It's a bit common sense E Nomine. The reason Cain and Abel are half-brothers is because they have different father, but same mother.Cain obviously lived longer than Abel. And you won't find Cain in Adam's generation line up. (Genesis 5)Eve intructions is...Genesis 3:2-3 - And the woman said unto the serpent, We may eat of the fruit of the trees of the garden: But of the fruit of the tree which is in the midst of the garden, God hath said, Ye shall not eat of it, neither shall ye touch it, lest ye die.But she did...Genesis 3:6 - And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat.Lets go to Genesis 3:13...Genesis 3:13 - And the LORD God said unto the woman, What is this that thou hast done? And the woman said, The serpent beguiled me, and I did eat.Look at the word beguiled...beguiled = Hebrew word # 5377 nasha' (naw-shaw');a primitive root; to lead astray, i.e. (mentally) to delude, or (morally) to seduce: to beguile, to deceive utterly (infinitive).We can find that in the New Testament.II Corinthians 11:13 - But I fear, lest by any means, as the serpent beguiled Eve through his subtilty, so your minds should be corrupted from the simplicity that is in Christ.Same word for the Greek.beguiled = Greek word #1818 "exapatao" (ex-ap-at-ah'-o); To seduce wholly.That is the sexual act right there.Genesis 4:1 - And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the LORD.Notice how that is Adam saying it, not God.And Adam only had one wive.Lovest ye in Christ Yahshua our Lord and Saviour.P.S. This is a shorter version of what Kriss gave the link.