It's not a matter of being "lowest" animals, but "unclean" and is part of their religious doctrine. (After all, we don't eat dogs either, usually.)
In the old testament, there is a story of an agreement between God and Abraham about behavior of the Hebrews, including rules of what can and cannot eat. This "cannot" includes pork, as well as other foods, like shellfish, dairy and meat together, etc. It's called the "Covenent of Abraham" and if you recall the Indiana Jones movie, well, that's what was supposed to be in that fancy box - the original of this agreement between God and Abraham.
Anyway, both the Christian and Muslim religions are derived from the same group of people - the Hebrews, with Jesus being the final prophet (or son of God) of the Christians, and somewhat later, Mohammed being the final prophet of the Muslims. The Muslims kept the dietary rule against eating pork, the Christians did not. The earlier book (Old Testament) of the Bible is the same and is taught in all three religions, including Genesis (Adam & Eve, story of the flood, etc.); Judaism, Christianity & Islam.
I'm not familar enough with Koran to know whether Mohammed kept the other dietary laws of the Hebrews, or if it was more of a cultural tradition that was reinforced by Mohammed or what. I'll have to look that up, because I'm curious.
There is also the scientific bent of the dietary law against eating pork, and that is that both the Hebrews and the Arabs (which both are descended from Abraham according to legend) were nomadic people, and that it is just simply impossible to keep pigs for food under nomadic conditions and adding them as a food source might have plain been detrimental to their lifestyle. Cattle and sheep can be herded along with the family as it travels, pigs aren't really suited for that. Also, they require higher quality forage than cattle and sheep or goats.
Anyway - it's a religious thing and has nothing to do with the animals intelligence. Pigs are considered "unclean" according to their religion. I know Jewish people will not eat them, but I think Muslims don't even want them anywhere nearby, being unclean alive as well as a food source.
Just to say, I don't actually follow any of these religions, but I find it interesting since I live around so many people that do.
Fawn