They're gray, big-eyed, and smoother than a buffed Maserati. They're aliens à la Hollywood. Lacking noses, ears, hair, and a sense of humor, these short-statured creatures are omnipresent in sci-fi films and TV.
Not surprisingly, many members of the public assume that if we ever interact with real extraterrestrials, they'll probably resemble these colorless critters. Indeed, if you look at the drawings of aliens made by people who believe that Earth is under saucer attack, you'll quickly note that most of these invaders fit the Tinseltown mold.
But you have to admit: the grays are highly anthropomorphic. They look so much like us, if a squad of these cosmic beings moved in next door, they'd eventually be hit up for dues by the homeowners association.
In a movie it's often important to have aliens whose gestures and facial expressions can be "read" by humans. And in the days before sophisticated computer animation, most extraterrestrial bit players were guys in rubber suits. Such practical considerations forced Hollywood's hand when it came to aliens -- they look like us for good reasons. Logistical reasons.
In fact, a few biologists think that Hollywood may, by accident, have it right. They argue that Homo sapiens actually conforms to some sort of optimal design for a sentient species. Convergent evolution, a well-known selection mechanism ensuring that both dolphins and barracudas are built like torpedoes, will constrain intelligent aliens to have a vaguely human form.
But come on! Are two eyes, four appendages and an upright posture really essential for any creature that can ace the galactic SAT's?
Maybe not. In fact, I'd venture that any aliens we ever detect or (less likely) encounter will look quite different than this self-referential stereotype.
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