If you are interested in these issues a great book to read is called "Rare Earth:Why Complex Life is Uncommon in the Universe" by Peter Ward and Donald Brownlee

If you are interested in these issues a great book to read is called "Rare Earth:Why Complex Life is Uncommon in the Universe" by Peter Ward and Donald Brownlee. They make a convincing argument (to me anyway) that bacteria and simple life forms are probably common in the universe but animals and complex life with intelligence might be exceedingly rare. We, quite possibly, could be the only intelligent life in the universe.