When I began my campaign, I had not strictly defined what any of the demi-human races were like (and had no real interest in doing so). Thus, when the first player to create a dwarf asked me what dwarves in my world were like, I told him to tell me. Because he balked at the idea, I started brainstorming ideas. The one he was most interested in was James' Dwimmermount dwarf. Though this was the genesis of dwarves in my campaign, Lost Colony dwarves differ from Dwimmermount dwarves in significant ways (they are neuters, for example) — not through my doing, but rather for things said and done by dwarf players in the campaign.
When my party found out that dwarf reproduction involved building a dwarf with the possibility of coming out with a gnome, they were intensely interested in getting a gnome for the group. They even planned to fund Ahkmed in the creation of said gnome — keep shelling out 10,000gp until a gnome came out. It was then decided that it was traditional for Dwarves only to have one son.
I reasoned that any son created after the first would have a very high chance of being a Knocker (a Chaotic Dwarf). I also reasoned that it had not always been that way. This tragic story was suggested by Mr. Raggi's module The Hammers of the God. It also suggested an origin for elfin maids bound to magical weapons.
One of the hammers of The Hammers of the God is a bane weapon — it is designed to be better against a specific kind of creature. There were also murals within the module that suggested that all of the various races of the earth had cooperated in making bane weapons in order to assure peace. This peace was destroyed by the dwarves (thus, giving a nice reason for there to be antipathy between the two races).
I figured that the dwarves (under the leadership of Mär-Rune from Raggi's module) started stealing all of the bane weapons in order to make war on all of the other races. The war that ensued so tainted the dwarven race, that they can no longer make more than one son without having that taint becoming manifest in their offspring. This war also sowed the seeds for the creation of the Sons of Cyn — but that is for another day.
Unfortunately, my players decided not to pursue the clues I had laid for them to find The Hammers — but the dungeon and all of this information has been placed into my campaign and awaits exploration.
3 hours ago