Climate change shaped human evolution, driving migration and cultural adaptation across ancient landscapes

By Dr. Chinta SidharthanReviewed by Susha Cheriyedath, M.Sc.Sep 15 2024

New insights into how climate shifts sparked the migration and survival of early humans, revealing the crucial role of environmental adaptation in our evolutionary history.

Review: Past climate change effects on human evolution. Image Credit: Daniel Eskridge / Shutterstock

In a recent review published in the journal Nature Reviews Earth & Environment, researchers discussed the role of climatic shifts and vegetation changes in driving the evolution within the subfamily Homininae, to which humans belong. They focused on the evolution of hominins during the Pleistocene in Eurasia and Africa, the two areas that have been extensively studied through anthropological and modeling studies.

Background

Human evolution has been significantly impacted by the climatic shifts that occurred between the beginning of the Pleistocene epoch and the Holocene. These climatic changes included periods of cooling and warming and shifts in dry and wet conditions, which influenced where early humans lived and the cultural and biological adaptations that contributed to their evolution.

Although early Homo species evolved from a common ancestor into several species with larger brains and improved cold tolerance, and spread all over the world, developed tools, and learned to control fire, only one species, Homo sapiens, remains. Climatic models and modern techniques can help understand how early humans responded to changing climates and the role climate played in the diet, migration, adaptation, and even extinction of species from the genus Homo.

Climatic modeling

The researchers discussed the three major approaches used in modeling human responses to climatic shifts to understand how early humans adapted to Pleistocene climatic changes. The approaches included species distribution models (SDMs), density-based models, and agent-based models.

In SDMs, species occurrences are correlated with environmental conditions to predict habitat suitability for a species. Using a combination of archeological and fossil data for paleoclimate simulations, SDMs can identify a species' realized niche and assess how factors such as resource availability and temperature can influence the species' dispersal.

Density-based models use demographic factors such as mobility, mortality, and reproduction to predict a species' population density and growth over time. These models can simulate population growth during resource availability and the decline in numbers when a species exceeds the carrying capacity. Integrating paleoclimate data into these models can provide insights into the migration and adaptation of early humans.

Agent-based models can simulate the behavior of individual agents, such as humans, and their interactions with each other and the environment to determine how small-scale behaviors can lead to large-scale population patterns.

Paleoclimatic changes

The ecosystem and climate underwent significant changes during the period in which early Homo species evolved into the current Homo sapiens, from 2.8 million years ago to 10,000 years ago. The Earth's climate underwent glacial cycles influenced by the planet's tilt, wobble, and orbit, which affected the distribution of solar radiation and led to variability in climate.

These glacial shifts caused changes in temperature and precipitation, resulting in notable shifts in tropical rainbands and monsoon systems, which impacted human evolution. The Pleistocene epoch is marked by cold glacial periods interspersed with warmer interglacial periods, which altered the ecosystems.

Subsequently, the biomes, which are regions with defined environmental conditions and vegetation, also underwent changes in response to the shifting climates. The climatic shifts during the Pleistocene resulted in substantial alterations in the dominant biome types. In Europe, the temperate forests were replaced by grasslands and tundra during the glacial periods.

Similarly, in Africa, rainforests were replaced by shrublands and grasslands during the mid-Pleistocene. Furthermore, the precessional cycles, which are determined by the wobble in the Earth's axis of rotation, also caused oscillations in the vegetation of North Africa, which is believed to have created green corridors that facilitated human migration between Africa and the neighboring regions.

Climatic changes and human evolution

The review also extensively discussed the role of climate in the evolution within the subfamily Homininae by exploring several key themes, such as the impact of climate on resource availability and habitat, which lead to Homo species either seeking out preferred environments, adapting, or facing extinction.

Climatic shifts also led to the expansion of the niche for Homo species, where Homo erectus and Homo sapiens migrated out of Africa into Europe and adapted to boreal and temperate forests. Additionally, hypotheses such as the Savanna hypothesis also propose that the climatic shifts that caused drying and cooling in Africa during the Pleistocene drove the evolution of bipedalism in Homo species. Similar hypotheses also emphasize the role of climatic shifts in the evolution of the brain.

Windows of favorable climate are also believed to have aided in the migration and distribution of Homo species out of Africa and into Eurasia, with Homo sapiens showing an unprecedented ability to disperse vast areas during the Holocene.

Furthermore, climatic shifts, along with competition, also played a role in extinctions, as in the case of Neanderthals, where shifting climates and technological advances gave Homo sapiens an advantage over the Neanderthals.

Cultural adaptations, such as the use of fire, tools, and clothing, not only helped Homo sapiens survive demanding environments but also expanded their ecological niches and allowed them to disperse to new regions.

Conclusions

To conclude, the review described the role of Pleistocene climatic changes in shaping human evolution, from driving habitat adaptations and migration to technological innovations. The environmental pressures due to these climatic shifts led hominins to adapt and expand their niche, resulting in the dispersal and survival of a resilient species — Homo sapiens.