Yes, it's worked for 6,000 years in the wild, but many breeds don't bother with it. 'Modern' doesn't neccesarily mean bad at brooding. Actually, two of the newest breeds are some of the best in the world (they haven't beat the wild chicken, though). The Boxwood and the Bow Lake have been bred for nothing else but solid brooding abilities. Likewise, Leghorns, Minorcas, and especcially Hamburgs are very old, but they have no broodiness in any sense of the word.Makes sense. I guess most of my doubts stem from 2 things.
Everything that is needed to raise a chick. From keeping the egg at 99.5 degrees, to turning the eggs, to helping once they hatch, to keeping them warm after they hatch to feeding them. Granted the hen can do most of this, I just wondered if modern chickens would. Thought maybe it's been bred out of them.
'Modern' chickens as you put it are the result of bad stewardship when it comes to your point about predation. In good cases (the result of proper stewardship, or wilderness), there would be a mother hen and a cock with the chicks until they fully mature -- predator comes, mother and chicks hide, cock beats the tar out of the predator or lures it away. Most chickens you find nowadays are too stupid to do that. And it's hard once the chickens get to that lack of mentallity, to teach it to them is very hard.
And finally, you are right about climate. Chickens are very tropical animals.The handful of the hardiest breeds in the world (Finnish, Icelandic, Ushanka) may be the only ones that can survive a canadian winter without protection. Almost all the others need some amount of shelter, ranging from little in the hardiest breeds, to large, very hot shelters in say, Junglefowl or Asils.