Many Christians believe that evil is the result of Adam and Eve's disobedience to God. In the Garden of Eden, Adam and Eve ate the forbidden fruit. God punished Adam and Eve for their actions, and the punishment was to endure suffering in life. This is known as 'the fall'.
Some Christians believe that all people inherited the tendency to sin from Adam and Eve. This belief is called original sin. According to this belief, all humans are born with a tendency towards evil and the ability to cause suffering.
In Genesis it states:
...the intent of man's heart is evil from his youth.Genesis 8: 21
Most Christians also believe that as well as a power for good (God) there is also a power for evil. Christians refer to the power for evil as Satan or the Devil. Satan is traditionally thought to have been an archangel who disobeyed God and so was thrown out of heaven.