Animals would probably never have been created. The nucleus is important for storage of DNA, and for the formation of mRNA to be used to synthesis proteins. Without a nucleus, we could not survive as animals, as the nucleus separates processes such as DNA translation and transcription, which if not separated could cause problems. If we had no nucleus, we would just be single celled bacteria (bacteria do not have a nucleus as their DNA is stored differently, but in such a way that it could not support animal life).