The Roman Theory
This theory was first presented in 1874 by L.F.A. Wimmer and states that the runes are a result of the adaptation of the Roman (or Latin) alphabet. It is assumed that the ancient Germanic people, who came into contact with Roman culture through the invasion of the Teutones and Cimbri, were familiarized with the Roman written alphabet as early as the 2nd century B.C.E. They then adapted the Roman alphabet into the runes and put it to use, spreading it by the means of trading routes into Scandinavian countries and then eastward from there.
The one thing that we need to watch in this theory is the fact that there is little evidence of the runes near Roman lands at such a time. However, the spread of the runes into Scandinavian countries and from there eastward may mean that the adaptation of the Roman alphabet wasn’t complete until the runes had begun to spread northward.
The Indigenous Theory
First put forward in 1896 by R.M. Meyer and popularized by National Socialist Germany, this theory states that the runes were an original “alphabet.” Not only were they said to be original but they were also said to have been the groundwork on which the Greek and Phoenician alphabets were created.
This theory no longer holds much value to it due to the fact that the earliest Phoenician writings can be dated back to around the 13th or 12th century B.C.E., while the earliest runic inscription dates back to the 1st century C.E.
The Greek Theory
This theory was first stated in 1899 by Sophus Bugge and talks about how the ancient Germanic people adapted the Greek alphabet to create the runes. The theory goes that the Goths had come into contact with a cursive form of the Greek alphabet. The Goths then adapted the cursive form of that alphabet for their own use allowing the new alphabet to spread with them as they traveled.
There are problems with this theory, which have led it to be abandoned by many people. Again we see a fault in the times for this theory. The earliest the Goths would have been able to adapt such an alphabet is around 200 C.E. and the earliest runic inscription would have been earlier than that.
The North-Italic Theory
This theory by C.J.S. Marstrander in 1928 was strengthened in 1937 by Wolfgang Krause. The theory goes that the Germanic people living in the Alps came into contact with the North-Italic (or Etruscan) alphabet and adapted it. Then the Cimbri come into contact with the “new” alphabet and pass it on to the Suevi who carry the runes up the Rhine river to the North Sea, Jutland and beyond.
The only real “problem” with this scenario is that the encounter would have taken place two to three hundred before any runic inscriptions that are already dated. But this doesn’t mean that it couldn’t have happened. Items made of wood may have been carved with the runes and may have long since decayed.