That’s preposterous. There’s no way chickens with the best adaptation are the ones being bread; they’re in cages. Selective breeding could’ve easily developed a selection bias of large chickens that are obscenely aggressive and fight their confines.
Large chickens have certainly been bred for but this is part of the reason modern domesticated chickens are ill suited for wild life: they are too fat and too slow besides being flightless. Hens in particular have no natural defenses against predators.
