Answer:
Let’s expand to real traits. What determines the subtle shape of a bone, or having five finger buds that make four-boned fingers (the first bone is part of the palm, but one winds up only making two bones (the thumb) that isn’t part of the palm. All five have various muscle attachments passing under the wrist and attaching to specific points along the forearm. And don’t forget that the thumb has extra muscle at the base of the palm.
Each and every detail of making this marvelous structure depends on specific signaling proteins during gestation. How much of a protein exists translates into how far a bud is from the edge, and which edge - - pinky on one edge, thumb on the other. As a general principle, every blood vessel, bone, organ, muscle, tendon, tooth bud, and I’m just scraping the surface here, takes a shape that is pre-programmed by specific proteins, made by specific genes, in a subtle “how much of this specific protein is nearby” dance with thousands of proteins that interact in a mind-blowingly sophisticated dance.
Creationists refuse to accept that six hundred million years is enough time to evolve something so utterly marvelous, especially when they misunderstand that evolution doesn’t happen in discrete steps, it oozes.
Species-level change happens that slowly.
It oozes.
And 600 million years after that chordate animal with four fins, each having one (two?) long stiff bones and five twig-bones on the end, today we have bats and chimpanzees and homo erectus. Or as Barbra Striesand sang in one of her early numbers (in a child’s voice) “Lions and tigers and bears, Oh my!”
With a huge vocabulary, developed very very slowly over hundreds of millions of years, genes can express blueprint-level information, and all of it based on proteins.
