Homo sapiens appeared in the south of the continent about 300,000 years ago, and settlement helped him because of changes in climate, say the authors of a new paper.
What happened?
Climate change over the past 2 million years is thought to have played a major role in the evolution of our species. The authors of a new paper modeled Earth’s climate changes and linked habitable areas to known archaeological findings and fossils. The researchers suggest that our species evolved in a region in southern Africa 300,000 years ago.
But there is another theory that disputes this idea. To deal with this contradiction, a team of researchers from South Korea and Europe modeled the Earth’s climatic history over 2 million years and compared it to locations where ancient human bones and tools were found.
The study’s lead author, Axel Timmermann of the Institute of Basic Sciences at Busan University, said this is the first study linking archaeological evidence to climate change. It will help piece together the history of how humans moved and evolved.
Ian Moffat, a geoarchaeologist at Flinders University, said the study looked at the main places where early human evolution took place – Africa, Europe and parts of Asia.
What do we know about early human evolution?
The genealogical tree of the human species is a tangled scheme with a huge number of branches, among which there are many forks, branches and dead ends – and some branches connect several times over the millennia as different species cross and migrate.
Scientists believe that our ancestors began to actively move and populate new territories because of climate change. For example, when a familiar region ceased to be comfortable and suitable for living, as compared to a neighboring region. But it is not easy to determine what the climate used to be in a particular area inhabited by people.
Researchers have several methods: dating sediments and analyzing particles, such as pollen that remained in the soil and rocks. In this way, it is possible to find out what kind of plants grew in this place, and from this it is already possible to draw conclusions about the climate. But caves will give less information about the climate, as they are usually sheltered and dry and are less likely to be affected by the external environment.
How did the authors model the weather?
In the new study, to study climate change, the authors used a computer model – the same type of model used by an intergovernmental panel of experts in their report on climate change. Previously, it was used to predict future climate change, but now to learn about events that occurred 2 million years ago.
The climate cycles that the team modeled were different from today’s climate change. The situation today is related to an increase in carbon emissions into the atmosphere.
Why was the climate changing in the past?
Climate changes 2 million years ago were due to astronomical climate cycles. They are also called Milankovic cycles: they are named after the Serbian researcher who is believed to have first announced their existence in the 1920s.
There are several types of Milankovitch cycles – one of them is related to the distance from the Earth to the Sun. Our planet revolves around the Sun, but it does not move in a perfect circle. There is a gravitational pull from Jupiter and Saturn, which causes the trajectory to become oval-shaped. This means that the Earth is farther away from the Sun for some time and receives less heat.
Another Milankovitch cycle occurs because the gravitational pull of the Moon and Sun affects the shape of the planet and flattens it slightly closer to the poles. When the Earth rotates around its tilted axis, one hemisphere receives more radiation from the Sun and the other receives less. The authors of the new work note that changes in the Earth’s tilt also affect the climate, but to a lesser extent. Milankovitch cycles cause the planet to warm and cool for tens of thousands to hundreds of thousands of years, but they cannot explain the Earth’s warming today.
What have we learned from climate modeling?
The team modeled Earth’s climate for most of the geologic epoch called the Pleistocene. At the beginning of the Pleistocene, about 2 million years ago, a cool cycle began. It was around this time that the first waves of early human migration from Africa began. Probably one of the first migrating species was an ancient relative of modern humans, Homo erectus.
The researchers found that their climate predictions agreed fairly well with real evidence of migration – for example, with ice drilled deep into the polar ice sheets. Based on their simulations, the team created maps that showed which areas were suitable for human habitation. The data were based on precipitation and food availability.
They then overlaid those maps with more than 3,200 archaeological finds from six human species, including our species, Neanderthals and H. heidelbergensis, which is thought to have appeared in Africa about 800,000 years ago.
So the researchers saw how the environment in which each human species preferred to live differed. They found, for example, that ancient humans lived in regions with a stable climate, while people who appeared later, such as H. heidelbergensis, were nomadic and settled in more harsh and arid conditions.
Maps also showed where one form of early man disappeared and another appeared. This shows how one species evolved into another. For example, this happened with H. heidelbergensis in two places at the same time. About half a million years ago, H. heidelbergensis spread from southern Africa all over Europe and possibly also into Asia. About 400,000 years ago, the number of H. heidelbergensis decreased and Neanderthals appeared. Then 300,000 years ago, H. sapiens. began to push H. heidelbergensis out of southern Africa.
What was the main influence of climate on ancient human life?
According to the authors, around the time H. sapiens appeared, Africa was becoming very dry. The environment became less habitable. The team stated that H. sapiens dispersed from just one region in Africa.
But there is another theory – H. sapiens did not evolve from a single region, but arose from multiple divided populations across the African continent that interbred with each other.
Climatic models from the new study showed that suitable human habitats were in both eastern and southern Africa. But archaeological and fossil evidence confirms that our species originated in the southern region.
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