You see many of the same themes crop up in various myths in the Mediterranean region. In fact, the region is rife with Miraculous births, Dying-and-rising gods, Eating the flesh of a god, and other cornerstones of the Christ myth. The reason for this should be obvious; they are concepts that are universally symbolic to people, and as stories are told between cultures, the tales are adapted to fit their own local god or gods. Early Christians are no different. It's already been mentioned how they were strongly influenced by the Roman god Mithras for their ideas of Jesus.
Honestly, I'm reading the Wiki entry and not seeing a lot of correspondence between the two narratives. All of this is arguing shades of gray: we could as easily say that the Christians plagiarized from Odysseus because he was a man who was born and lived. The Mithras correlations are more compelling, although some of them have been exposed as forgeries, and others again are simply coincidences.
But do feel free to continue posting art pictures of naked women.
Joseph Campbell explains the histories of religions in his masks of God. Many similarities between religions spring from the biology of being a social animal..so empathy. We are also a story-telling animal and the nature of stories is that they morph and build. A good story-teller can shape a pre-existing story into one that is inclined to cohere a community or to control its members or soothe their fears. Hamlet was a story that was already told. Shakespeare changed it to make it spin in one's head, unresolved.
There are also biological hot topics that find prominence in religion. Consider that the Y chromosome in a man "wants" to replicate.
The man will prefer a virgin in order to insure his off-spring carries his DNA. Like a lot of impulses, the individual rarely realizes what motivates his desires and actions but those desires find their way into his dreams like the rabies virus makes its host want to bite.
Dreams have a large impact on religions. Saint Michael went to Hell to rescue Moses in a dream and now it's part of the Catholic liturgy. It satisfies one of the holes in the concern that Moses could not have been baptized so he had to go to Hell through no fault of his own...just bad timing. Sort of a kluge solution. Religions evolve, and very rarely start over...throw out the bath water for fear of the baby going, too. The New Testament might have been intended as a start-over by claiming that all those old rituals were bogus...you just needed these new ones. But, baptism wasn't new just altered. If you are keenly interested in this topic there is a wealth of information, Joseph Campbell will get you started and you might add Paul Shepard.
When the Spaniards conquered Tenochtitlan, they build the cathedral exactly over the "Templo del Sol" (Sun Temple) and they made sure they covered all the ritual areas with the new building. The same principle applies to legends and books, new religions adjust to replaced religion's key dates and facts in order to replace them without objection.