New research using climate models provides fascinating insights into how environmental conditions influenced the evolution and migration of early humans.
One study uses deep-sea sediment cores to trace the climatic factors that enabled or hindered hominin settlement in Europe, while another study explores the interbreeding opportunities between Neanderthals and Denisovans due to shifting climates. These findings not only enhance our understanding of human history but also underscore the impact of long-term climatic changes on human habitats and interactions.
Climate Modeling and Hominin Evolution
In two studies, researchers demonstrate how climate modeling approaches can fill gaps in our understanding of hominin evolution and migration.
Over the last several decades, research efforts into the lives of hominins – humans and their close ancestors – have shifted from identifying fossils and artifacts to understanding the environmental and climate settings in which they lived and how these factors could have influenced hominin evolution and migration. However, like the hominin fossil record, environmental and climate records that accurately capture environmental change and span the period over which hominins evolved and spread across the globe are uncommon and incomplete. Some of these limitations can be addressed through advances in analytical tools, particularly climate and ecosystem models, which can help fill these gaps and provide valuable new insights into hominin migration.
Insights from Deep-Sea Sediments
In one study, Vasiliki Margari and colleagues used a deep-sea sediment core, which provided a temperature record for Europe from 800,000 to 1.8 million years ago. Using these data, the authors created a climate envelope model and evaluated the geographic range of hominin species using climate variables such as temperature and precipitation.
Margari et al. discovered hominin presence around the Mediterranean before ~1.1 million years ago was characterized by long, stable interglacial conditions with short glacials that would have allowed for hominin establishment and long-term occupation.
However, extreme glacial conditions beginning around 1.1 million years ago would likely have made the region too cold for hominins to survive. Margari et al. argue that these extreme conditions likely led to the depopulation of Europe, which could have lasted for several glacial-interglacial cycles.
Climate Change and Interbreeding Dynamics
In another study, Jiaoyang Ruan and colleagues evaluate how climate shifts across central Eurasia during the Pleistocene could have facilitated interbreeding between Denisovans and Neanderthals. Genetic studies have revealed evidence of interbreeding between Neanderthals and Denisovans in Eurasia. However, much about these admixture events remains unknown.
Here, Ruan et al. developed a species distribution model combining extensive fossil, archaeological, and genetic data with transient coupled general circulation model simulations of global climate and habitat change for the past 400,000 years, which was used to determine the habitat preferences for both Neanderthals and Denisovans.
The researchers discovered that, although both species lived in a variety of environments, Neanderthals preferred temperate forests, whereas Denisovans lived in a much wider range of habitats. However, orbitally driven climate shifts in habitat caused the preferred habitats of Denisovans and Neandertals to overlap, providing opportunities for interbreeding between the two species.
Modern Techniques Unveiling Ancient Migrations
A similar Earth system model-based approach was used by Zeller et al. in a May 2023 study in Science, which combined climate and fossil datasets to evaluate habitat suitability and preference for several Pleistocene hominin species and how they responded to changing climatic conditions over the last 3 million years.
For more on this study, see New Study Reveals Ancient Cooling Wiped Out Early Humans.
References:
“Extreme glacial cooling likely led to hominin depopulation of Europe in the Early Pleistocene” by Vasiliki Margari, David A. Hodell, Simon A. Parfitt, Nick M. Ashton, Joan O. Grimalt, Hyuna Kim, Kyung-Sook Yun, Philip L. Gibbard, Chris B. Stringer, Axel Timmermann and Polychronis C. Tzedakis, 10 August 2023, Science.
DOI: 10.1126/science.adf4445
“Climate shifts orchestrated hominin interbreeding events across Eurasia” by Jiaoyang Ruan, Axel Timmermann, Pasquale Raia, Kyung-Sook Yun, Elke Zeller, Alessandro Mondanaro, Mirko Di Febbraro, Danielle Lemmon, Silvia Castiglione and Marina Melchionna, 10 August 2023, Science.
DOI: 10.1126/science.add4459
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