JOEL - First of all you need to understand that what was said in the Journal of Discourses and in Mormon Doctrine are the opinions of the authors, and not necessarily revealed doctrine from God. But if we assume what they are saying is correct, Jesus was literally conceived as a result of the union of the seed of God with the egg of Mary, the same as happens with all humans now. However, none of these statements specifically describes the conception as a result of physical sexual intercourse between the body of God and the body of Mary. God knew about artificial insemination long before we figured out how to do it. I believe the "natural action" is only refering to the actual moment of conception as the seed of God unites with the egg of Mary and then developes into a baby. How God actually placed His seed in Mary is something noone can know, nor is it something we need to know. All we do know is that it was done by the power of the Holy Ghost.(Luke 1:35, Alma 7:10)
Elder James E. Talmage, a past authority of the LDS Church, has written: "That Child … born of Mary was begotten of Elohim, the Eternal Father, not in violation of natural law but in accordance with a higher manifestation thereof; and the offspring from that association of supreme sanctity, celestial Sireship, and pure though mortal maternity, was of right to be called the 'Son of the Highest'" .
The phrase "not in violation of natural law, but in accordance with a higher manifestation thereof", suggests that it was not done in the traditional way as mortals would, but by some other means we can not now understand.