frekk said:
You're right, its not entirely clear how one developed into the other. BUT, its abundantly clear that there is a relationship (and possibly also a relationship with Minoan scripts as you mentioned). Phoenicians didn't spring into being from nowhere, alphabet in hand. Rather they were a cultural product of their area, perhaps a result of Minoan or other influences on the Canaanite coast. We DO have Phoenician texts written in Ugaritic script which predate the Phoenician text, so we know that the Phoenicians were not a preliterate people who developed an alphabet and then started writing - they were already writing when they developed their alphabet. This is not uncertain at all.
As for runes, again one cannot automatically assume that these developed spontaneously in isolation, when diffusion of many, many, many other ideas and technologies had reached this same area from the literate civilizations in the south. Presumably you're referring to Futhark, of which the earliest example is 160 AD .... it's possible that no diffusion is involved, but highly unlikely, considering Roman and other Meditteranean artifacts have been present in the UK and Scandinavia by this time for centuries. Given the date, the context, the amount of contact and trade, and the overwhelmingly obvious, visible similarity with Etruscan/Greek alphabets, it really isn't very likely it sprang into being spontaneously. It doesn't matter what it did spring from, what matters is only whether or not it was a spontaneous invention or not. At best, I think you might make the case that it was unrelated to other scripts in the manner that Braille is ... but even so, given the time period, its more or less impossible that writing was entirely unknown in the areas Futhark evolved.
Futhark is just one variation of the runic alphabet, representing the first few letters of in the same way that Alpha-beta (alphabet) does. There are other examples of runic alphabets, and earlier examples of "runelike" images which may have been part of a pre-writing (magic pictures). It is worth noting that even today, magic is still a big part of runic tradition and is connected to the way that runes were not arbitary signs, but had developed from images.
When I was studying Fine Art at university I developed a hypothesis to explain some of the similarities between different alphabets, and the fact that alphabets and writing systems have evolved in isolation on more than two occasions. Unfortunately it is not very well acepted and is more than a little controversial as it's one of those things that is difficult to scientificly prove.
The hypothesis calls for a kind of universal visual grammar (as argued for by Noam Chomsky, one of the reasons that the idea is disliked in Britian, as Chomsky is often derided by the british art world), which shapes our view of the world by the way it orders the sensory information that we recieve. When two people comunicate using an intuitive writing system (rather than a arbitrary system such as the Incan method of knots tied in a length of rope) those people are taking advantage of a shared visual grammar to decypher those signs. Later, when alphabets are developed and the original intuitive meaning of the signs is lost within an arbitrary system, that degree of shared visual gramma is not needed. (we use the intuitive visual grannar a lot today when watching movies).
There is evidence of this universal grammar, in the development of children's drawing for example, or the art of non literate peoples.
There are a few problems with this idea, not the least is why did it take so long for people to develop intuitive writing systems, as homosapiens has been around for hundreds of thousands of years, why only in the last four or five thousand years have these systems developed? Could it be that the facaulty was there all along, but it needed certain social conditions to occur before it could be exploited (for instance a large religous caste with time on thier hands to practice the magic of art)? (BTW I'm talking about universal
visual grammar being something above and beyond the universal grammar needed to understand verbal language and arbitrary writing systems, as they seem to be different things, at least based on structure).
To be honest, intuitive writing systems should be a development of social conditions in general and religion specificly. Arbitary writing systems, and alphabets should follow on from this (although they have sometimes developed on thier own as part of an administrative need, as in the Incan empire where they were needed for the running of the road network). Literature is actualy present all through the system, but is most often in the early stages linked intrinsicly with religion.
I'd probably set up the tech tree like this;
farming> divison of labour> religion
religion+ art> writing
divion of labour> administraion
administraion+ writing> alphabet
Administration is also a key part of governance which above a certain size requires writing.
The good thing is that Civ has always been flexible enough to fit to your own worldview, so you can set it up how you like.

It'd be fun to see an early scenario based on the very begining of civilisation. It'd be a great way to test out the flexibility of the civ IV tech tree...