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It has long been believed that climate shifts during the last 2 million years had a pivotal role in the evolution of our genus Homo1–3. However, given the limited number of representative palaeo-climate datasets from regions of anthropological interest, it has remained challenging to quantify this linkage. Here, we use an unprecedented transient Pleistocene coupled general circulation model simulation in combination with an extensive compilation of fossil and archaeological records to study the spatiotemporal habitat suitability for five hominin species over the past 2 million years. We show that astronomically forced changes in temperature, rainfall and terrestrial net primary production had a major impact on the observed distributions of these species. During the Early Pleistocene, hominins settled primarily in environments with weak orbital-scale climate variability. This behaviour changed substantially after the mid-Pleistocene transition, when archaic humans became global wanderers who adapted to a wide range of spatial climatic gradients. Analysis of the simulated hominin habitat overlap from approximately 300–400 thousand years ago further suggests that antiphased climate disruptions in southern Africa and Eurasia contributed to the evolutionary transformation of Homo heidelbergensis populations into Homo sapiens and Neanderthals, respectively. Our robust numerical simulations of climate-induced habitat changes provide a framework to test hypotheses on our human origin.

To investigate the role of vegetation and ecosystem diversity on hominin adaptation and migration, we identify past human habitat preferences over time using a transient 3-million-year earth system-biome model simulation and an extensive hominin fossil and archaeological database. Our analysis shows that early African hominins predominantly lived in open environments such as grassland and dry shrubland. Migrating into Eurasia, hominins adapted to a broader range of biomes over time. By linking the location and age of hominin sites with corresponding simulated regional biomes, we also find that our ancestors actively selected for spatially diverse environments. The quantitative results lead to a new diversity hypothesis: Homo species, in particular Homo sapiens, were specially equipped to adapt to landscape mosaics. Early humans and their hominin relatives had to adapt to new environments to spread out of Africa. Zeller et al. explored the movements of hominins across and preferences for different biomes by comparing six Homo species distributions from the fossil record against simulated climate and vegetation over the past 3 million years. They found that some later species inhabited a broader range of biomes as they spread to colder and more forested areas, especially H. sapiens, which settled in more extreme habitats (deserts and tundra). In addition to adapting to changing environmental conditions over time, models suggest that Homo species may have preferentially selected areas with more diverse habitats. ?Bianca Lopez Earth system modeling shows how Pleistocene hominins spread across and selected different habitats.

There are many interdisciplinary theories as to how climate variability impacted hominin migration, and subsequently human evolution. One such hypothesis concerns so-called “green corridors,” in which climate and biome variability periodically opened vegetated corridors between habitable areas. The periodic opening of these corridors may have acted as a pump through uninhabitable barrier regions, allowing for more wide-spread dispersal. We present results from a climate-forced agent-based model that furthers the green corridor hypothesis to include the effect of stochastic resonance in penetrating barrier regions. In other words, while it intuitively makes sense that hominins would explore and disperse as green corridors opened up, the potential for green corridors to act as a dispersal pump likely depended on having the right amount of stochasticity (randomness) in hominin movement to resonate with orbitally-paced climate signals, effectively penetrating these corridors and dispersing into other regions. We integrate data from a 2-million-year CESM model, from the BIOME4 vegetation model, and from archaeological archives to create a map of habitat suitability based on a species-specific climate envelope. This habitat suitability forces the agent-based hominin migration model, in which agents seek more habitable areas and the added randomness in that agent movement is varied. While our conclusions are largely independent of species, we show results from a Homo erectus migration simulation. In my presentation I will discuss how stochastic hominin movement, the opening up of green corridors, and climate variability affected hominin dispersal throughout the Plio-Pleistocene.

Climate influenced the evolution of hominins, though the mechanisms and scales are still not well understood. We know that long-term climatic variations, such as wet-dry climate cycles and sea-level change, can change landscapes dramatically. Changes in landscapes can drive early hominins to find different locations to settle, but what kind of environments did they prefer and what role did changing climates play in all this? To research this question, we modeled the climate of the past 3 million years using CESM, made a best estimate of the global biome landscape, and compared the results to an extensive archeological database of hominin findings.This analysis shows us that early hominins living in Africa predominantly lived in open habitats. When hominins expanded northwards, they adapted to more forested landscapes. While they were able to adapt, most hominin locations were found in areas with less variability and higher local biome diversity, suggesting that hominins prefer stable environmental conditions with a variety of resources nearby. This preference for stability and a landscape that offers diverse biomes is seen for all hominins regardless of species.

Genomic data document multiple episodes of interbreeding among Neanderthals, Denisovans and Homo sapiens. When, where and how often the interbreeding between these hominin populations took place remains unclear. Here, we study the Neanderthal-Denisovan admixture during the past 400 thousand years using a novel habitat model that integrates extensive fossil, archeological, and genetic data with unprecedented transient Coupled General Circulation Model simulations of global climate and vegetation. Our Pleistocene hindcast of habitat suitability reveals pronounced climate-driven zonal shifts in the main overlap region of Denisovans and Neanderthals in central Eurasia. These shifts, which influenced timing and intensity of potential interbreeding events, can be attributed to the response of climate and vegetation to past variations in atmospheric CO2 and northern hemisphere ice-sheet volume. Therefore glacial/interglacial climate swings likely played an important role in archaic human gene flow and genetic diversification.

It has previously been suggested that climate shifts during the last 2 million years played an important role in the evolution of our genus Homo. However, quantifying this linkage has remained challenging. Here we use an unprecedented transient Pleistocene Coupled General Circulation model simulation in combination with an extensive compilation of fossil and archaeological records, to study the spatio-temporal habitat suitability of five hominin species over the past 2 million years. We show that astronomically-forced changes in temperature, rainfall and terrestrial net primary production had a major impact on their observed distributions. During the early Pleistocene hominins primarily settled in environments with weak orbital-scale climate variability. This behaviour changed drastically after the mid-Pleistocene-transition when archaic humans became global wanderers who adapted to a wide range of spatial climatic gradients, which increased the likelihood for habitat overlap and cladogenic transitions. Our robust numerical simulations of climate-induced habitat changes provide a novel framework to test hypotheses on our human origin.