The history of solo diving stands in stark contrast to the relatively new concept of buddy diving that was developed for recreational diving in the early to mid-20th century. Artifacts dating back some 4,500 years provide evidence of solo diving for food and commerce by the ancient people of Mesopotamia. There are written accounts from 2nd century BC that describe commercial sponge fishing, including notes about sponge divers, their lifestyle and fear of predatory sharks. In 350 BC, Aristotle wrote about "an 'elephant nose-like tube' that allowed sponge fishermen to breathe during diving", and in 8th–6th century BC, there are references to solo diving in the writings of Homer.