A leap in stone tool complexity in the fossil record suggests hominin knowledge underwent a sudden increase around 600,000 years ago, helping explain how modern humans and our ancestors became especially proficient at adapting to new environments.

It's a timing that could potentially even "predate the divergence of the Neanderthal and modern humans and be a shared derived feature of both lineages," explain University of Missouri anthropologist Jonathan Paige and Arizona State University anthropologist Charles Perreault, who report these findings in a new paper.

The researchers analyzed stone tool manufacturing techniques across 3.3 million years of human evolution. They ranked 62 tool-making sequences in order of their complexity for tools found across 57 sites.

The oldest artifact was from Africa, but ancient tools from Eurasia, Greenland, Sahul, Oceania, and the Americas were included in the analysis.

Paige and Perreault found that up until 1.8 million years ago the manufacture sequences of stone tools ranged between two and four procedural units in length. Over the next 1.2 million years an increase in tool complexity took place, reaching up to seven procedural units.

It wasn't until around 600,000 years ago, however, that our ancestors took this to a whole new level.

By this point tool complexity could require up to 18 procedural units. Such a large technological advancement relies on knowledge passed on from previous generations – a cumulative culture – Paige and Perreault suggest. In the generations that followed, point stone tool complexity continued to increase rapidly.

"Cumulative culture is the accumulation of modifications, innovations, and improvements over generations through social learning," Paige and Perreault define in their paper.

"Generations of improvements, modifications, and lucky errors can generate technologies and know-how well beyond what a single naive individual could invent independently within their lifetime. When a child inherits her parent's generation's culture, she inherits the outcome of thousands of years of lucky errors and experiments."

Cumulative culture benefits a population in a number of ways, increasing the chance of solving problems through generations of trial and error much like evolution does through random mutations and natural selection. It also allows individuals to use and advance technologies without needing to fully understand every aspect of their development, opening the way for an ever-increasing and adapting knowledge pool.

As this collective knowledge and associated behaviors grew, genes that affect learning may have also been selected for.

"Products of this gene-culture coevolution process may include an increase in relative brain size, a prolonged life history, and other keystone traits underlying human uniqueness," Paige and Perreault explain.

While the team's findings provide a solid proxy for the presence of cumulative culture near the beginning of the Middle Pleistocene, this type of cultural intelligence may have arisen even earlier in our evolutionary history, Paige and Perreault note, in ways that weren't so easily preserved.

"It is possible that early hominins relied on cumulative culture to develop complex social, foraging, and technological behaviors that are archaeologically invisible," they write.

Regardless of the exact technology or timing, reliance on cumulative culture may have provided a strong selective force that shaped many of humanity's unique features.

This research was published in PNAS.