Are 1st, 2nd and 3rd bred for those roles or selected by ability?

[ED-209]

Question in the title. I don't think it was ever specifically stated - but what do we think?

 

[Bad Thoughts]

In both Rocks and Shoals and One Small Ship, there is a discussion as to why a specific Jem'hadar was not appointed first by the commanding Vorta. In the first case, it was because of distrust. In the second, it was because it was felt the Alpha Quadrant bred would be better. In both cases, there is the suggestion that these are indeed appointments.

 

[Oddish]

Given that Jem'Hadar are essentially disposable (short lived, and their fighting skill is bred rather than trained), that would be counterproductive. If the First falls, the Second and Third are promoted. So, they would need flexibility.