Paleoclimate variability, mechanisms, and impacts on early humans​

K. Dulias, D.-K. Chinnaswamy, S. Wagner, A. Schwalb

One of the most compelling and pressing questions that researchers are exploring is how humans live, survive, and move in changing climates and environments. The past climate has played a significant role in shaping human evolution and history. For instance, during the Ice Age, humans underwent a transformation both physically and mentally to survive in harsh conditions. They had to migrate to more habitable lands as the climate changed. When the Last Ice Age ended, the warmer climate supported new ecosystems, which led to the cultivation of crops. By adapting to changing conditions, civilizations have been able to thrive and innovate, ultimately leading to the world we know today.

Climate modelling of the past
One particularly interesting topic to explore is the role of climate on early humans in northern Europe, who lived in harsh climates with abrupt shifts. Late Pleistocene global population distributions were influenced by orbital-scale climate shifts, while millennial-scale abrupt events had their impacts limited to local distributions (Timmermann & Friedrich 2016). Figure 1 shows the seasonal climatology of surface temperatures during the Last Glacial Maximum in contrast to pre-industrial conditions, providing a glimpse of how the basic climate state is changing and its potential to influence human environments in northern Europe. Further, when it comes to millennial timescales, Heinrich events (HE) (known to have significant impacts on Northern European climate) are also of potential interest. Müller et al. (2011), argue that the climate during Heinrich 5 Stadial forced the Neanderthals to leave their territories, providing a window of opportunity for the anatomically modern humans to spread into Europe before the Neanderthals reoccupied. This helped shift the balance in favor of modern humans. Furthermore, the landscape elevation due to ice sheets led to strong winds (katabatic winds) that affected nearby areas. So how these winds influenced climate might have significantly impacted human habitats, and it also has major importance for the climate during HE (Roberts et al., 2014).

To gain insight into these processes requires information on multiple climate parameters at varying scales, so we rely on paleoclimate model climate simulations. However, climate models have their own biases (Fig. 2), so to achieve robustness and narrow down uncertainties, a multi-model approach will be a wise choice. Furthermore, the lack of high spatial and temporal resolution in general circulation models (GCMs) poses a challenge in understanding fine-scale processes. This can be overcome using regional climate model simulations, while GCMs provide insights into the mean climatic state and large-scale dynamics.

Figure 1: Seasonal climatology of surface temperature of Last glacial maximum (LGM) and Pre industrial control runs (PI) by CNRM model. Units °C.
Figure 2: Seasonal climatology difference in surface temperatures during LGM run of CNRM and MIROC models. Units °C.

*The models used are part of CMIP6 PMIP datasets downloaded from Earth System Grid Federation.

Paleogenetics – Understanding the past using sedimentary ancient DNA
Paleogenetics is a relatively young research field which excelled in the last two decades, especially since the Neanderthal Genome Project (Green et al., 2006; Noonan et al., 2006). Since the Denisovan has been discovered, human migrations have been disentangled, ancestry patterns discovered and kinships analyzed. Simultaneously, ancient DNA has been utilized in environmental research to study paleoenvironments and past biodiversity of a diverse range of organisms (Capo et al., 2021). In this project we will combine the use of environmental ancient DNA, in our case sedimentary ancient DNA (sedaDNA) with ancient DNA (aDNA) of fossil remains to push method development, as well as add additional information to the paleoenvironmental reconstructions of other subprojects within the CCEHN project.

The analysis of human or humanoid DNA from sediments is still in its infancy and not yet widely applied. Since the sedaDNA content of humanoid origin is extremely low within the already very low abundance of sedaDNA in the environment, extraction and further analysis depend on specific protocols and large sequencing efforts. In this project we will analyze sediments from burials, e.g., the Mesolithic burial from Groß Fredenwalde, and from faunal remains in the Einhornhöhle in the Harz mountains. DNA extracts of both the surrounding sediment attached to fossil remains, as well as the fossil remains themselves will be sequenced and analyzed with the goal of eventually attaining a protocol for sedaDNA to analyze humanoid and faunal genomes hidden in the sediments of archaeological sites with no or just limited fossil preservation. First successful attempts of this approach have been done by Slon et al. (2016, 2017).

Established protocols for the reconstruction of past environments will be used to study paleolakes and other sites already under investigation within the CCEHN project. This data will complement the existing pollen records.

In conclusion, understanding the role of climate on human evolution and history is crucial for predicting and mitigating the impacts of future climate change. The use of paleoclimate models, climate simulations, proxies, and archaeological evidence will continue to play a key role in advancing our understanding of the complex interactions between humans and their changing environments.

Figure 3: Dr. Katharina Dulias extracting DNA in the ancient DNA laboratory.
Figure 4: Mesolithic burial in Groß Fredenwalde, Brandenburg

Capo, Eric, et al. „Lake sedimentary DNA research on past terrestrial and aquatic biodiversity: Overview and recommendations.“ Quaternary 4.1 (2021): 6.
Green, Richard E., et al. „Analysis of one million base pairs of Neanderthal DNA.“ Nature 444.7117 (2006): 330-336.
Müller, Ulrich C., et al. „The role of climate in the spread of modern humans into Europe.“ Quaternary Science Reviews 30.3-4 (2011): 273-279.
Noonan, James P., et al. „Sequencing and analysis of Neanderthal genomic DNA.“ science 314.5802 (2006): 1113-1118.
Roberts, William HG, Paul J. Valdes, and Antony J. Payne. „Topography’s crucial role in Heinrich Events.“ Proceedings of the National Academy of Sciences 111.47 (2014): 16688-16693.
Slon, Viviane, et al. „Mammalian mitochondrial capture, a tool for rapid screening of DNA preservation in faunal and undiagnostic remains, and its application to Middle Pleistocene specimens from Qesem Cave (Israel).“ Quaternary International 398 (2016): 210-218.
Slon, Viviane, et al. „Neandertal and Denisovan DNA from Pleistocene sediments.“ Science 356.6338 (2017): 605-608.
Timmermann, Axel, and Tobias Friedrich. „Late Pleistocene climate drivers of early human migration.“ Nature 538.7623 (2016): 92-95.

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