A Skeptical Look at Aliens

OK, I'm feeling guilty: I'm off at The Amaz!ng Meeting enjoying myself, and totally neglecting the blog readers who aren't lucky enough to be here too. And since I've been getting lots of requests to put the full content of my talk online, I figured…yeah, sure, I can do that. So here you go, all of the slides and what I said about them, mostly, below the fold. Criticize and argue and do your usual.

TAM is a tough crowd for me: it's a meeting where the emphasis is always on the space sciences, especially this year with a theme that just crows about astronomy, and I'm a biologist. It doesn't matter that I study the most interesting and complicated phenomena in the universe, Phil Plait is going to come along and start bragging about his giant hot balls of flaming gas that are ooooh so far far away, and everyone will be superficially impressed with how very big it is, and ignore how clever and intricate and amazing my subject of study is.

So I thought...aliens. Even astronomers are interested in that subject, and they get it all so wrong, so this might catch the attention of physicist-leaning attendees. And then I saw this news story on the wires, and saw an opportunity to also make fun of those naive astronomers.

OK, I'll grant that astronomers might have the data to make estimates of the frequency of planets in habitable zones around stars, but this idea that they'd necessarily be humanoids like us is nonsense, and there are no rational grounds for guessing that. But then, you know, I start pursuing this line of inquiry and realize I can't blame the attitude on a few fringe astronomers — it's pervasive in our culture with media that constantly portrays fictional aliens as looking almost exactly like us, either taller and bluer, or sometimes with latex appliances glued to their heads. Although this last picture suggests that there may be deeper differences in the anatomy of the perineum, since he's apparently flashing her the vulcan version of the shocker.

And then there are serious, renowned paleontologists like Simon Conway Morris, who wrote a whole book titled Life's Solution, in which he argued that the ultimate goal of evolution was intelligent humanoids who could understand God's word. His final chapter was a fantasy in purple prose in which a trio of aliens land on his lawn and walk up on two legs and look at him with two eyes and ask to come in for tea...so not only is evolution driving towards humans as life's solution, but they're going to be British.

And one more example: this is a display in the National Museum of Canada in Ottowa. That creature on the right is a reconstruction of a fossil Troodon; that was a real theropod that lived in the late Cretacous. It was relatively large brained, leading the creator to speculate...well, what if that meteor hadn't wiped out all the dinosaurs, giving Troodon the opportunity to evolve tool-using intelligence. Setting aside the obvious fact that Troodon was a successful beast as it was and there was not necessarily any evolutionary incentive to become more intelligent, the creator made that very silly mannequin on the left, suggesting that one perfectly serviceable saurian biped would abandon its functional form to look more like a scaly ape or a David Icke wet dream.

This is absurd for reasons I'll explain, but what it means is that I can't just pick on astronomers, and I had to throw out all my Phil Plait jokes, like pointing out the ubiquity of shiny hairless domes in these fantasies. Instead, I'll explain some evolutionary basics that apply here.

First, it isn't entirely crazy to argue for humanoids, and there's a perfectly good observed phenomenon that forms a rationale. It's called convergence. If you take organisms with initially similar body plans, and you put them in environments where there is selection for a particular function or a particular niche to fill, you'll sometimes see superficially similar solutions emerge. On the left is the Tasmanian Tiger or thylacine, a presumably extinct marsupial that filled the role of large predator; on the right is another large predator, the grey wolf. You should be able to see that independently, on different continents, local mammals evolved to be fast, active hunters with fanged jaws — and they do look somewhat similar. Of course, when you look in detail at the anatomy, the differences leap out at you, and no wolf or thylacine would confuse one for the other.

I would concede that if a primitive primate were to somehow colonize an alien world, and if that lineage gave rise to an intelligent tool-user, it would probably look vaguely humanoid, at least as much as the thylacine looks like a wolfoid. But here's the catch: with a different genetic stock, there are many different solutions to the same fundamental problem. Consider just the bipedalism part.

These are all bipeds. We're not going to confuse them for each other, not even in a dim room. Another factor behind the convergence here is that all of these are ancestrally related: they're all tetrapods, or derived from four-limbed ancestors. We're bipeds because we're limited to only four limbs, and if one pair gets specialized for a specific function, you're only left for two for locomotion. So this is a product of an ancestral limitation.

Look at other lineages with no such limiting heritage, and bipeds are really, really rare. Among the invertebrates, the closest thing I could find to that vertical posture is something like a praying mantis, but of course it's got four legs dedicated to movement. Bipedalism really is nothing more than an oddball vertebrate artifact. We can go further, too: all these creatures have heads with faces with two eyes and jaws and a nose...that's not a necessary arrangement. Just look at arthropod faces.

See? If this guy lands in your front lawn and asks for a cup of tea, you aren't going to confuse him with Richard Wiseman. And it's not just superficial differences in appearance, it's about deep functional differences. Let me give you one example of very different solutions to a common problem, how to eat in an aquatic environment. The thing is, if you rush forward through a dense medium like water, you're also pushing a mass of water in front of you that will actually push your prey away from you. So let's think about how to catch that tasty food item in front of you.

Bony fish have a brilliant solution. They have toothy jaws and what they have is a regular cranial ballet of adaptations that allow them to capture prey. When they lunge forward, the jaw gapes and the gill covers flare, greatly expanding the volume of the oral cavity — so as they advance, they also suck in a huge volume of water, swallowing the mass of water in front of them and hopefully also the prey within it. It's very cool. Some fish go even further with extreme adaptations, like this moray eel that also has a second set of jaws slung deep in its throat. So it lunges, opens wide like a typical fish, and then also spears the prey with the little jaws, which clamp down and hold it in place while the big jaws tear it to shreds. Awesome, right? You may have seen something similar in a science fiction movie.

But is this the only way to solve the hydrodynamic problem? No, of course not. Let's look at squid.

These are frames from a high speed cinematographic record of a squid catching a shrimp, with each frame separated by 10 milliseconds. So this whole movie covers only about an eigth of a second. The squid starts with all 10 arms pressed tightly to one another, forming a streamlined cone; then the central two tentacles spear outwards to grasp the shrimp, while the other eight flare outwards and fling backwards to counterbalance it. And then, dinner. It's beautiful. It's the same physical problem for both fish and squid — fast prey capture in a dense medium — but radically different biological solutions.

Why do they differ so much? One reason is history.

Different phyla of organisms have different ancestral roots which constrains available solutions. On the top is an inferred Pre-Cambrian chordate: it has a dorsal nerve cord, a central springy skeleton called the notochord, and a post-anal tail for swimming. This is an animal specialized for swimming, and it has no limbs; limbs evolved later and are a kind of last minute change bolted on — vertebrates have always suffered from a dearth of limbs, hence bipedalism.
At the bottom is an arthropod. Key elements of their body plan is an inversion of central organs — a ventral nerve cord instead of a dorsal one — and a set of limbs on every segment. Arthropods have had limbs to spare.

This top picture is our heritage: it affects everything evolution can do to modify its descendants. It's easy to see how some forms are dependent on that.

This is one of the pinnacles of vertebrate evolution, a bony fish. There are over 30,000 species of fish, so hands-down, this is the most successful vertebrate solution ever. Note the streamlined form, the torpedo shape; its internal skeleton is a flexible spring, that notochord modified, flanked by big slabs of muscle that propel it through the water. At the front end is a sensory array, eyes and pressure and olfactory sensors, and elaborate jaws and prey-capture reflexes that I've already mentioned. This is the perfect product of adaptive function; surely every planet we visit someday will have to have fishoids, torpedo-shaped predators, right?

Hang on, wait: here's the perfect product of adaptive evolution. Physics dictates that torpedo shape, but there are many arrangements of body parts that can produce that. Here, the sensory array is midbody; the front is dominated by manipulatory appendages. There is no internal skeleton. Movement is acheived by flying through the water with these fins, or by contractions of his muscular tube to generate jet propulsion.

So fishoids aren't necessarily interplanetary universals. Let's not go the other way and suggest that squidoids are, either — the answer is that nature is always going to surprise us with novel solutions, and working backwards to make a Panglossian rationalization that every solution represents the best of all possible solutions is a fallacy.

So why do squid look so different from fish? It's the body plan.

This is the squid body plan, revealed in embryos of the three extant divisions of the group. They're all a visceral bag with muscular appendages dangling down. That's the root stock evolution has to work with.

It's the pinewood derby problem. All former cub scouts remember this: you're handed a rectangular block of wood, 4 plastic wheels, and some miscellaneous fasteners, and you're told to shape this into a model vehicle to race down a runway. Everyone comes up with similar solutions, but the details can be creative and inventive.

But what if, instead, the cub scouts were handed a big lump of putty, some ball bearings, and a dozen balloons, and told to make a racer? What if it were a bucket of plastic straws, some plaster of paris, and a gerbil? Different starting conditions, very different solutions will emerge.

I have to say a few words about intelligence. And that is, intelligence doesn't seem to be a very likely solution to evolutionary problems — it's like a wacky pinewood derby car made by balancing the block of wood on end and turning it into a unicycle. Maybe there's a design that would work, but it seems to be rather improbable. And Nature has had opportunities to try.

This is a diagram of the history of earth from a biological perspective. What it illustrates that life thrives for long periods of 10s to 100s of millions of years, and then 5 times in the past half-billion years, there have been abrupt mass extinctions: geologically short intervals in which 90-99% of all of the animal species on the planet have been totally wiped out, followed by regrowth and expansion. The best known is the Cretaceous extinction, 65 mya, which exterminated the dinosaurs. The biggest was the Permian extinction, 250 million years ago, that simply devastated the planet. Each of these was like a big game-over moment, a reset that wiped the slate mostly clean, and then resumed play. So we can think of this as 6 related but alien worlds, 6 trials to see if evolution would spit up an intelligent tool-using species. Now to be fair, let's exclude the first two; animal life was primarily aquatic, so maybe its fair to say they don't have a chance to invent fire: but these later four all had large, complex, terrestrial animals in complex environments. And only now in the quaternary has it happened.

Even there, once tool-using intelligence emerges, it can expand rather quickly. We hominids evolved like lightning, over a few million years; yet Troodon didn't do it, no other terrestrial animals have done it quite like we have at any time in the last 400 million years.

Intelligence is not a ubiquitous adaptation. It's not like fangs or claws or wings or eyes, features that pop up independently in multiple lineages. It's a great rarity. And we can't even judge whether, on a geological scale, it's even a long-term evolutionary success — we've had agriculture for only a few thousand years, industrial technologies for only a few hundred, and we can already see major obstacles to our survival looming on the horizon.

Maybe we should also recognize that intelligence doesn't seem to be one kind of thing, either.

Here are representatives of four groups of animals that show great potential for intelligence: they're self-aware, puzzle-solving, curious and exploring creatures: the primates, some birds like the Steller's Jays shown here, cetaceans, and octopods. Science fiction stories love to speculate about meeting and communicating with aliens, but they always cheat and make the aliens mirrors of ourselves, so it's relatively easy. Here are four species that are far more closely related to us, that share far more in common with us, than any aliens we might ever encounter. Yet we're trying harder to listen to the conversations of unknown aliens with SETI than we are trying to have a chat with our next door neighbor, Octopus vulgaris. I suggest to you that extraterrestrial aliens are not impossible, but they may be rarer than you think, and furthermore, that they're going to be weirder than you can imagine. And if you can't think of what to say to an earthbound intelligent mollusc, you're going to have a really tough time with the biochemically bizarre, anatomically improbable, historically unrelated tentacled blobs of Fomalhaut or whatever.

To summarize:

These are some general principles of biology that will universally apply. Evolution doesn't just make finely tuned functional organisms, but is also built on a foundation of chance, so it spawns endless diversity. Every advance carries along the baggage of its ancestry, so we see echoes of our past in every feature. And the more specific and complex a feature is, and intelligence is both of those, the less likely it is to emerge in the same form in different lineages.

And then there was a little bit that I had to leave off the talk.