Will climate change affect human evolution?
Since the 1920s, it has been suspected that climate change may have played a key role in human evolution. At that time, some scientists suggested that the drier environment may have caused early humans to begin to walk on two feet to adapt to life on the savannah. However, due to the limited number of historically representative paleoclimate data, this correlation has been difficult to prove.
Recently, a new study published in the journal Nature used an unprecedented model of circulation to simulate Earth's climate over the past 2 million years. Specifically, the new study explores how long-term climate fluctuations brought about by Earth's astronomical movements can create the environmental conditions that have stirred up human evolution.
When our Earth is pushed and pulled by other planets, its tilt and orbital shape will change, and the Earth's climate will change. For example, the Earth's tilt oscillates in a 41,000-year cycle, affecting the intensity of the seasons and rainfall in the tropics; in a period of more than 100,000 years, the Earth will change from a more circular orbit to a more elliptical orbit, with a more circular orbit bringing more sunlight and longer summers, while an elliptical orbit will reduce sunlight, which may lead to a period of glacier formation.
The simulations suggest that temperature and other planetary conditions influenced early human migration and may have contributed to the emergence of modern humans about 300,000 years ago. This result provides clear evidence for the claim that climate change has participated in shaping human evolution.
Ancient humans who appeared in simulated conditions
The researchers used a supercomputer to run a simulation containing these astronomical changes, reconstructing how temperature and rainfall might have affected humanity's available resources over the past few million years. They combined the simulations with thousands of fossil records and other archaeological evidence to deduce Homo sapiens, Homo neanderthalensis, Homo heidelbergensis, Homo erectus, and Homo ergaster and Homo habilis) all the places and times when these 6 human species appear in the model.
Although these different paleo-human species prefer different climatic environments, their habitats all respond to climate change caused by astronomical changes such as the oscillation, tilt and eccentricity of the Earth's axis. To examine the link between climate change and human habitat, the researchers shuffled fossil age like a shuffle, and if past climate change didn't affect where and when ancient humans lived, the same habitat should have been obtained.
The simulations produced vast amounts of data, and by analyzing them, the researchers found significant differences in habitat patterns between the three most recent paleoanthropologist groups of Homo sapiens, Neanderthals, and Heidelbergians, when using disrupted fossil ages and real fossil ages. This suggests that for at least the past 500,000 years, the true order of climate change has played an important role in determining where different groups of ancient humans lived and where their remains were found.
The researchers then set out to address the next question of whether the habitats of different human species overlap in space and time. They studied data from five major paleoanthroptic groups and found that early African paleominants between about 2 million and 1 million years ago preferred stable climatic conditions, which limited them to relatively narrow habitable areas. After a major climate shift some 800,000 years ago, the Heidelbergers adapted to a wider range of food resources, thus making them "global wanderers" and reaching remote areas of Europe and East Asia.
The preferred habitats for Homo sapiens (purple shaded on the left), Heidelberger (red shaded in the middle), and Neanderthals (blue shaded on the right) are shown. (Photo: Institute for Basic Science)
In the past, some scientists have suggested that the Heidelbergians may have produced many other species around the world, including Neanderthals in Eurasia and Homo sapiens somewhere in Africa. The new model suggests that a global distribution of Heidelbergians is possible, as more elliptical orbits create more humid climatic conditions that allow Heidelbergians to migrate more widely. From the simulations, Heidelbergians began to expand their habitat about 700,000 years ago, Neanderthals and Denisovans may have evolved from the Eurasian branch of Heidelbergers about 500,000 to 400,000 years ago, and Homo sapiens can be traced back to the late Heidelberg people of southern Africa about 300,000 years ago. This is very similar to recent estimates from genetic data or analysis of differences in human fossil morphology.
New approaches, new insights
These results were achieved through the use of the supercomputer Aleph. Aleph ran continuously for 6 months, completing the longest comprehensive climate simulation to date. The results of these simulations may provide new insights into where and how the human species emerged.
Paleoanthropology still has many controversial questions, and while new results are unlikely to end these debates, the study makes it clear that well-validated climate models have significant value in addressing fundamental questions about human origins. The researchers believe that the paleoanthropological community should make fuller use of the simulation potential of this continuous paleoclimate model.
The new study provides evidence that climate played an important role in human evolution, showing that we are who we are because we have successfully adapted to the slow changes in past climate over thousands of years. Of course, we need more evidence to prove that astronomical cycles affect the trajectory of human ancestors. Next, the researchers plan to run larger models that integrate genetic data.
#创作团队:
Author: Light rain
Typography: Wenwen
#参考来源:
https://phys.org/news/2022-04-early-human-habitats-linked-climate.html
https://www.sciencenews.org/article/climate-change-human-evolution-habitat-migration
#图片来源:
Cover image: Medi2Go/Pixabay
首图：Institute for Basic Science