How Did Humans Take Over The Planet?

There are two forces that contributed to this success. Obviously, we owe a lot of our planetary dominance to our biological evolution, but this occurred along with our cultural evolution. And according to new research from Arizona State University, this latter force may have actually been the decisive factor for our global dominance.

Around 70,000 years ago, humans began to expand outside of Africa, with specific subsets moving into Eurasia around 60,000 years ago. This was a quick and wide-ranging dispersal, and by 50,000 years ago, we had navigated the deep ocean channels that separated Asia from Sahul – a prehistoric continent that connected Australia to Tasmania and New Guinea.

Through this large-scale movement, humans came to live in nearly all terrestrial habitats on the planet. By around 45,000 years ago, some humans were hunting mammoths in Arctic conditions, while others were thriving in the tropical rainforests of Sri Lanka. As the Pleistocene ended (around 11,700 years ago), we had spread to pretty much every major ecosystem on Earth.

In order to achieve this, humans had to accumulate certain adaptive evolutionary changes. For instance, there are populations of humans who have adapted to live at high altitudes who demonstrate unique physiological and metabolic adaptations. Others have developed resistance to specific diseases, while some have become more tolerant of colder weather or even protein-rich diets. But alongside these biological changes were cultural adaptations.

Cultural evolution is a population-wide, rapid, transformative process where human societies’ beliefs, behaviors, and knowledge change due to social learning rather than genetic inheritance. In practice, it is the process whereby information – such as technologies, language, and traditions – is accumulated and passed from one generation to the next. In terms of time, cultural evolution can occur far more quickly than genetic inheritance, allowing humans to accumulate beneficial innovations at a much faster pace.

There has been a growing body of empirical research into ways cultural evolution has benefited human behavior, but its role in human expansion across the planet is still unclear. That’s where this new study comes in.

According to the researcher’s findings, humans occupy about 132 million square kilometers (51 million square miles) of land on Earth. The typical wild mammal species, on the other hand, occupies about 166 square kilometers (64 square miles). The research argues that if humans were an average mammal that only relied on genetic evolution, then they would have needed tens of millions of years, along with thousands of separate species and vastly different body sizes, to achieve this geographic range.

“As humans moved into new environments, they didn’t have to wait for genetic mutations to adapt to Arctic cold, tropical forests, deserts or high altitudes,” study author Charles Perreault, a research scientist at the Institute of Human Origins and an associate professor at ASU's School of Human Evolution and Social Change, said in a statement.

“Instead, humans adapted through culturally transmitted technologies, ecological knowledge and cooperative social norms. Innovations in clothing, shelter, hunting strategies, food processing and social organization could spread rapidly through social learning.”

Perreault believes this evidence helps explain human uniqueness in a measurable evolutionary perspective.

“We often say that culture makes us different, but here we can estimate by how much. The results suggest that cultural evolution compressed what would normally require roughly 88 million years of biological diversification into about 300,000 years within a single species,” he explained.

“It reframes recent human history as a kind of adaptive radiation – but one powered by cultural diversification rather than speciation – and shows that adding a cultural inheritance system changes how quickly and extensively a lineage can expand.”

To achieve this conclusion, Perreault created geographic range maps for around 6,000 species of terrestrial mammals, grouping them into genera, families, and orders, before comparing the size and ecological diversity of those ranges with the global human range. After this, he explored how range sizes may relate to lineage age, number of species, and body-mass variation – three indicators of evolutionary change. These relationships allowed him to estimate how much biological diversification a mammalian clade would need to become as wide-ranging as us. 

Lastly, Perreault modeled how range size relates to cultural group territories to see whether cultural evolution allows humans to specialize at finer spatial scales. This would show that culture enables humans to be a globally generalist species while also being locally specialized as a cultural group.

“This study is part of a broader effort to build a quantitative science of human macroevolution,” Perreault added.

“By combining large comparative datasets with evolutionary theory, we can begin to measure the distinctive role of culture in shaping our species’ trajectory in a way that would have been almost impossible before.”

The study is published in the journal Proceedings of the National Academy of Sciences.