More of "because you are a continuous chemical reaction that started 4 billion years ago". A bunch of legacy crap gets left around from the time before higher order thought when the brain - muscle interactivity was just based on feelings.
If we had all those animals, especially those around the time of the cambrian explosion to experiment on as they developed it would probably make more sense in the 'but it does' department. This is also why your math teacher wants you to show your work.
Explain the first part of this sentence.