Alien aliens (let's get physical)

Easy things first ... how should aliens look?

Well, most likely alien. Even (as in this post) aliens who evolved on Earthlike planets.

That's not to say they shouldn't ever share some anatomical features with terrestrial life. What works on Earth remains our only data point for what can work. That said, even terrestrial life shows more variety than some SF aliens.

Take bilateral symmetry with four limbs. Yes, many earthly animals follow that design. For most of us, left/right symmetry and four limbs were inherited from very primitive ancestors. Had we descended from starfish or octopi -- and given a different timing of inopportune asteroid strikes, that might have happened -- we would look a lot different.

Adding or removing a limb is an improvement on the Lerner alien-o-meter scale. The Puppeteers of Larry Niven's Known Space have three legs and two necks/arms. They remain left/right symmetric. The third/rear leg is markedly different from the front two, leading to distinct front and back. So in that way, not entirely alien ...

(Full disclosure: I co-write about Puppeteers, and I feel I've made contributions to their sociology. Their physiology was defined before I came onto the scene.)

Let's go further, with some symmetry breaking. My 2005 novel Moonstruck involves aliens called the Krulirim. A Krul's three limbs serve as arms and legs. It has three sensory clusters, also equally spaced. Picture a Weber kettle BBQ grill (the charcoal kind, for those of us who like to make fire) with hands -- though not quite like human hands -- at the end of its tripod legs.

A Krul has no notion of left or right, of front or back. Its worldview is radially symmetric. Unless a Krul is asleep, you can't sneak up on it. Nothing nearby is out of its sight. You or I might refer to an object by its distance to one side or another, and the distance in front or behind us -- basically, Cartesian coordinates, centered on our own body. That doesn't work for a Krul. So a Krul locates objects via polar coordinates: the distance from the body and the angle from a reference point.

"Aha!" you say. If a Krul is radially symmetric, how does it define that reference point? It needs an out-of-body reference point, so I gave Krulirim a magnetic sense. The reference for angular measurements is the bearing on the magnetic pole. (Terrestrial birds navigate magnetically. Why not Krulirim?) Two Krulirim comparing notes on the location of an object have to do trig in their minds.

This body plan made the aliens have an unfamiliar-to-us worldview and required a sensory mode only weakly present, if at all, in most terrestrial life. These bodily features wound up driving some plot points (I'll omit spoilers, in case I've made anyone curious). The Krul body design also gave me a real workout, trying to eradicate every reference to front, back, and sides that crept into the narrative because they're endemic to our language.

So, Guideline One: Alien aliens look alien.