Different ancients believed different things. Some believed women provided "seed" to the embryo, two-seed theory. Others believe women provided "ground" for the seed to grow in. However, in the patriarchal society of the time, the one-seed theory was the most common belief. (In fact, even the two-seed theorists thought that the male portion was "stronger" than the female portion.) The most influential was probably Aristotle who, advocating for a one-seed theory, wrote:
"If, then, the male stands for the effective and active, and the female, considered as female, for the passive, it follows that what the female would contribute to the semen of the male would not be semen but material for the semen to work upon. This is just what we find to be the case, for the catamenia have in their nature an affinity to the primitive matter." - The Generation of Animals
After making several disparaging remarks about women, Aristotle goes on to describe the roles of men and women in reproduction, where the male plants the "seed" in the "ground" of the woman which enables the seed to grow. Aquinas (who was heavily influenced by Aristotle) later echoed this in his Summa Theologica. This line of reasoning continued well into 1700s, especially for those most strongly influenced by Aristotle.
It also is reflected both in the Biblical narrative (where, with very rare exception, it is always the lineage of the man that matters) and extra-Biblical writings. (See Gospel of Thomas.)
This flawed understanding of biology is also important if one wants to fully understand what the Incarnation via the virgin birth meant to those in the early Church; it was God's seed (via the Spirit) that implanted Mary, making Jesus (in every sense) the Son of God. It was Mary who, being human, gave flesh to Jesus, making Him the Son of Man. The miracles were not solely (or even primarily) to be proofs that Jesus was the Messiah; the miracles were to tell us something about the nature of God and His Kingdom.
Disclaimer: This is a topic that I am still learning a great deal about, so the previous statements are not a thorough (or maybe even adequate) treatment of the subject.