Science Blog

Central Asia: A Key Region for Our Ancient Relatives

Stalagmite photo1

Dr. Finestone publishes new research in PLOS One.

Humans are incredibly widespread geographically. We live on all continents and virtually every corner of land on Earth, something no other large mammal is known to do. Crucial to our ability to migrate to new environments is the capacity to make and modify tools to overcome environmental challenges. This began millions of years ago, when members of the human family tree (called hominins) first began to make stone tools. Our ancient hominin relatives took these tools with them as they dispersed across Africa and out into Europe and Asia.
 
Central Asia is positioned at the crossroads of several important areas for hominin dispersal, linking east and north Asia with Europe and west Asia. It acted as a gateway between several zones where different species of ancient hominins lived and may have interacted with one another. We find clues about the ancient hominins who lived there from fossilized skeletal remains and the stone tools they left behind. However, most of the archaeological evidence from Central Asia lacks context for dating and/or environmental reconstruction. Additionally, the modern climate of the Central Asia interior is extremely arid and water sources are scarce. In the past, this may have posed a variety of environmental challenges that led some scientists to conclude that much of Central Asia was inhospitable to our hominin ancestors.

IN SEARCH OF NEW EVIDENCE

How are stone tools and fossils preserved in the earth for researchers to find thousands or sometimes millions of years later? This process is complicated—especially for fossils—but the basics rely on sediment accumulation and burial. However, in the plains of Central Asia, erosion now outpaces sediment accumulation. Stone tools are found deflated on the surface and the primary sediments that buried them have long eroded. This is a problem for archaeologists because primary sediments contain key information about the age and local environment that existed when objects were discarded. As a result, our knowledge of hominin activity in the Central Asian lowlands is disproportionately limited compared to other regions and many questions remain unanswered. How can we reconstruct past behavior when the context is missing?

Approaching a problem of this scale requires a team. In our case, this included a diverse group of archaeologists and paleo-climatologists from institutions that spanned four continents. First, we compiled a dataset of 132 Paleolithic sites across Central Asia—the largest dataset of its kind. Although the majority of these sites lacked dates and context, the database allowed us to look for patterns in the location of findings and types of toolkits. Next, we analyzed a mineral deposit (called a stalagmite) that formed over a 780-year-long period in a cave in southern Uzbekistan. As the stalagmite grew, its composition reflected the local and regional environmental conditions of the area. We cross-sectioned the stalagmite, drilled samples, and measured the amount of different elements present during its growth interval. This allowed us to date and reconstruct the timeline of growth and learn about local climate and hydrology during this interval at unprecedented temporal resolution. When coupled with the archaeological data, we could consider the distribution of Paleolithic sites in the context of a high-resolution climate record. We can learn what kind of seasonality early hominins experienced in the past. (Picture: cross-section of stalagmite)

CENTRAL ASIA: A KEY REGION FOR HOMININ MIGRATION?

We learned that the stalagmite in this study grew at the end of the Marine Isotope Stage 11 (a warm period between glacials) around 400,000 years ago. During this time regional climate was not characterized by simple (slower) trends toward cooler or dryer conditions, as long-term climate records would suggest. The short-term record varied, with periodic warmer and wetter conditions punctuated by drying events that lasted for decades. When regional warmer and wetter intervals coincided with warm periods between glacials, this could have supported hominin expansion into vast areas of the Central Asia interior. 
 
The patterning of tool assemblages also reflected this. We found that assemblages with bifaces (stone tools that hominins worked on both sides) occurred across arid zones at higher latitudes and in lower altitudes relative to the other assemblages. In Asia, bifaces have previously been linked to the Middle Pleistocene (an era ~700,000–100,000 years ago) and the highly successful hominin species Homo erectus. Together, this supports that the local environment of arid Central Asia was sometimes a favorable habitat for Middle Pleistocene hominins and an important zone of dispersal for toolmakers producing bifaces.

TOWARD THE FUTURE

Our lineage’s history was formed in the balance of changing climates and the cultures harnessed to survive new conditions. In Central Asia, it seems that favorable conditions and diverse toolkits aligned periodically during the Middle Pleistocene, allowing our ancient relatives to inhabit and disperse across the region. Interdisciplinary research bridging archaeology with paleoclimate models are becoming increasingly necessary for understanding human origins—and the interface between environment and culture is still at the center of our species’ role in the natural world today. In the future, the databases generated from this study will continue to allow us to ask questions about the context of hominin dispersals and the unique environmental challenges that our ancestors overcame. 

Click here to view Dr. Finestone's full article, "Paleolithic occupation of arid Central Asia in the Middle Pleistocene."