Climate Change Controlled Where Early Humans Lived

Asian Scientist (May 11, 2022) – Astronomically driven climate change influenced where various archaic humans—a broad group including Homo sapiens, Denisovans, and Homo neanderthalensis who roamed the earth about 2.3 million years ago—lived and when they moved to new locations. The link was clearly established in a recent Nature study by an international research team, led by scientists in South Korea.

Astronomical climate change refers to a phenomena where the Earth’s climate is affected by astronomical factors. For example, gravitational perturbations from other planets, most notably, Jupiter and Saturn, affects the Earth’s axis of rotation. That is one of the reasons why the Earth experienced a succession of alternating glacial and interglacial epochs in the past.

The researchers logged in extensive archaeological data of human habitation into a computer simulated model of the earth’s climate history covering the past two million years. They wanted to determine under which environmental conditions archaic humans likely lived. While the impact of astronomical climate change on human evolution and migration has long been suspected, this study establishes that, and is the first one to do so.

“Even though different groups of archaic humans preferred different climatic environments, their habitats all responded to climate shifts caused by astronomical changes in earth’s axis wobble, tilt, and orbital eccentricity with timescales ranging from 21 to 400 thousand years,” said Axel Timmermann, lead author of the study and director of the IBS Centre for Climate Physics (ICCP) at Pusan National University, South Korea. “Changes in earth’s orbit and axes influence the seasonality of sunshine at any given latitude. These parameters oscillate with periods of 20,000, 40,000, 100,000 and 400,000 years. For example, 10,000 years ago the northern hemisphere summer was closer to the Sun than now.”

In an earlier paper linking climate change and human migration, Timmermann had found that orbital-scale global climate swings played a crucial role in the migration and population distribution of early humans.

In the recent study, the scientists first used their computer simulation of paleo-climatic conditions to see what the climate was like at various times and places where early humans lived, as per archaeological records. Through that investigation, they were able to find the preferred environmental conditions of different groups of hominins. After that, the team looked for all the places and times those conditions occurred in their simulation. This helped them create maps of potential habitats of various hominin species over different times in the Earth’s history.

To test the robustness of the link between climate and human habitats, the scientists repeated their analysis by randomising archaeological records and the age of fossils. The idea behind randomisation was that if the climatic variables did not impact the choice of location where humans lived, then both methods would result in the same results. This was not the case though. The researchers found significant differences in the habitation patterns for the three most recent hominin groups (Homo sapiens, Homo neanderthalensis, and Homo heidelbergensis) when using the randomised and the realistic archaeological records.

The scientists were also able to demonstrate that astronomically induced climate shifts were a key factor in driving not only hominin species distributions but also their diversification or intermixing with each other. “This result implies that at least during the past 500,000 years, the real sequence of past climate change, including glacial cycles, played a central role in determining where different hominin groups lived and where their remains have been found,” said Timmerman. Following this study, the researchers hope to study the impact of past climate change on human genetic diversity.

A key advantage for the researchers who were doing this study was access to one of South Korea’s fastest supercomputers, called Aleph. Located at the Institute of Basic Science in Daejeon, Aleph ran non-stop for over six months to complete the longest comprehensive climate model simulation to date. Over 500 terabytes of data was generated during the study. “This study is based on what is called ‘transient simulations’ – so climate reconstruction is not done in bits and pieces for those periods but as a long continuous simulation,” Raghu Murtugudde, earth systems scientist at the University of Maryland, told Asian Scientist. “It is expensive computationally but the best way to ensure consistency across the study period.” Murtugudde, who is Indian, was not part of the study.

He added, “When combining the study’s key findings with the climate impact on civilisations during the Holocene, it is clear that humans are quite vulnerable to climate change even when perturbations are relatively small. But now we are making massive perturbations. The biggest follow up would be to see how evolution of bipedalism and cranial growth itself was affected by climate transitions and where we are headed now with this warming.”

Source: Pusan National University, South Korea; Photo: Shutterstock

The article can be found at: Timmermann et al. (2022) Climate effects on archaic human habitats and species successions