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Oct 13th 2021

In Human Evolution, Neighbors Were Allies Rather Than Enemies

Throughout human evolution and human history, relationships with other humans have come with risk and opportunity. This is true of relationships with individuals and with groups. Many anthropologists believe that the need to navigate complex social interactions was a major force that drove the evolution of large human brains.

Sharp rocks for stone tools

The fossil record suggests that human ancestors were participating in complex social interactions 300,000 years ago, during the Middle Stone Age. As a paper published in Science explains, human ancestors living in Kenya likely had a trade network to distribute materials for stone tools. While many archaeological sites from this time period included tools made from local rock, one site had stone tools made from glassy volcanic obsidian.

Careful analysis revealed that the obsidian came from multiple sources that were 25 to 95 kilometers away in multiple directions. When traveling by foot over the rocky terrain, the actual path would have been even longer. In present-day Africa, the remaining hunter-gatherer families generally only travel within a 20-km radius in a given year but maintain trade relationships with groups up to 100 km away.

The Kenyan site contained a large number of finished obsidian tools (mostly sharp points for projectile weapons), large pieces of unfinished obsidian and evidence that the site was used repeatedly over many years. Thus, the simplest explanation is that neighboring groups developed stable trade networks to move significant quantities of this valuable stone.

Human Evolution and Climate Change

Many major milestones in human evolution have taken place within the context of climate change. According to the Smithsonian National Museum of Natural History, the earliest fossils attributed to Homo sapiens are from roughly 320,000 years ago during a period of dramatic climate change. As the Science paper describes, the fossil layers at the obsidian tool site from 300,000 years ago show that the once-stable lake environment had become unpredictable, with the lake drying up and the climate alternating between wet and dry. Present-day hunter-gatherer societies show that strong social networks and the willingness to use a wide range of strategies for subsistence are crucial for survival in such unpredictable environments, according to a paper published in Nature.

When conditions improve, the most adaptable groups are more likely to flourish in the new environment, often increasing their range. The first major expansion of Homo sapiens occurred 130,000 to 100,000 years ago, after a major ice age, according to work published in the Philosophical Transactions of the Royal Society B. Humans spread across Africa and into Europe and Asia. There was a clear increase in population size, although some human populations were soon replaced by Neanderthal neighbors.

After a mega-drought, there was another major migration out of Africa into Europe and Asia 70,000 to 50,000 years ago. These new neighbors displaced many of the groups from the first human migration. They even interbred with Neanderthals and possibly another hominid group called Denisovans.

Advantages of Diversity

While interbreeding with Neanderthals may seem like an extreme way of practicing diversity and inclusion, Homo sapiens did benefit. Neanderthals had been living in Europe and Asia since 400,000 years ago, and they were well adapted to the cooler climate. The changing climate and competition with humans finally drove Neanderthals to extinction 40,000 years ago, but they left their mark. Neanderthal DNA makes up 1.38% of the genome in modern East Asians, 1.15% in modern Europeans and 0.08% in modern African Luhya, as Nature reports.

After the last ice age, there was another major expansion during the Holocene Epoch. Hunter-gatherer-fishers expanded into all major regions of the world, including North and South America. Populations also increased in Europe and Asia, which led to the development of farming in western Asia. With strong social networks and unprecedented control over their source of food, farmers expanded their range through Europe and elsewhere. Local populations either had to assimilate — with many becoming farmers — or be replaced. Many populations chose to embrace diversity and inclusion, as evidenced by the rich diversity within the gene pool of modern peoples.

As humans currently face another major episode of climate change, we may do well to remember how early humans survived and thrived. They built strong social networks that allowed for the exchange of materials and ideas and were willing to try different approaches to achieve success. These same principles may prove critical in finding new ways to survive, thrive and innovate amidst today’s ecological challenges.

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