I love cage eggs because I know they should be clean and fresh and laid by healthy happy hens. I always go for the cheapest cage eggs because they usually have the fastest turnover so most likely are the freshest on the shelf.
Gallus gallus ( the domestic fowl ) has been around a long time i.e. the domesticated variety. They have a similar range of varieties as the domestic dog except much more colorful. From the tiny bantam to the giant meat bird cockerel - all shapes and sizes.
Cage hens as a selected genetic variety has only been around since about 1960 or later. The farmer put his free ranging chickens in his new cages. He got more eggs and used less food but got a lot of new problems as well. The hens were nervous and didn't like to be too close so fighting broke out with vent pecking a problem.
The farmer wasn't going back to his old ways so he changed his stockmanship to adapt to the new method. Beak trimming was introduced to prevent vent pecking. Optimum stocking densities were worked out. Cooling systems to counteract heat waves and closing sheds to keep them warm was adopted.
The most important development in my opinion was the specific breeding of traits into the bird to help it adapt to life spent in a reduced area. Hens are now much more placid - they don't want to fight as much. Less energy is spent jumping around - no doubt the instinct to dust bath and flap their wings can be bred out as an unnecessary activity for a life spent free of parasites. The ability to change the hen by selective breeding to suit life in a cage is in no doubt - one only has to look at the pekinese breed of dog to realize the power of selective breeding - hard to believe its ancestor was a savage wolf.