Michigan

I got a question. Taking into account what we know about life, do you think that creatures on another planet would have to exhibit lateral symmetry? It is always the case in the movies, I always wondered if it was by lack of imagination or because they know something I don't. And what about the back/front asymmetry which is similar for all creatures I know? Thanks (when you have a minute, I would appreciate this).

Well, sponges on earth exhibit no particular symmetry, and neither do Placozoa. Cnidaria (jellyfish, hydras, etc.) and echinoderms (starfish, sea urchins, etc.) have radial symmetry, not lateral symmetry. It's not hard to envision that different sorts of symmetries could have been dominant on earth.

Movie monsters/aliens were historically limited to shapes that could be manipulated by a human, which tended to mean bilateral symmetry. With CGI, movies are limited more by the filmmaker's imagination, and what the studio thinks an audience will accept. Hopefully we'll see more movies with radially symmetric aliens, or other sorts of odd symmetries

Well, there always is "The Blob," a 1958 film starring then-unknown actor Steve McQueen. The New York Times movie critic described the "creature" as:

"...a quivering, gelatinous organism, left by a shooting star. It slithers around a small town, swollen enormously by various gobbled citizens, and finally holds the town at bay. They ultimately freeze it and transport it to the Arctic, where it is dropped in a parachute".

While I'm not a biologist, I've read fairly convincing arguments that symmetry is likely to be a common development simply because it reduces the number of instructions needed to build things. A take "these blueprints, flip them around and copy them" type of arrangement is likely to be easier to encode and more robust against errors. (At least any errors which are duplicated multiple times will likely greatly reduce survivability and thus are selected against.)

That being said, bilateral symmetry would seem to be the simplist of any symmetry. I've read a few arguments for bilateral symmetry as likely being most common universally. However, I've found those arguments unconvincing and lacking in real data. As Josh says, there are examples of organisms with different symmetries even on earth, how can we claim that they are not common elsewhere in the universe?

Why, there could be a creature with up-down bilateral symmetry as well as hexagonal radial symmetry swimming in some soup in another planet someplace making the claim to its comrade that bi-hexagonal symmetry is the only logical form of life.

P.S. Thanks for comming to Michigan, Josh. We dusted, but it was with snow.