JOEL - This concept is based on a very bad interpretation of a parable Jesus told about the wheat and the tares and other scriptures.

"He answered and said unto them, He that soweth the good seed is the Son of man;
The field is the world; the good seed are the children of the kingdom; but the tares are the children of the wicked one;"(Matt 13:37-38)

Some people claim that this parable is talking about what happened in the Garden of Eden. Adam and Eve represent the good seed and the tree of knowledge of good and evil in Eden represents Satan. Eve became pregnant with Cain through the interaction(sex) she had with Satan. The tares represent the bad seed that came from Satan through Cain.
In Genesis 3:15, God says, "And I will put enmity between thee [the "serpent," or Satan] and the woman [Eve], and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel."
Proponents of this doctrine argue that if "her seed" (Eve's legitimate posterity) is a literal, flesh-and-blood race, then "thy seed" (Satan's progeny) must also be a literal, flesh-and-blood race.
Thus, two races came from Eve-one by Satan, the other by Adam. Adam's descendants, through Seth, are said to be the "holy people" who have proclivities toward righteousness and good deeds; while Satan's descendants, through Cain, have the characteristics of the father of their race.
Unfortunately this false serpentine seed doctrine is promoted by many to justify their hate and racist attitudes against blacks, Jews, and other races.

However the scripture in Genesis is very clear on how Cain came to life and completely contradicts this interpretation:

"Now Adam knew Eve his wife, and she conceived and bore Cain, and said, "I have acquired a man from the LORD." (Gen. 4:1)

But those that believe in the serpent seed doctrine claim that this scripture was not translated correctly in the King James Bible and as such they say does not support Adam as Cain's father.

However, notice how the word "tree" is used in Genesis 3:1-3:

"Now the serpent was more subtil than any beast of the field which the LORD God had made. And he said unto the woman, Yea, hath God said, Ye shall not eat of every tree of the garden? 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."

If the "tree which is in the midst of the garden" represents something other than a tree(Satan), and the fruit of the tree represents the seed of Satan, then in order to be consistant in the interpretation, shouldn't all the "trees of the garden" also represent something other than trees? Who were all those other people(trees) that were in the garden whose fruit was acceptable to eat?

Also, God said to Cain:

"If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him." (Gen 4:7)

Why would God even tell Cain of these options if He already knew that Cain was literally Satan's son and therefore would never choose to do well?

Cain can be considered a child of Satan in the figurative sense because of what he did, but our latter-day scripture makes it clear that Cain was the son of Adam and Eve(Moses 5). Of course this will not impress anyone not of our faith. Neither will the fact that Satan has no body, which would make it impossible for him to impregnate Eve.

It is not really clear in Moses 5 that Adam and Eve had children before Cain and Abel, even though in the sequence of the scriptures it does talk about them having sons and daughters before it mentions Cain and Abel.

"And Adam knew his wife, and she bare unto him sons and daughters, and they began to multiply and to replenish the earth. (Moses 5:2)

But this and all the scriptures from verses 1 to 15 seem to just be making a general statement about them having children after leaving the Garden and how they raised their children. These "sons and daughters" could have included Cain and Abel who were the first. Then starting with verse 16 it seems to go back in time to give a more detailed story of the birth of Cain and Abel.
Also, after Cain killed Abel the scriptures make it clear that Seth was born to take the place of their dead son Abel.

"And Adam knew his wife again, and she bare a son, and he called his name Seth. And Adam glorified the name of God; for he said: God hath appointed me another seed, instead of Abel, whom Cain slew." (Moses 6:2)

Why would he say this if there already were other sons and daughters who could have filled this position? So in my opinion I believe that Cain and Abel were the first, although I know there are others who might not agree with this interpretation.

LIES - Isn't it so, that the Church makes it clear that the transgression of Eve wasn't sexual but against a commandment (I think that members of the Church should know that). Can you please tell me which prophet made that known?

JOEL - This was known in the Church from the very beginning. In 1835 when the Prophet Joseph Smith began performing marriages, he declared that “marriage was an institution of heaven, instituted in the garden of Eden.” (History of the Church, 2:320).
Eve is called Adam's wife in the scriptures:

"And the rib which I, the Lord God, had taken from man, made I a woman, and brought her unto the man. And Adam said: This I know now is bone of my bones, and flesh of my flesh; she shall be called Woman, because she was taken out of man.
Therefore shall a man leave his father and his mother, and shall cleave unto his wife; and they shall be one flesh.
And they were both naked, the man and his wife, and were not ashamed." (Gen. 2:22-25; Moses 3:22-25)

If Adam and Eve were married in the Garden of Eden then the transgression they committed could not have been sexual; unless of course Eve had sex with Satan, which of course we know didn't happen.

Elder Joseph Fielding Smith also explained, “The transgression of Adam did not involve sex sin as some falsely believe and teach. Adam and Eve were married by the Lord while they were yet immortal beings in the Garden of Eden and before death entered the world.” (Doctrines of Salvation, 3 vols., Salt Lake City)