The Role of Mountainous Terrain in Early Human Evolution
Exploring How Diverse Mountain Ecosystems Shaped Hominin Adaptation
Mountainous regions have long attracted early human populations, but the reasons behind this preference are becoming clearer thanks to new research. A recent study published in Science Advances1 by scientists from the IBS Center for Climate Physics (ICCP) at Pusan National University reveals that the diverse ecosystems within these terrains played a crucial role in human evolution. This research highlights the importance of biodiversity and environmental variety in shaping early hominin adaptations.
The Attraction of Mountainous Regions for Early Hominins
Archaeological evidence shows that early hominins—members of the genus Homo—frequently settled in or near mountainous regions. To explore the factors influencing this pattern, the ICCP researchers analyzed a comprehensive dataset of hominin fossils and artifacts, paired with high-resolution landscape data and a 3-million-year-long climate simulation. The results suggest that these rugged environments were key to human evolution, shedding light on why early human species chose such challenging terrains.
Elke Zeller, a lead author of the study and a PhD student at the IBS Center for Climate Physics, stated,
"When we analyzed the environmental factors that controlled where human species lived, we were surprised to see that terrain steepness was standing out as the dominant one, even more than local climate factors, such as temperature and precipitation."
Diversity in Ecosystems and Its Evolutionary Impact
Mountainous landscapes, characterized by varied elevation, naturally support a range of environmental conditions. This diversity of ecosystems and vegetation types, known as biomes, creates hotspots for biodiversity. The study illustrates how this biome diversity provided early human populations with a broader range of food sources and increased their resilience to climate fluctuations. The concept, referred to as the Diversity Selection Hypothesis, suggests that early humans were attracted to these regions for their rich and varied resources.
The ICCP team's findings demonstrate that these diverse habitats, despite their navigational challenges, offered significant evolutionary benefits. By adapting to the steep and rugged terrain, early hominins were able to access a wealth of resources not available in flatter areas. Over time, these adaptations became critical in the development and survival of different hominin species.
Evolutionary Adaptations to Rugged Terrain
The study traces the evolutionary adaptations of early human species, such as Homo habilis, Homo ergaster, and Homo erectus, up to around one million years ago. During this period, these species showed signs of adapting to steep landscapes to exploit the diverse resources these regions offered. However, the evidence of this adaptation temporarily disappears about one million years ago and then re-emerges around 700,000 years ago with species like Homo heidelbergensis and Homo neanderthalensis. These later species, capable of fire control, demonstrated greater tolerance for colder and wetter climates.
Axel Timmermann, Director of the IBS Center for Climate Physics and co-author of the study, noted,
"The decrease in topographic adaptation around 1 million years ago roughly coincides with large-scale reorganizations in our climate system, known as the Mid-Pleistocene Transition. It also lines up with evolutionary events such as a recently discovered ancestral genetic bottleneck, which drastically reduced human diversity, and the timing of the chromosome 2 merger in hominins. Whether this is all a coincidence, or whether the intensifying glacial climate shifts contributed to the genetic transitions in early humans, remains an open question."
The Mid-Pleistocene Transition and Human Adaptation
The Mid-Pleistocene Transition, a significant climatic shift occurring around one million years ago, may have played a role in the temporary disappearance of topographic adaptations among hominins. This period was marked by changes in Earth's glacial cycles, which could have affected early human populations both genetically and behaviorally. Timmermann and his colleagues suggest that these shifts may correlate with other major evolutionary milestones, such as genetic bottlenecks and chromosomal changes.
The possibility that these glacial climate shifts influenced human genetic evolution remains a point of debate. However, the timing of these events provides a compelling narrative connecting environmental change with the evolutionary trajectory of early humans.
The Evolutionary Puzzle of Human Adaptation
The findings from the ICCP team add another piece to the complex puzzle of human evolution. Over millions of years, early human populations adapted to a wide variety of environmental challenges, with mountainous regions playing a significant role. The study indicates that, across continents and species, early humans were often "steeplanders," seeking out the diverse resources offered by rugged terrains.
Elke Zeller summarized the study's findings, stating,
"Our results clearly show that over time hominins adapted to steep terrain and that this trend was likely driven by the regionally increased biodiversity. Our analysis suggests that it was beneficial for early human groups to populate mountainous regions, despite the increased energy consumption needed to scale these environments."
Conclusion
The relationship between early human evolution and mountainous regions is a crucial element in understanding our origins. The diverse ecosystems found within these rugged landscapes not only offered early hominins a rich variety of food sources but also presented unique challenges that shaped their development. This study underscores the importance of environmental diversity in the evolutionary journey of humanity, revealing how early humans adapted and thrived as "steeplanders" in the face of natural challenges.
Zeller, E., Timmermann, A., Yun, K.-S., Raia, P., Stein, K., & Ruan, J. (2023). Human adaptation to diverse biomes over the past 3 million years. Science (New York, N.Y.), 380(6645), 604–608. https://doi.org/10.1126/science.abq1288