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Changing environment influenced human evolution

An aerial view of scrubby, sand coloured landscape divided by dry channelsImage copyright Human Origins Program, Smithsonian
Image caption Olorgesailie Basin: the dig site spans an area of 65 square kilometres

Humans may have developed advanced social behaviours and trade 100,000 years earlier than previously thought.

This is according to a series of papers published today in Science.

The results come from an archaeological site in Kenya's rift valley. "Over one million years of time" is represented at the site, according to Rick Potts from the Smithsonian Institution, who was involved in the studies.

There are also signs of developments in toolmaking technologies.

Environmental change may have been a key influence in this evolution of early Homo sapiens in the region of the Olorgesailie dig site.

The world turned upside down

Early humans were in the area for about 700,000 years, making large hand axes from nearby stone, explained Dr Potts.

"[Technologically], things changed very slowly, if at all, over hundreds of thousands of years," he said.

Then, roughly 500,000 years ago, something did change.

A period of tectonic upheaval and erratic climate conditions swept across the region, and there is a 180,000 year interruption in the geological record due to erosion.

It was not only the landscape that altered, but also the plant and animal life in the region – transforming the resources available to our early ancestors.

Image copyright Human Origins Program, Smithsonian
Image caption The dig site revealed evidence of climate change that oscillated from arid to wet

When the record resumes, the way of life of these early humans has completely changed.

"The speed of the transition is really remarkable," Dr Potts said. "Sometime in that [gap] there was a switch, a very rapid period of evolution."

The obsidian road

New tools appeared at this time – small, sharp blades and points made from obsidian, a dark volcanic glass.

This technology marks the transition to what is known as the Middle Stone Age, explained Dr Eleanor Scerri from the University of Oxford.

Rather than shaping a block of rock, into a hand axe, humans became interested in the sharp flakes that could be chipped off. These were mounted on spears and used as projectile weapons.

Where 98% of the rock previously used by people in the Olorgesailie area had come from within a 5km radius, there were no sources of obsidian nearby.

People were travelling from 25km to 95km across rugged terrain to obtain the material, and "interacting with other groups of early humans over that time period", according to Dr Potts.

This makes the site the earliest known example of such long distance transport, and possibly of trade.

Image copyright Human Origins Program, Smithsonian
Image caption (l to r) Hand axes, obsidian sharps and colour pigments discovered at the site

There is additional evidence that the inhabitants, who would likely have lived in small groups of 20-25 people, also used pigments like ochre. It is unclear whether these were merely practical or had a ritual social application.

Dr Marta Mirazon Lahr from the University of Cambridge said that being able to "securely date" the continuous occupation of the site using argon techniques on volcanic deposits "makes Olorgesailie a key reference site for understanding human evolution in Africa during [this period]".

Human origins

Dr Scerri, who was not involved in the studies, emphasised that they are valuable in implying that "Middle Stone Age technology emerged at the same time in both eastern and northwestern Africa."

Prof Chris Stringer from the Natural History Museum agrees.

"This makes me think that the Middle Stone Age probably already existed in various parts of Africa by 315,000 years ago, rather than originating in one place at that time and then spreading," he said.

While the behaviours exhibited at the Kenya site are characteristic of Homo sapiens, there are as yet no fossils associated with this time period and location.

The oldest known Homo sapiens fossils were discovered in Morocco, and are dated to between 300,000 and 350,000 years old.

For more on this story, listen to Science in Action on the World Service on Thursday 20:30 GMT, or catch up on iPlayer.

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