Ancient humans who took a leap forward in stone tool technology 1.75 million years ago may have been budding musicians, research suggests.
The brain circuits that led to two-sided tools and weapons such as hand-axes and cleavers are the same as those activated when playing a piano, a study has shown.
The switch from simple flake and pebble technology known as "Oldowan" to more sophisticated "Acheulian" tool know-how is considered a hugely important step in human evolution.
To investigate what brought about the change, British and US scientists conducted brain scans of volunteers as they learned to make Oldowan and Acheulian tools.
They found that Acheulian tool manufacture required a combination of visual memory, hearing, movement awareness and action-planning - all essential ingredients of being a musician.
Professor John Spencer, from the University of East Anglia, said: "Our findings do not neatly overlap with prior claims that language and stone tool production co-evolved. There is more support for the idea that working memory and auditory-visual integration networks laid the foundation for advances in stone tool-making.
"It is fascinating that these same brain networks today allow modern humans to perform such behaviours as skilfully playing a musical instrument."
People living 1.75 million years ago had not yet developed any kind of sophisticated language, so the evolution of language circuits in the brain is not thought to have helped them upgrade to Acheulian tools.
The study, published in the journal Nature Human Behaviour, used an advanced form of brain scan called functional near-infrared spectroscopy (fNIRS) to track the volunteers' neural activity in real time.
Fifteen of the 31 participants learned to knap stone by watching videos accompanied by verbal instruction. The other 16 acquired the skill using the same videos, but with the sound turned off.
Study leader Dr Shelby Putt, from the Stone Age Institute in Indianapolis, US, said: "This work offers novel insights into prehistoric cognition using a cutting-edge neuro-imaging technique that allows people to engage in complex actions while we are measuring localised brain activity.
"The study reveals key brain networks that might underlie the shift towards more human-like intelligence around 1.75 million years ago. We think this marked a turning point in the evolution of the human brain, leading to the evolution of a new species of human."
US co-author Professor Robert Franciscus, from the University of Iowa, said the evolution of modern intelligent humans remained a "great mystery".
He added: "We discovered that the appearance of a type of more complexly shaped stone tool kit in the archaeological record marked an important cognitive shift when our ancestors started to think and act more like humans rather than apes."