The virgin birth

After referring in chapter 20 to our dependence on God for salvation, in chapter 21 Irenaeus seeks to defend the doctrine of the virgin birth:

Amongst the arguments he uses are:

1) The priority of the Septuagint version of the OT, the weakness of which I have already commented on when discussing Justin.
2) If Jesus was truly the son of Joseph, then he could not be king, as Joseph descended from the discontinued line of Jehoiachim.
3) For Jesus to truly recapitulate what Adam did, he had to be born without a human father as was the case with Adam