Atheists routinely ridicule the Bible on this one. But nowhere does the Bible say that putting striped sticks in the water physically caused the animals to have striped and spotted off-spring.
In many miracles in the Bible, God required people to go through some token action. Moses was instructed to hold his staff over the Red Sea before God parted the waters. Naaman had to dip himself seven times in the Jordan River before God would cure his leprosy. Joshua and the Israeli army had to walk in circles around Jericho and blow on trumpets before God destroyed the walls of the city. Etc. I have never heard anyone saying that they suppose that this means that taking a bath cures leprosy or that walking in circles makes buildings collapse. Rather, the principle is that God does not allow people to just sit back and sip on champagne while God performs miracles to pull their feet out of the fire. When there is something people can do to help themselves, he expects them to do it. And when there is nothing that people can do to help themselves, he still requires them to perform some token, symbolic action.
I presume that Jacob's putting the striped sticks in the water was in the same category. It did not cause the animals to be born spotted. It was just a token action that God required of Jacob before God would perform a miracle for him.