Grief is characterized much more by waves of feeling that lessen and reoccur, it's less like stages and more like different states of feeling.
Human behavior is subject to the same laws as any other natural phenomenon. Our customs, behaviors, and values are byproducts of our culture. No one is born with greed, prejudice, bigotry, patriotism and hatred; these are all learned behavior patterns. If the environment is unaltered, similar behavior will reoccur.