Theories regarding the birth of Jesus Christ range from scientific hypotheses attempting to explain the conception to divine intervention. Since the first century, A.D., scientists and religious scholars alike have analyzed the birth of Jesus Christ and have debated its details and its merit.
One theory that explains how a virgin conception may have occurred purports that, while Joseph and Mary's relationship had not yet been fully consummated, they may have shared an intimate moment that led to Joseph having an emission. That emission, perhaps taking place in close proximity to Mary, somehow made its way to Mary's reproductive organs, thus fertilizing an egg.
Another theory, perhaps less plausible but more scientifically supported, involves what is known as testicular feminization. Biologically, Mary may have been born male but had ambiguous reproductive organs due to a genetic mutation that caused her body to be insensitive to testosterone. Though this would have likely rendered her sterile, she could have spontaneously become pregnant with the fetus developing yet another genetic mutation that reversed the condition that caused Mary's body to become testosterone-resistant so that Jesus would have developed as a male.
It is possible to poke holes in most if not all the theories surrounding the mystery of Jesus' conception and birth. Of course, one theory that has never been debunked and is most widely accepted among Bible-believing Christians is that the DNA and genetic material of Jesus was formed by the hands of God, and Mary was chosen as the surrogate.