What numsgil said. Plus, the dna is very very cluttered and disorganized, like evolved DB code. But when the genes are expressed, everything comes together. Also, to any creationists out there, even humans are extremely inefficient and chaotic in design. It just so happens that any "quick fix" or minor improvement that could have been made in our DNA to improve our efficiency has already been made. Its become almost impossible for any mutation to create improvement, and thats why it slows down. Its like trying to build a bridge over a massive valley by tossing twigs and hoping for them to come together.