Complex sentence: Vitalism is an ancient doctrine found throughout many ancient cultures, a pure vitalistic doctrine however can be traced back to Galen of the second century, a physician who became a surgeon for gladiators at Pergamum.
Split into simpler sentences: Vitalism is an ancient doctrine found throughout many ancient cultures. A pure vitalistic doctrine, however, can be traced back to Galen of the second century, a physician who became a surgeon for gladiators at Pergamum.