#492 Why did early humans leave Africa?

Why did early humans leave Africa? They were probably forced out by climate change, but they could have left because of their rising intelligence. Let’s look at the evidence for why paleontologists believe humans developed in Africa and then look at why they left.

Humans probably separated from the common ancestor we share with other great apes about 6 to 8 million years ago and started to walk on two legs about 4 million years ago. Early humans started to use tools about 2.6 million years ago and they were making handaxes by 1.76 million years ago. There have been about 20 different species of human over the last 4 million years and they all died out at one point or another, except for homo sapiens. Homo sapiens first appeared about 300,000 years ago. They differed from the other species of hominins because they had larger and more complex brains. Whatever mutation caused this gave them an advantage over the other groups of early man. They were able to adapt to changing situations more easily and they were able to communicate. They were able to make specialized tools. Other groups of early humans also made tools, but homo sapiens were able to use tools to make more specialized tools. They lived in shelters and were able to control fire. These advantages meant that they survived after all of the other groups of early human went extinct. In fact, homo sapiens could be the reason why some of the other groups went extinct.

So, how do paleontologists know that homo sapiens began life in Africa? There are three main reasons. The first one is mitochondrial DNA. We are made up of DNA that we receive from our mothers and our fathers. However, mitochondrial DNA we only receive from our mothers and it doesn’t change from generation to generation. The mitochondrial DNA in your cells is the same as your mother’s, and her mother’s, all the way back for thousands of years. When researchers looked at mitochondrial DNA they found that the amount of genetic diversity decreases the further away from Africa you go. They traced everything backwards and found the most recent common ancestor of all currently alive human beings was based in eastern central Africa.

The second reason is the size and shape of skulls. Similar to the mitochondrial DNA, the further away from Africa you go, the fewer differences there are. Central eastern Africa has the greatest diversity of skull sizes and shapes. And the third reason is simple archaeology. Human fossils and tools from two to three hundred thousand years ago have been found in these areas and not in any others. There is the chance that fossils are in other places but they have yet to be found, but it is more likely that humans started in Africa and then moved all over the world.

So, why did they leave Africa? Before we look at that, it’s worth noting that they didn’t just suddenly leave, we don’t really know exactly when they left, and they weren’t the first humans to leave Africa. It is theorized that they left between 80,000 and 60,000 years ago. Homo erectus, who are possibly an ancestor of homo sapiens, found their way into China, Indonesia, and Europe at least 2 million years before that. The homo erectus that stayed in Africa probably gave rise to homo sapiens. There is evidence that homo sapiens left Africa before the great migration, as well. Skeletons found in Israel have been dated from 100,000 years ago. Although, it doesn’t seem that these people went any further because no evidence has been found.

People could have left Africa because of climate change. About 70,000 years ago, the climate in the South east of Africa changed. The land was green and verdant, but the change made it much drier and colder. Deserts formed and the rains stopped. Homo sapiens were hunter-gatherers and if there were no rains, the animals would die. They had to move where the animals were, which meant migrating. Once they started to migrate, they could have just carried on.

Another reason they left could be a new way of thinking. About 80,000 years ago was a period of time known as the “great leap forward”. There is a sudden jump in the level of tool making. There is also the development of art, burial rites, and self-ornamentation. A lot of seashells have been found from this period, showing that homo sapiens were eating shellfish. Shellfish have a lot of fatty acids that our brains need and this could have caused a jump in intelligence. Being smarter might have made people want to head out and explore.

A third reason is probably just because we were looking for space. The population in one area might have increased enough that some people wanted to move out and find another area. This could have continued until new generations were far removed from the original generations.

So, homo sapiens probably left Africa about 60,000 years ago, but we might never know the reason why. And this is what I learned today.

Sources

https://www.history.com/news/humans-evolution-neanderthals-denisovans

https://humanorigins.si.edu/evidence/human-fossils/species/homo-sapiens

https://www.yourgenome.org/stories/evolution-of-modern-humans/

https://humanorigins.si.edu/education/introduction-human-evolution