What Will Aliens Really Look Like?

by Seth Shostak, Senior Astronomer, SETI Institute

posted: 16 July 2009

According to Genesis 1:27, "God created man in His own image."  OK, but what about all the other intelligent, cosmic inhabitants?  Well, Hollywood has taken care of that. It has created aliens in man's image.

It's hardly a major revelation to point out that most movie aliens bear a strong likeness to humans. Typically, they have well defined heads, and two of everything else of note: eyes, nostrils, arms and ambulating legs. They're strongly anthropomorphic, and if some of these hairless little louts moved into your neighborhood, you'd probably get around to inviting them to dinner.

Aliens that resemble us are convenient for storytelling, because you already know how to read their intentions. Their behavioral cues are familiar, and you can tell if their game plan is to be amorous or aggressive. (In most movies, these are their only options.)

But is there reason to think that actual aliens, from a star system a thousand light-years away, would be similar in appearance to the evolved apes that we now call Homo sapiens? Some scientists, such as Cambridge University paleontologist Simon Conway Morris, think there is.  After all, there's a phenomenon in nature known as convergent evolution. It's the tendency of evolutionary processes to find similar solutions to any given environmental challenge. For instance, if you're a predator whose existence depends on catching lunch day after day, you probably have two eyes with overlapping fields of view. Stereo vision is a real plus for pouncing on prey.

Similarly, for marine creatures that have a need for speed, the laws of hydrodynamics favor being long, thin, and oh-so-streamlined. Convergent evolution has ensured that barracudas are shaped like dolphins, even though the former are fish and the latter are mammals. Being built like a torpedo just works better.

This mechanism is often invoked by sci-fi writers as a convenient explanation for why so many of their alien protagonists resemble earthlings brushed with battery acid. (Even the language - "convergent evolution" - which is so ponderously Latinate, bespeaks academic merit and scientific plausibility.)

As a consequence, it's possible that a hominid shape is the best body plan for sentient beings on any world, and no doubt Tinseltown would be pleased to learn that its rubber-suit aliens are good approximations to the real thing. But I'll bet you dollars to Devil Dogs that any extraterrestrials we detect won't be muscular guys with deep voices and corrugated foreheads, or even big-eyed, hairless grays. And that's not because such creatures couldn't exist. Rather, it's because of the timescale for non-biological evolution.

Here's the deal: it's widely believed that aliens are out there. But proof requires the following: Either aliens need to visit Earth (don't start!) or we need to detect them with our telescopes - for example, in one of our SETI experiments. In either case, we're dealing with beings whose technological level is beyond ours. That should be obvious because, after all, we're not yet at the point where we can engage in interstellar travel. And as for getting in touch via signals, well we're not blasting continuous, powerful transmissions to lots and lots of other worlds. We don't have either the money or the equipment. Maybe someday.

In fact, no matter how we find them - in the backyard, on the radio, or through our telescopes - any detected aliens will be at least a century beyond us. More likely, a millennium or more.

OK. But if they're beyond our technical level, what can we say about their appearance? Well, using our own experience as a guide, consider a human development that seems likely to take place sometime in the 21st century: we'll invent machine intelligence. Some futurists figure this dismaying development will take place before 2050. Maybe it will take twice that long. It doesn't matter. By 2100, our descendants will note that this was the century in which we spawned our successors.

So here's the point: Since any aliens we detect are ahead of us, they've already done this; they've made the transition from biological to engineered intelligence, and left behind the quaint paradigm of spongy brains sloshing in salt water.

In other words, and despite what "The X-Files" would have you believe, the sort of humanoid, fleshy aliens that routinely populate fiction are very unlikely to be the type we will discover. Instead, they'll be machines.  Dollars to Devil Dogs.

All of which reminds me: the next time your neighbor claims that extraterrestrials have once again hauled him out of his bedroom for distasteful experiments, ask whether the abductor was a protoplasmic being with four limbs, or some sort of complex hardware.  I think I already know what the answer will be, and it's the wrong one.

Seth Shostak's latest book is "Confessions of an Alien Hunter"