I feel confident that most visitors to this site, understand the essential conflict at the heart of Christianity. How could Jesus be fully human and simultaneously be a divine being who descended (supposedly, some thing Jesus specifically claimed to be) from heaven?
As Jws we may have solved this tricky point by saying that Yahweh transferred the life of Jesus into Mary's womb, and so Jesus was born fully human.
But if we remove the blindfold of faith, we immediately 'see' the problem. In our contemporary view of the reproductive process, we can be certain that there is a female 'egg,' that is fertilised by male sperm. No sperm, then no baby. Of course, an all-powerful Yahweh who is thought to have designed the reproductive process, could be seen as altering the process to achieve his goal of transferring Jesus from heaven. But consideration of that possibility introduces some additional complexities.
We also now understand the role of genes. Both mother and father contribute genetic information to the newly fertilised egg, thus making the resultant child the off-spring of both parents.
So if Yahweh creates a new 'perfect' set of genes that somehow 'holds' the 'life' of the heavenly Jesus as the 'father's gene set, then can Jesus be fully human? Surely, to be fully human, the human Jesus would require a full set of human genes, thus being in Adam's lineage, which you will recall, is precisely how Luke describes Jesus, as the eventual 'son of Adam, son of God.'
But, doesn't that mean that Jesus bore Adam's genes? So how then can he be perfect, without sin?
What does this mean? For an answer we have to forgo the usual Christian view of the Bible as 'authored' in some mysterious way by God and see it for what it is, the product of human believers who set down this story in fully human terms, that is, they tell the story according to the way they understood that babies were made.
Andrew Lincoln, a scholar at the University of Gloucestershire, argues that the gospel authors would have believed something like this:
Their understanding of conception, shaped by a patriarchal culture, would have been some variation of the dominant Aristotelian theory. On this view, the male semen provides the formative principle for life. The female menstrual blood supplies the matter for the fetus, and the womb the medium for the semen’s nurture. The man’s seed transmits his logos (rational cause) and pneuma (vital heat/animating spirit), for which the woman’s body is the receptacle. In this way the male functions as the active, efficient cause of reproduction, and the female functions as the provider of the matter to which the male seed gives definition. In short, the bodily substance necessary for a human fetus comes from the mother, while the life force originates with the father.
Not very scientific, but an explanation that prevailed for a long time.
From that unrealistic understanding point of view, Jesus could have been fully human - i.e. the bodily substance supplied by Mary, but with Yahweh supplying the lifeforce.
The result - a perfect human, without Adam's genetic structure, because they, the gospel author's, knew nothing about genetics. In fact if Yahweh inspired the gospel authors to write, then he also knew nothing about genetics. But that is also clear in the very first Biblical account.
If you'd like to follow up on this, the Biblical Archeological Review offers this study, from which I have drawn some thoughts: