolved into Neanderthals. Their southern branch evolved into homo sapiens (modern humans).
Homo sapiens (315,000 B.P. to present) had greater suitability to dryer conditions than any of the four other species. This suitability for dry conditions may have helped many waves of our species across the Sinai to get to Eurasia.
Humans evolved to prefer drier conditions. The coming climate change promises to be warmer and wetter.
Ancient Rome depended on its aqueducts for their water. When the Germanic tribes attacked, they cut some of the aqueducts. Without the water from the aqueducts, Rome’s population had no water. Rome’s population dwindled.
Advanced countries depend on complex supply chains involving global shipping all over the world. Those networks depend on harbors. Complex supply chains are the aqueducts of the modern world.
In the last two and half years, the world has seen what disruptions to supply chains can do to modern, globalized trade. Rising sea levels threaten the harbors critical for global trade. The disruptions of the last two years are likely to seem minor in comparison.
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