Vincent Taylor - The Historical Evidence for the Virgin Birth (1920)
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The title is a tad misleading since this isn't an attempt to prove the virgin birth and not really an examination of the fairly brief sources (basically just two canonical gospels) that could be considered evidence. Instead it's more an examination of how traditions and theology have treated this issue, presented as how it developed as intellectual history. So what he ends up with is a fairly detailed look at various approaches to the issue, exploring the Q source and alternative texts.
Taylor (1887–1968) was a Methodist scholar who taught at Wesley College in Leeds and practiced textual and source criticism. His best known work is 1937's Jesus and His Sacrifice though he wrote around twenty books. There's a good overview in Donald K. McKim's Dictionary of Major Biblical Interpreters.