Scenario: times are hard on the African Savannah. Vegetation close to the ground has all been eaten. A creature with a slightly long neck, let's call it a proto-giraffe, can reach high leaves and so survives. Then times get harder. The high leaves get scarce. The only food is the very highest leaves that only the very tallest proto-giraffes can reach. Many proto-giraffes die, only those with the longest necks survive. Natural selection. They pass on their genes to their children. Now these animals have on average slightly longer necks than was the case in earlier generations. Evolution.
Where's the problem here? Help me out.
Let's leave the steel dome thing for now, I don't know how to respond to that.