Prophets Don't Know Everything
Christians denominations all teach that Christ will come to earth again soon. But despite the occasional flourish to the contrary, nobody knows exactly when that will be. If you ask the president of the LDS Church when Christ will come, he'd probably tell you "I don't know" or "When he gets here." For whatever reason, that's the way God wants it to be.
Prophets don't know everything--on purpose.
Joseph Smith once prayed about the answer to this question. This is the answer that he received:
Joseph, my son, if thou livest until thou art eighty-five years old, thou shalt see the face of the Son of Man; therefore alet this suffice, and trouble me no more on this matter.
This didn't help him understand the answer to his question any more than before.
I was left thus, without being able to decide whether this coming referred to the beginning of the millennium or to some previous appearing, or whether I should die and thus see his face.
Some people will tell you that they are sure that the earth and everything on it came about without any help from evolution. If you ask an LDS Prophet, he will tell you that he doesn't know the answer to this question. Why, because almost nothing has been revealed about the matter. What has been revealed is this:
The Church of Jesus Christ of Latter-day Saints...declares man to be the direct and literal offspring of deity...Man is a child of God, formed in the divine image and endowed with divine attributes.
Our mission is to bear the message of the restored gospel. Leave [science] which has [nothing] to do with the salvation of the souls of mankind, to scientific research...
Evolution and Mormonism: A Quest for Understanding, pages 9-10
It turns out that saying "I don't know" is also simply a matter of patience. Eventually we will know all things--when God chooses to reveal them.
Yea, verily I say unto you, in that aday when the Lord shall come, he shall breveal all things—
Things which have passed, and ahidden things which no man knew, things of the bearth, by which it was made, and the purpose and the end thereof—
When will we know all things? Sometime following Christ's return to earth. When will that be? Like I said before, "I don't know!!!" ;-)