Notes on Worldbuilding, Part 17: Aliens!

We've finally arrived at discussing actual intelligent extraterrestrial beings. I'm going to come at this concept from two directions in separate posts. This entry will discuss the science of alien beings — what they might be like, based on all the previous worldbuilding entries in this series. My next entry will look at aliens from a literary perspective, discussing what roles they can play in a story.

I can't list all the possible forms alien life may take. Look at the amazing variety of life on Earth, then realize that alien life will likely be even more diverse and strange. However, we can draw some basic ideas from biology and physics.

Size: The size range for intelligent beings is pretty big. What's the smallest brain capable of intelligence? How much does the brain-to-body ratio matter? How much does the structure of a brain matter? We're only just beginning to find out.

I think a human infant's brain is definitely big enough for intelligence (especially since we have seen very small adult humans with no sign of any impairment). Smaller than that we have only animals to guide us, and we have to figure out whether size or structure of a brain is more important for intelligence. Certainly some birds — ravens, crows, parrots — are disturbingly intelligent, with brains massing only 10-20 grams (while a human brain can be a hundred times bigger).

Let's call that the low end. We can also assume that a brain-to-body ratio of 1:20 (twice the proportions of a human brain) is the maximum possible, simply because brains are such energy hogs that an organism couldn't eat fast enough to support one any bigger. That gives us a minimum size for an intelligent being of 200 grams. That's the size of a large bird or a small monkey. With a more efficient brain organization, I can believe a creature like that would be capable of human-level intelligence.

At the upper end . . . well, that's a darn good question. Sperm whale brains are nearly 8 kilograms, and whales are famously intelligent animals. It's very easy to imagine whales with human-level intelligence — indeed, some people think they are as intelligent as humans. So I'm going to say there is no upper bound to how big an intelligent being can be, subject to the limits of physics.

Which we will now address. The largest land animals on Earth were the sauropod dinosaurs, some of which weighed in at close to 100 tons. On other worlds that would scale more or less with surface gravity. The square-cub law starts to bite hard when you get an organism of that size.

On land, that is. At sea, I don't think there is a limit to size, other than food supply. On an ocean world you could have marine grazers miles long, and some immense species might evolve intelligence, presumably via the route of language, social manipulation, and herding prey. If they were whale-like, it's hard to imagine they could develop much technology, but among the invertebrates there are plenty of marine animals with superb manipulating appendages.

Senses: Everybody knows that humans have five senses — seeing, hearing, smelling, tasting, and touching. Except that we actually have at least eight, since we can also sense temperature, feel the position and motions of our own bodies (proprioception), and detect gravity and acceleration (balance). But even on Earth there are other senses used by living things. Electric field sense, magnetic field sense, directional heat sense, and echolocation.

As near as I can tell, senses come in three main categories. Electromagnetic sense (vision, directional heat sense, and electric and magnetic fields); Physical sense (sound, infrasound, ultrasound, proprioception, touch, body temperature, balance, and echolocation); and Molecule detection (smell and taste). Because I have no patience for woo, we will ignore "psionic" senses.

Alien beings might add more senses in those categories. One can imagine alien beings using radio wave detection, radar, x-ray sensing, infrasonic or ultrasonic hearing, or maybe scent gradients to perceive the world around them.

It seems likely that sense organs will be located near the brain, and in most animals that would be near the front or top of the organism. Front because that's the way you move, and senses keep you from bumping into things or falling off cliffs. Top because it gives you more range. Chemical senses might concentrate near an organism's mouth (or other feeding organ) to detect whether things are good to eat.

Limbs: Humans have two arms and two legs, and most land vertebrates have the same four-limb arrangement. But that's mostly a historical accident: the first fish which adapted to life on land had four fins. They might just as well have had six, or eight. Invertebrates can have dozens. I strongly suspect that any alien organisms we encounter (or, more likely, exchange radio transmissions with) will have more limbs than we do. If you're building aliens, you can pick whatever number you like. Remember that in addition to limbs, there are also trunks, prehensile tails, prehensile mouthparts, tentacles, and tongues. One can imagine beings creating a technological civilization using any or all of them.

Skin: Life on Earth has a huge variety of outer coverings. Snails rely on a coating of mucus to protect their very thin skins. Humans have bare skin suitable for a hot climate. Birds have superb insulating feathers. Mammals have fur, almost as good. Fish have scales, reptiles have different scales, a few animals have armor plating — and that's not even considering all the ways plants garb themselves for protection. There's no reason alien beings can't have skin like tree bark or cactus rind.

An organism's outer covering protects against whatever the biggest local threats are — sunlight, cold, predators, parasites, dryness, and so on. Alien hides will likely be much the same.

Many organisms on Earth use their skins as billboards. Octopuses express some fairly complex emotions by changing the color of their skin. Other organisms shift color for camouflage, or to aid in temperature control.

Minds: This is the big one. This is really the only reason to go through the whole process of designing a planet, designing life, and designing intelligence. The whole process is aimed at producing an alien mind. A mind which does not think the way humans do. Otherwise, why not just write about humans? Alien minds are such an important topic that I'm going to put this one aside for my next post.

Comments

[William H. Stoddard]

The issue for brain size may not be, or not be only, absolute mass. It appears that mammal brains, at least, tend to have a mass that's proportional to body surface area. That kind of makes sense, if you figure that a substantial part of the neocortex is elaborate maps of the body surface, which accounts for two dimensions of brain volume, and that cortical columns in all mammals have more or less the same thickness, which accounts for a third dimension. So brain mass ought to go as somewhere around the 2/3 or 3/4 power of body mass. If you divide human body mass by 100, you might divide human brain mass by around 30, going to somewhere around 40 ml, I think.

Now, human brains are huge in proportion to body surface area. Other hominids such as chimpanzees have only about half as much; other primates, and I believe songbirds, have half as much as THAT; and generic mammals have half as much as that---at least according to the book I keep on my shelves, though its results aren't recent.

I suppose there could also be a requirement for absolute brain mass to support some more complex cognitive functions. I haven't seen any studies of that issue.

[Jim Cambias]

That's a really interesting idea I had not encountered. Most discussions of "cephalization" stick to brain vs. body mass -- presumably because it's easier than figuring out surface area.

I wonder if whales and elephants get an IQ boost by virtue of having thick hide -- their large surface area is relatively under-supplied with sensory nerves thereby giving them an effectively higher brain to body surface area ratio.

Thanks for the info!

[William H. Stoddard]

Some of that applies to humans as well. If you look at homunculus diagrams (showing which parts of the cortex represent tactile and motor neurons for which parts of the body), you'll see that the human hands are enormous, taking up as much space as the rest of the body below the neck, and the same is true of the human face (with the tongue having a disproportionate share). Tactile neurons on your legs and your back are pretty far apart. Of course, a huge share of our sapience involves things we do with our hands and our speech organs.

I once saw a homunculus for a platypus, and it had huge overrepresentation for the bill, where the electrosensory organs are located. And I expect that an elephant's brain map would have a huge trunk.