It is not that animals are irrational, but my point is that their rationality is entirely different from that of ours. Also rationality gets evolved with time.
Draconian laws and the blind belief in the God were the existed normalities in the archaic Greece. There was a time when the widow wife would get killed with her deceased husband. People believed these customs to be rational. Now a complete evolution has been happened.
Yes, I always prefer to stick with the best option available at the time. As of now it is science which is far superior to any religion. One day, if I get to see the real God, I won't hesitate to believe in him/her. Now I have no reason to believe in that concept. I believe in one less god than the theists!