In science fiction movies and TV shows, intelligent aliens are usually the same basic shape as humans: two arms, two legs and a head. But why would creatures that evolved on a completely different planet look so similar to us? We asked some experts, and they told us the most likely explanations for humanoid aliens.
Top image: Artwork by Wayne Douglas Barlowe
The truth is, aliens tend to look like us in science fiction for a couple of basic reasons: budget, and relatability.
"Most aliens in SF are humanoid because humans produce SF," says Michael H. New, an Astrobiology Discipline Specialist at NASA. "While we are interested in the 'other,' our conception of otherness is often limited."
And a lot of experts firmly believe that aliens would not look at all like humans. For example, Stephen Jay Gould claims that life that evolved elsewhere would look totally different from us — and in fact, if you "reran the tape" from the beginning of life on Earth, you wouldn't end up with humans on this planet either. The emergence of humanoids on Earth is a totally random event that was a fluke, even with the exact conditions that we arose from.
But let's say that we do meet aliens, and they turn out to be bipeds with a roughly human-like shape... how do we explain that?
This is the most common explanation for creatures that look sort of like us turning up all over the universe. Either humanoid aliens spread their DNA across the galaxy to give rise to creatures in their image, or the DNA just spread through the galaxy on its own, on asteroids and stuff.
Star Trek: The Next Generation reaches for this explanation in the episode "The Chase," pictured above. And it's the centerpiece of the recent movie Prometheus, as well.
"I'm of the strong opinion that if humanoid aliens exist, they must have some genetic heritage in common with human beings," says Mark A. Bullock with the Southwest Research Institute. He'd find that easier to believe than the notion that humanoids could evolve independently elsewhere. Plus "it's been shown that panspermia is quite a viable mechanism, so the interchange of genetic material between worlds is not out of the question."