From the discovery.com article:
Earth-like planets have relatively short windows of opportunity for life to evolve, making it highly doubtful intelligent beings exist elsewhere in the universe, according to newly published research based on a mathematical probability model.
Given the amount of time it has taken for human beings to evolve on Earth and the fact that the planet will no longer be habitable in a billion years or so when the sun brightens, Andrew Watson, with the United Kingdom’s University of East Anglia in Norwich, says we are probably alone.
Earthlings overcame horrendous odds — Watson pegs it at less than 0.01 percent over 4 billion years — to achieve life. The harsh reality is that we don’t have much time left.
Read the rest of the article here.