Why do chickens & turkeys have white meat & dark meat?

Other birds that we eat, such as quail, duck or pigeon, have all dark meat.  Chickens and turkeys are among a small group of birds with white flesh on the breasts and wings.
Birds have two types of muscle fibers; red and white.  Red muscle fibers contain more myoglobin, a muscle protein with a red pigment.  Muscles with a high amount of myoglobin are capable of much longer periods of work and stress than white fibers.  Thus, you can guess which birds are likely to have light fibers by studying their feeding and migration patterns.
Most birds have to fly long distances to migrate or to find food, and they need the endurance that myoglobin provides.  All birds that appear to have all white flesh actually have some red fibers, and with one exception, all birds that appear to be all dark have white fibers.  But the hummingbird, which rarely stops flying, has pectoral muscles consisting entirely of red fibers because the pectoral muscles enable the wings to flap continuously.

Other birds that we eat, such as quail, duck or…