He continues in an article in the November issue Scientific American in which he discusses the possibilities with Richard Dawkins, who isn't quite as skeptical as Shermer. Dawkins argues:
In the film vignette, you implied a quite staggering rarity, so rare that you don’t expect two humanoid life-forms in the entire universe. Now you are ... pointing out, correctly, that a certain inevitability would predict that humanoids should have evolved more than once on Earth! So, yes, we can say that humanoids are fairly improbable, but not necessarily all that improbable! Anything approaching “a certain inevitability” would mean millions or even billions of humanoid life-forms in the universe, simply because the number of available planets is so huge. Now, my guess is intermediate between your two extremes ... I suspect that humanoids are not so very rare as to justify the statistical superlatives that you permitted yourself in the vignette.The argument depends on how often life has actually arisen in the universe, and I hard to find it disagree with Dawkins when considering the potentially vast number of intelligent species that could have arisen in an infinite universe.
However, I think Dawkins slightly misses Shermer's point. The way that popular culture depicts aliens - from the many humanoid species in the Star Trek and Star Wars universes to the big-eyed Greys of UFO abduction stories - is almost certainly wrong. Even if the universe holds a million planets with intelligent humanoids, the chance that humans will encounter them is vanishingly small. If we do eventually find intelligent extraterrestrial life, it's likely that they won't be anything like us. And they almost certainly won't look like this:
Related: Darren Naish at Tetrapod Zoology on "Richard Dawkins and the crappy 'humanoid dinosaurs' that just won't die" (based on Dawkins' comments quoted in Shermer's column).
Read "Will E.T. look like us? at Scientific American
Or if you want something a bit lighter, check out "Star Trek's 6 Most Ridiculous Alien Races" at Cracked.com (although in an infinite universe perhaps there really is a planet inhabited solely with individuals who appear to match the "cartoonish Italian mobster stereotype" of early 20th-century Earth - anything's possible, right?).
Image: Cantina scene from the Star Wars Holiday Special