Decoding the mysteries of Homo sapiens' survival: study reveals three million years of adaptation

Specifically, it explores how six Homo species adapted to environmental changes and more extreme habitats, and the subsequent impact on their survival and migration from Africa to Eurasia.

To delve into the profound implications of the study and its relevance to our comprehension of human survival, Interesting Engineering (IE) interviewed the study's lead author, Elke Zeller, from the Center for Climate Physics at the Institute for Basic Science (IBS) in South Korea. 

Homo sapiens as broad biome dwellers

Zeller elucidates that adaptation to different biomes (ecological regions) is essential in hominin evolution because it broadens the variety of food resources they could utilize. 

"Our results showed that Homo sapiens lived in more biomes than any other hominin species, and they preferred to live in places with multiple biomes (mosaic landscapes), so they would have had access to the widest variety of resources."

Additionally, Zeller explains that such adaptability likely provided Homo sapiens with a notable edge over other hominin species.

While her team did not directly investigate competition in their study, she acknowledged the intriguing nature of the question, expressing their intention to delve into it in future research.

The team achieved their results by integrating a transient Earth system-biome model simulation (BIOME4), spanning 3 million years, with archaeological and fossil data for six distinct Homo species. 

Their investigation revolved around determining the favored environmental conditions of these hominin species, tracking changes in biome preferences over time, as well as diversity throughout the Pleistocene, and examining how these choices influenced hominin adaptation.

"This output is from a combination of two different models. First, we used a climate model (CESM) to estimate the past climate," Zeller told IE. "Secondly, we fed that information (temperature, precipitation, and clouds) into a vegetation model (BIOME4), translating this data into biomes."

She clarified that biomes represent geographic areas characterized by comparable climates, flora, and fauna. Common examples include savanna, rainforest, and tundra.

"Climate models often get confused with statistical models, but they are very different. Climate models are comprehensive models that often use over one million lines of code," she said. "They solve the equations of motion and thermodynamics over the globe."

In other words, climate models work by solving equations that describe the motion and thermodynamics across the entire planet. This is similar to how weather forecasting predicts atmospheric conditions and how studying ocean circulation helps understand water movement in the oceans. 

Furthermore, the researchers used a vegetation model to incorporate biogeography and biogeochemistry processes to provide the most accurate estimation of the type and distribution of vegetation based on the prevailing climate conditions.

3000 fossil and archaeological clues

Zeller clarified that the team had access to an extensive database comprising more than 3000 fossil and archeological records. Each record in the database provided specific information, such as the location (latitude and longitude) and an estimated age range (minimum and maximum age).

"In the vegetation data, we extracted, for each finding, the vegetation data corresponding to the age estimate at the location of the finding," she said. 

"Using statistical analysis, we then assigned probabilities of finding these fossils in specific vegetation types (different biomes) and the spatial variability of the vegetation, which we called biome diversity in our paper."

"Hominins were able to adapt to different environmental conditions, allowing them to expand geographically," Zeller accentuated.

Specifically, their analysis showed that early African hominins, like H. habilis and H. ergaster, mainly lived in open grasslands. H. erectus, after leaving Africa, settled in a broader range of environments, including temperate forests. More recent species like H. heidelbergensis and H. neanderthalensis also adapted to colder habitats.

"In addition, we found clear evidence for the clustering of early human occupation sites in regions with increased biome and biodiversity." 

The team found H. sapiens were capable of occupying even the most extreme environments, such as deserts and tundra. This ability indicates the development of advanced cognitive skills, allowing them to exploit diverse habitats and food resources.

Overall, the study reveals a pattern where Homo species preferentially selected and adapted to areas with a greater variety of habitats over the past 3 million years.

Based on these discoveries, the team put forth an innovative hypothesis known as the diversity selection hypothesis. According to this hypothesis, early human species preferred landscape mosaics, providing them with a broader spectrum of food resources. 

As a result, this preference enhanced their ability to withstand environmental challenges and thrive in various conditions.

The intriguing quest to understand Homo adaptation

Zeller provided a clear and resolute response when asked about the motivation behind studying Homo adaptation to diverse environments: she was driven by the inherent fascination of unraveling our ancestral history. 

"How we got where we are, and the changes our genus has gone through over the past are fun and challenging questions to work on," she said. 

No doubt, understanding the journey that led us humans to our present state and exploring the transformations our genus has undergone throughout the ages presented an intellectually stimulating and enjoyable challenge for Zeller and her team.

"With our supercomputer Aleph, I had the unique opportunity to look at Earth's vegetation history over the past 3 million years and connect this with the archeological data. This synthesis of big data is something I really like to do," she said. 

Such a study sheds light on the enduring mystery of why Homo sapiens is the sole remaining Homo species. By examining the relationship between hominins and their ecological environment, the research uncovers the significance of adaptation over the course of 3 million years. 

We now know Homo sapiens demonstrated remarkable adaptability by inhabiting diverse biomes and mosaic landscapes, granting them access to various resources. Additionally, the role of this adaptability in potentially providing Homo sapiens with a competitive advantage offers valuable insights into our ancestral history. 

It's intriguing to learn how scientists harness the power of climate and vegetation models, fossil records, and supercomputers to comprehensively understand Homo adaptation and the remarkable journey that led us to our present state.

Further research aims to explore competition dynamics among early hominin species.