Early and modern LDS Church leaders believe and teach that Jesus was concieved in the natural way everybody was concieved; through sexual intercourse.They never verbalize that Mary wasn't a Virgin though. Instead they redefine Virgin. Apparently sex with a space colonizer isn't real sex despite the fact that the Prophet Joseph Smith said that "The Father has a body of flesh and blood as tangible as man's..." D&C 130:22 Which is probably why LDS Church leaders have admonished people about spiritualizing away Christ's conception. The real problem with this doctrine is; if Mary wasn't a Virgin as prophesied by Isaiah, then Jesus doesn't fit the prophetic requirements of the Messiah. It would make Jesus of Nazareth a false Christ.

-Adam had sex with Mary

"Adam was an immortal being when he came. on this earth he had lived on an earth similar to ours... and had begotten all the spirit that was to come to this earth. and Eve our common Mother who is the mother of all living bore those spirits in the celestial world.... Father Adam's oldest son (Jesus the Saviour) who is the heir of the family is Father Adams first begotten in the spirit World. Who according to the flesh is the only begotten as it is written. In his divinity he having gone back into the spirit World. and come in the spirit [glory] to Mary and she conceived for when Adam and Eve got through with their Work in this earth. They did not lay their bodies down in the dust, but returned to the spirit World from whence they came." -Journal of L. John Nuttall, personal secretary of Brigham Young, Feb. 7, 1877 in BYU Special Collections. Lecture at the Veil Saint George Temple

-Joseph Smith taught it

"President Young spoke of the first organization of this school by Joseph Smith the Prophet. The Word of Wisdom was given in this school. President Young said Adam was Michael the arch angel and he was the father of Jesus Christ and was our God and that Joseph taught this principle." -Wilford Woodruff Journal, Vol.4, p.288, September 17,1854

-Jesus was concieved by sexual intercourse

"There is no need to spiritualize away the plain meaning of the scriptures. There is nothing figurative or hidden or beyond comprehension in our Lord's coming into mortality. He is the Son of God in the same sense and way that we are the sons of mortal fathers. It is just that simple." -Bruce R. McConkie, The Promised Messiah, pg.468

-The Virgin birth is false doctrine

"The Father had a Son, a natural Son, his own literal Seed, the Offspring of his body." -Bruce McConkie, The Promised Messiah, pg.355

-Prophet to prophet, to prophet, the doctrine is established

"He [Brigham Young] said that our God was Father Adam He was the Father of the Savior Jesus Christ — Our God was no more or less that ADAM, Michael the Arkangel" -Pres. Wilford Woodruff, February 19,1854

-Adam is our "only God"

"Another meeting this evening. President B. Young taught that Adam was the Father of Jesus and the only God to us." -Diary of Hosea Stout, April 9, 1852, vol. 2. p. 435

-Jesus was not begotten of the Holy Ghost. The Bible is false.

"Christ was begotten of God. He was NOT born without the aid of man and that man was God!" —Joseph Fielding Smith, Doctrines of Salvation, Vol. 1:18

-Modern prophets taught it

"The Church of Jesus Christ of Latter-day Saints proclaims that Jesus Christ is the Son of God in the most literal sense. The body in which He performed His mission in the flesh was sired by that same Holy Being we worship as God our Eternal Father. Jesus was not the son of Joseph, nor was He begotten by the Holy Ghost. He is the Son of the Eternal Father!"   -Pres. Ezra Taft Benson, Come Unto Christ, p. 4

-Modern Apostles believe the early doctrine too

"Their testimony is that Mary's son is God's Son; that he was conceived and begotten in the" normal way; that he took upon himself mortality by the natural birth processes; that he inherited the power of mortality from his mother and the power of immortality from his Father-in consequence of all of which he was able to work out the infinite and eternal atonement." -Bruce R. McConkie, The Promised Messiah: The First Coming of Christ, p.472

-It was sex, plain and simple

"Christ was Begotten by an immortal Father in the same way that mortal men are begotten by mortal fathers." -Bruce McConkie, Mormon Doctrine, 1966, pg.547

-Why don't they teach that Mary wasn't a Virgin?

"As far as this life is concerned, [Jesus] was born of Mary and of Elohim; he came here as an offspring of that Holy Man who is literally our Father in heaven. He was born in mortality in the literal and full sense as the Son of God. He is the Son of his Father in the same sense that all mortals are the sons and daughters of their fathers." Bruce McConkie, Mortal Messiah 1:330

-Jesus was a "literal Son"

"And Christ was born into the world as the literal Son of this Holy Being; he was born in the same personal, real, and literal sense that any mortal son is born to a mortal father. There is nothing figurative about his paternity; he was begotten, conceived and born in the normal and natural course of events, for he is the Son of God, and that designation means what it says." -Bruce R. McConkie, Mormon Doctrine, 1966, pg.742

-Modern Prophets teach Jesus was concieved through sexual intercourse

 "The Church of Jesus Christ of Latter-day Saints proclaims that Jesus Christ is the Son of God in the most literal sense. The body in which He performed His mission in the flesh was sired by that same Holy Being we worship as God our Eternal Father. Jesus was not the son of Joseph, nor was He begotten by the Holy Ghost. He is the Son of the Eternal Father!" Ezra Taft Benson, Come Unto Christ, p. 4

 -Jesus is Adam's son

 "We Believe in Our God" by Eliza R. Snow

 We believe in our God the great Prince of His race,

The Archangel Michael, the Ancient of Days,

Our own Father Adam, earth's Lord, as is plain,

Who'll counsel and fight for his children again.

We believe in His Son, Jesus Christ..."

This hymn book was published by Brigham Young, Parley P. Pratt, and John Taylor, two of the Latter-day prophets. It was also published while Joseph Smith was alive, the Church didn't corrected it; check out the Aug. 2005 Ensign.

Sacred Hymns and Spiritual Songs for The Church of Jesus Christ of Latter-day Saints p. 375, Liverpool, 1856

"Beware lest any man spoil you through philosophy and vain deceit, after the tradition of men, after the rudiments of the world, and not after Christ. 
For in him dwelleth all the fulness of the Godhead bodily." Col 2:8-9

"And without controversy great is the mystery of godliness: God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory.” 1 Tim 3:16

"In the beginning was the Word, and the Word was with God, and the Word was God." John 1:1

"But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost." -Matt 1:20

 "Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us."  Matt 1:23