tumbleweed41
Resident Liberal Hippie
wait. So longer appendages than turn into wings, which are covered in feathers, and fly away?
The offspring of a creature that has a genetic propensity towards a longer appendage, for example, a longer neck, may have a better chance at survival by being able to reach the leaves on the trees that the others of its herd cannot.
Since it survives longer, and is healthier than the others in the herd, it breeds more often and more successfully.
Thus passing on the "Long neck gene" to its offspring.
After a few generations, the "Long Necked" offspring are the majority in the herd, as they are better able to survive. They are also better able to see predators from their greater height.