God created man and put him in the Garden East of Eden. In the garden there were no sin or sickness, and there were abundance of food (fruit, herbs).

Genesis 2:16-17 (KJV)

And the Lord God commanded the man, saying, Of every tree of the garden thou mayest freely eat: But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.

Eve became rebellious against what Adam told her what God had said after she listen to the snake (the Devil) and she gave Adam to eat as well.

What is sin?

The Bible defines sin as the breaking, or transgression, of God's law (1 John 3:4). It is also described as disobedience or rebellion against God (Deuteronomy 9:7), as well as independence from God.

The Greek word for transgression in 1 John 3:4 is anomia, meaning lawlessness (law breaking). The word for sin is hamartia, which literally means “missing of the mark” (Vine’s Expository Dictionary of Old and New Testament Words, 1997, pp. 1045-1046, 1161).

The beginning of Sin

Sin had its beginning with Lucifer, probably the most beautiful and powerful of the angels. Not content with his position, he desired to be higher than God, and that was his downfall, the beginning of sin (Isaiah 14:12-15).

Be like God

The essence of the problem stemmed from the human desire to be like God. All sin, therefore, has its roots in idolatry—the attempt to put something or someone in the place of the Creator. Most often, that someone is one's own self.

Inheritance of Sin

Since that time, sin has been passed down through all the generations of mankind and we, Adam’s descendants, have inherited sin from him. Romans 5:12 tells us that through Adam sin entered the world, and so death was passed on to all men because “the wages of sin is death” (Romans 6:23).

The apostle John defines sin (the missing of the mark) as transgression (lawlessness, law-breaking). So, the Old Testament and the New Testament words define sin as being an offense and rebellion and off the mark, all of which violate the law.

This was the origin of sin, illness and poverty for the human race.

Ref.:
http://lifehopeandtruth.com/
http://www.gotquestions.org/
http://christianity.about.com/