In 2001, Dr Christopher Chippindale, of Cambridge University's museum of archaeology and anthropology and Dr Paul Tacon of the Australian Museum in Sydney have carried out surveys of rock art painted on cliffs in northern Australia, on ledges in South Africa and inside caverns in France and Spain.

But Tacon and Chippindale wanted to find common denominators among these creations, despite the fact that they were painted on different continents.

After careful analysis, they found only one: the 'therianthropes' - human-animal hybrids. Statues of cat-head humans, for example, were found in Europe, while in Australia the team discovered paintings of feathered humans with birdlike heads and drawings of men with the heads of fruit bats.

'Hybrids were the one ubiquitous theme we discovered,' Chippindale said. 'They belong to an imagined world which was powerful, dangerous and - most likely - very frightening.'

According to Chippin’, these rock art nasties were gazed upon by people in 'altered states of consciousness' - individuals who were either drugged or in trances.