Science can only tell us that the egg came from the chicken and the chickens came from the egg. But common sense tells us the cycle must have begun somewhere. No science, just common sense. Walking, now that is an interesting example, since humans seem to have an instinctual knowledge of walking. A child does not need to see adults walk in order to learn how.
Blind kids learn to walk too.
And a bird, hatched in isolation, can still fly. Though you, sir, seem to have considered every angle, many have not. While I assume there is a God, you assume there is not. Since neither of us knows for sure, we both must begin with assumptions. And if God is the Creator of humans, it stands to reason that He is not human.