Many features of life either exist or they don’t. A cold-blooded creature like a frog is far different from a warm-blooded animal like a giraffe. Some time in a supposed evolutionary development a cold-blooded reptile switched over to being warm-blooded. Other examples: non-life to life, gills to lungs, non-flying to flying, mammals to whales, and special valves in the neck of the giraffe.