It's certainly a valid hypothesis. And stronger (any?) evidence for possible life on Mars or Venus would possibly support this. With a sample size of 1, and lo

It's certainly a valid hypothesis. And stronger (any?) evidence for possible life on Mars or Venus would possibly support this. With a sample size of 1, and loose record-keeping from ~4B years ago, it's hard to tell, but we don't really know if it took life 1 day or 500M years to evolve once it was chemically/geologically viable. We do know that life was very primitive for > 1B years (not even eukaryotic, let alone multicellular). We also know that space isn't teaming with little biologically active spores from other worlds (unless it is and the government is covering it up, of course), which suggests that in the vastness of space, life doesn't really hitch rides on asteroids or comets and colonize the galaxy accidentally. And if some beings were doing this on purpose, why not send more advanced life forms or robots?