Complex sentence: Different diseases and ailments were common in prehistory than are prevalent today; there is evidence that many people suffered from osteoarthritis, probably caused by the lifting of heavy objects which would have been a daily task in their societies.
Split into simpler sentences: Different diseases and ailments were common in prehistory than are prevalent today. There is evidence that many people suffered from osteoarthritis, probably caused by the lifting of heavy objects which would have been a daily task in their societies.