There is an alleged error in Luke 3:36. The genealogy gives an extra Cainan not found in similar genealogies, such as Genesis 11:12.
Expositor Dr. John Gill gives ample reasons why this was a copyist error.1
Gill says:
This Cainan is not mentioned by Moses in #Ge 11:12 nor has he ever appeared in any Hebrew copy of the Old Testament, nor in the Samaritan version, nor in the Targum; nor is he mentioned by Josephus, nor in #1Ch 1:24 where the genealogy is repeated; nor is it in Beza’s most ancient Greek copy of Luke: it indeed stands in the present copies of the Septuagint, but was not originally there; and therefore could not be taken by Luke from thence, but seems to be owing to some early negligent transcriber of Luke’s Gospel, and since put into the Septuagint to give it authority: I say “early,” because it is in many Greek copies, and in the Vulgate Latin, and all the Oriental versions, even in the Syriac, the oldest of them; but ought not to stand neither in the text, nor in any version: for certain it is, there never was such a Cainan, the son of Arphaxad, for Salah was his son; and with him the next words should be connected.
If the first Cainan was not present in the original, then the Greek may have read in a manner similar to the following. Remember that NT Greek had no spaces, punctuation, or lower case letters.
TOΥΣAΡOΥΧTOΥΡAΓAΥTOΥΦAΛEΓTOΥEBEΡTOΥΣAΛA
TOΥAΡΦAΞAΔTOΥΣHMTOΥNΩETOΥΛAMEΧ
TOΥMAΘOΥΣAΛATOΥENΩΧTOΥIAΡEΔTOΥMAΛEΛEHΛTOΥΚAINAN
TOΥENΩΣTOΥΣHΘTOΥAΛAMTOΥΘEOΥ
If an early copyist glanced at the third line, while copying the first line, it is conceivable that the phrase TOΥΚAINAN (son of Cainan) may have been copied there.
TOΥΣAΡOΥΧTOΥΡAΓAΥTOΥΦAΛEΓTOΥEBEΡTOΥΣAΛATOΥΚAINAN
TOΥAΡΦAΞAΔTOΥΣHMTOΥNΩETOΥΛAMEΧ
TOΥMAΘOΥΣAΛATOΥENΩΧTOΥIAΡEΔTOΥMAΛEΛEHΛTOΥΚAINAN
TOΥENΩΣTOΥΣHΘTOΥAΛAMTOΥΘEOΥ
There is some circumstantial evidence for this theory. The Septuagint (LXX) is a Greek translation of the Old Testament said to be translated by about 72 rabbis. Early copies of LXX do not have the extra Cainan in Genesis 11, but later copies postdating Luke’s gospel do have the extra Cainan.
It might seem odd to suggest that there could be a copyist error in our translations of the Bible. What is even more remarkable to me, however, is that such possible copyist errors are so extremely rare. Paradoxically, the possible existence of such an error merely reinforces how God has preserved His Word through the centuries. http://www.answersingenesis.org/articles/2009/07/06/contradictions-an-extra-cainan