Intelligent Design is fraught with even more difficulties, as it suggests God as one who dips His hand in every now and then to bring about the first microbial life, to bring about new forms during the Cambrian explosion, and to finally create humans after 4.55 billion years of earth, while He was doing... what exactly? According to Intelligent Design advocates, God tinkers with animal life every once in a few hundred million years or so, for reasons never made explicitly clear.