Unfortunately, we don't have anything else to base our speculations off of. And saying it's "not valid" is simply not true. Life on Earth is the only life we know of, so that's a logical first step when making our deductions. There are many scientists out there who share my view (Phil Plait is one I know of). Yes, there might be aliens out there that are so different from us they might force us to re-evaluate the very definition of "life", but based on the existing data (it's not much when you consider it's only from our own planet, but that's the only factual base we have), if life like us happened once, then chances are that somewhere out there, on a planet similar to our own, life has developed in a similar way.Rakuen Growlithe wrote:That's where the problem lies. You're basing what a different life form might look like but using our existing life as a base.
It's only logical.