Human evolution may have been influenced by astronomical factors about two million years ago, as a study published in the journal Nature revealed that major climatic changes associated with changes in the Earth’s orbit were what led to the migrations of the first humans.
Various species of Homo, such as Homo erectus, Neanderthals, and Homo sapiens (they are the only ones that survived), moved over hundreds of thousands of years through Africa and Eurasia, sometimes replacing one another, or at other times meeting, intersecting, and mixing in some cases. However, paleontologists find it difficult to reconstruct the spatio-temporal map of these ancient settlements, due to the lack of human fossils.
Or the solution to this problem lies in “digging” into the climatic past. There is no doubt that climate has influenced the movements of human groups through the changes it has brought about in terrestrial ecosystems. But in this field too, there is very little and sparse amount of geological data that provides an idea of environmental changes (polar cover, sediments of lakes, oceans, caves, etc.).
A study published in Nature may help complete the picture by showing how climate change, over a very long period of two million years, affects the distribution and spread of human species throughout the world.
Everything depends on the Earth’s orbit around the sun, according to climate scientist Axel Timmermann of Busan University in South Korea, the lead author of the study published Wednesday. The elliptical shape of this motion changes every 100,000 to 400,000 years, while the Earth’s axis relative to its orbital plane undergoes oscillations approximately every 20,000 years.
This long-range celestial mechanical mechanism affects the level of solar radiation that the planet receives, causing ice ages such as the Ice Age (2.6 million to ten thousand years ago) and alternating dryness and moisture, similar to the “green desert”.
Professor Timmerman likened this dynamic to the one that drives the pendulum, as it “ultimately determines where food is found, and therefore is linked to the continuity of the species, its adaptation to its environment and its migration,” he explained in the study.
His team relied on more than 3,000 fossil and archaeological data on which climate models were applied, and then a supercomputer simulated how the climate interacted with the astronomical clock.
The researchers then created a model that calculates the probability that a particular species inhabited somewhere on the planet, over 1,000-year epochs stretching between 2 million years ago and 30,000 years ago.
The model shows that the extended phase of the Lower Ice Age, a dry and cold period, 2.6 million years ago, came after the Pliocene period, which was wetter and warmer, witnessed the settlement of African groups such as Homo habilis and Homo employed in environments with “low climate variability, consistent with with low variance in Earth’s orbit.”
This behavior changed with the end of the Ice Age, as vegetation changed, and ‘corridors’ opened towards North Africa, the Arabian Peninsula, and Eurasia, allowing Homo erectus and Homo sapiens to become “global wanderers” capable of adapting to a wide range of climatic conditions. It is this flexibility that could explain the survival of the human species, according to the study.
The climate model also points to the pivotal role of Heidelbergensis, a human group discovered in Germany at the beginning of the 20th century that is believed to have lived between 800,000 years ago and 160,000 years ago. Most likely, the climatic disturbances that occurred in the southern part of Africa 300,000-400,000 years ago may have influenced the evolution of its individuals, who may have separated into a lineage in Eurasia with Neanderthals, and another in Africa from which the oldest members of the Homo sapiens lineage descend.
This hypothesis is expected to be the subject of a debate among deeply divided paleontologists over how to reconstruct the human evolutionary tree.
An anthropologist at the National Museum of Natural History, Antoine Balzou, said that the study, which he was not involved in preparing, collects an exceptional amount of environmental data over a long period of time, and he expected that “the model that was prepared will have applications that allow understanding human movements.”