The audio with Don Schrider is a good one to listen to.  One part they were talking about commercial leghorn breeding in comparison to, I think buckeyes.  The point was, how selection for different physical traits related to egg production, actually allowed for the increase in egg production to occur.  I guess you can relate that to hauling eggs in your car.  In one case you have a car with a trunk full of eggs, the next time you add a trailer so you can move more at one time.  Then the next time you find a truck with an 8’ bed and a trailer.  Now at this point you have too many eggs and you say the heck with it and hire a moving company with 18 wheelers. The owner of the 18 wheeler has lost touch with how it all began and can’t comprehend hauling eggs in your trunk and starts to dictate a lot of how the process works, to the point of cost, quality, etc..  Here, we begin the process all over again except we get to dictate what happens next.  I think that was the point,  maybe I just explained the commercialization of poultry.  Short answer is that there is a lot of good info in this website.

I saw an article on how the eggs are incubated in the Middle East, I bet there archives related to breeding somewhere.  I am sure there are some solid principles that still resonate today.