Grieving over the dead is a trait shared by mammals. Its becoming increasingly more well known that animals can share the same capacity of suffering as humans do. I have bred dogs all my life and when a pup dies the mother will often return to the spot of death and whimper, long after their death. Seeing that can really change your perspective that we as humans are no more superior than animals. I have many times been more saddened by the death of my dogs then members of my own family.