section_path: Society and culture/Cultural references
section_name: Cultural references
paragraph_text: Cultural references
  
  The ancient Greek dramatist Euripides (5th century BC) describes the multiple-headed mythological monster Hydra as having a regenerative capacity which makes it immortal, which is the historical background to the name of the biological genus Hydra. The Book of Job (c. 6th century BC) describes the human lifespan as inherently limited and makes a comparison with the innate immortality that a felled tree may have when undergoing vegetative regeneration:
  
  A man's days are numbered. You know the number of his months. He cannot live longer than the time You have set. So now look away from him that he may rest, until he has lived the time set for him like a man paid to work. For there is hope for a tree, when it is cut down, that it will grow again, and that its branches will not stop growing.