[Certainly human interaction is necessary, but God creates every human being by His action. It is not as though God is saying "Oh, it looks like Brian and Denise just had sex again. Hey, and look, an egg got fertilized this time! Yahoo! I get to make another baby!"]
Benjamin, I certainly don't deny secondary causes. If my wife and I don't have sexual relations, no child will be conceived (unless God works supernaturally). If my wife and I do have sexual relations, and she is fertile, then she may conceive a child. What's the difference between whether a child is conceived or not conceived? Is it simply the providence of God that the path for the sperm to the egg is open, that the sperm is able to fertilize the egg, the zygote attaches to the uterine lining, etc.? Or does God "do something" that causes my wife to conceive a child as opposed to not conceive a child? (What that "something" may be, I'm not sure). God speaks in very personal terms about certain people having purposes before they were conceived, e.g., Jacob and Esau, Jeremiah, Paul, etc. Was God personally involved in the conception of these children, or as Alan says, is it simply part of God's ordinary providence? A sampling of passages from Genesis:
"Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the Lord" (Gen. 4:1).
"And Adam knew his wife again; and she bare a son, and called his name Seth: For God, said she, hath appointed me another seed instead of Abel" (Gen. 4:25).
And Sarai said to Abram, “Behold now, the LORD has prevented me from bearing children. Go in to my servant; it may be that I shall obtain children by her.” And Abram listened to the voice of Sarai. (Gen. 16:2).
15 God also said to Abraham, “As for Sarai your wife, you are no longer to call her Sarai; her name will be Sarah. 16 I will bless her and will surely give you a son by her. I will bless her so that she will be the mother of nations; kings of peoples will come from her.” (Gen. 17:15-16).
"Abraham prayed unto God: and God healed Abimelech, and his [Abimelech's] wife, and his maidservants; and they bare children. For the Lord had fast closed up all the wombs of the house of Abimelech, because of Sarah, Abraham's wife" (Gen. 20:17-18).
"When the Lord saw that Leah was hated, He opened her womb...And Leah conceived, and bare a son" (Gen. 29:31-32).
"God remembered Rachel, and God hearkened to her, and opened her womb" (Gen. 30:22).
In what sense did God give a son to Abraham and Sarah? In what sense did he close the womb of Abimelech's wives? These passages seem to describe a level of interaction that is beyond what I would consider the usual providence of God. If so, is that interaction how God normally operates in the conception of a child? Or are these the exceptions?