"The chances of it having only happened once? Infinitesimal."

I'm not so sure. It's a rock-solid bet that that any life in the universe progresses via evolution by natural selection. It took billions and billions of tiny steps over three billion years to progress from simple multicellular organisms to our advanced civilisation. Only a tiny percentage of planets will possess suitable materials and the environmental conditions needed to drive that process. It's about as likely as a chimpanzee randomly banging typewriter keys managing to type the Bible. But it is a very big universe.