What is the oldest source that people knew for sure what makes a woman pregnant?
For such a source I understand that that the author knew what a man and a woman did 9 months before giving birth and that this act was the direct reason for a child. It is enough it is said "they slept together". Pornography would be accepted, if the connection between the act and insemination is said. It is not acceptable if child was some "divine gift", "blessing of Zeus" etc.
I think it would be very old as shepherds would know how to make their herds larger.
The oldest I could find is a Holy Bible, in Genesis Chapter 4 verse 1 and then 17:
And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the LORD. (...) And Cain knew his wife; and she conceived, and bare Enoch (...)
If somebody could explain if "knew his wife" means "had a sexual relationship with her". If not, we can go further (Chapter 6 verse 4):
There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
And Lot went up out of Zoar, and dwelt in the mountain, and his two daughters with him; for he feared to dwell in Zoar: and he dwelt in a cave, he and his two daughters. And the firstborn said unto the younger, "Our father is old, and there is not a man in the earth to come in unto us after the manner of all the earth: Come, let us make our father drink wine, and we will lie with him, that we may preserve seed of our father." And they made their father drink wine that night: and the firstborn went in, and lay with her father; and he perceived not when she lay down, nor when she arose. And it came to pass on the morrow, that the firstborn said unto the younger, "Behold, I lay yesternight with my father: let us make him drink wine this night also; and go thou in, and lie with him, that we may preserve seed of our father." And they made their father drink wine that night also: and the younger arose, and lay with him; and he perceived not when she lay down, nor when she arose. Thus were both the daughters of Lot with child by their father. And the firstborn bare a son, and called his name Moab: the same is the father of the Moabites unto this day. And the younger, she also bare a son, and called his name Benammi: the same is the father of the children of Ammon unto this day.
The Wikipedia says that the Book of Genesis is ca. 6-5 century BC:
This leaves the question of when these works were created. Scholars in the first half of the 20th century came to the conclusion that the Yahwist was produced in the monarchic period, specifically at the court of Solomon, and the Priestly work in the middle of the 5th century BC (the author was even identified as Ezra), but more recent thinking is that the Yahwist was written either just before or during the Babylonian exile of the 6th century, and the Priestly final edition was made late in the Exilic period or soon after.
Are there any other, older sources confirming that people knew where children did come from?
(all Bible citations from KJV)