Don't believe people when they say rubbish like this: Because they are so complicated, they are unlikely to have evolved twice. It's not like that comple

Don't believe people when they say rubbish like this: Because they are so complicated, they are unlikely to have evolved twice. It's not like that complexity has spontaneously come into existence, it's the result of normal evolutionary processes which give rise to complexity of all sorts all the time. If you ask biologists about this, most would agree there is nothing inherently improbable about the evolution of any known cell type. Of course that doesn't mean those processes wouldn't produce a completely different organism on another world, but chances are this organism would have to solve similar problems as the ones here on Earth. The need to process information and react to it in some way is not unique to our world in any way. > So if neurons did evolve twice Looking at all the systems organisms are using to carry information (not just neurons, but all kinds of chemical signaling) suggests that these systems perform a very basic and ubiquitous role in all ecosystems. Even if the assertion about neurons was true (which it most certainly isn't), claiming all of our biological information-passing systems as special and "unlikely to evolve twice" is stretching an implausible proposition even further. > it is unlikely they are the Great Filter It's unlikely anything within biology is the Great Filter, but the thing at the beginning of biology might be a candidate: it's unclear how probable the formation of a simple cell from non-biological material is. My personal hunch is that the Great Filter might really be a combination of factors, both local to us and global, and abiogenesis _might_ be one of those that globally lower the odds for life significantly.