I found this pretty interesting, both as a biologist and a science-fiction writer. Excerpt:
On the website for the department of zoology of the University of Cambridge, the page for Arik Kershenbaum lists his three main areas of research, one of which stands out from the others. Kershenbaum studies “Wolves & other canids,” “Dolphins & cetaceans” — and “Aliens.” Granted, science hasn’t yet found any aliens to study, but Kershenbaum says that there are certain things we can still say about them with reasonable certainty. Topping the list: They evolved.
“The bottom line — why animals do the things that they do, why they are the things that they are — is because of evolution,” said Kershenbaum, a lecturer and director of studies in the natural sciences at the university’s Girton College. He argues that evolution is a universal law of nature, like gravity — and that studies of plants and animals here can therefore tell us something useful about potential inhabitants of worlds far beyond Earth. He finds evidence for this in the process of evolutionary convergence, in which unrelated lineages of organisms evolve similar features as adaptations to similar environmental challenges. It’s an argument he presents in detail in his new book, The Zoologist’s Guide to the Galaxy: What Animals on Earth Reveal About Aliens — and Ourselves, which draws on comparisons of animals’ physical adaptations as well as his own research (and that of others) into animal communications.
In science-fiction, it’s common (I’m guilty of it myself) to portray intelligent aliens as just humans with funny features, and that’s more an artifact of story-telling than it is science, as your characters have to have a degree of similarity enough to make social interaction possible. But it’s far more likely that even intelligent aliens would be truly alien, to the point at which we probably wouldn’t even be able to communicate with them in any meaningful way.
But how different would they be, in the broad strokes?
Well, look at life here on Earth. Thanks to a set of genetic instructions called hox genes, most multi-celled life is organized fore-and-aft, with a mouth at one end and an anus at the other. Sensory apparatuses are at the fore-end, near the mouth, because their original purpose was to detect food. The central nervous processing center, that would eventually become a brain, would usually develop near those sensory inputs, the better to reduce reaction times. And as organisms become more complex, they would have to have some kind of ways to move, and then, later, to manipulate their environment – limbs.
So a creature with a head with the senses on the head, a body, and some number of limbs, would seem to be a sort of biological default. And to evolve into a technological society, they would have to have not only the intelligence but the ability to use and make tools, so either hands or some approximation of same.
Now, there’s no requirement for bilateral symmetry or even a tetrapodal layout; you could have an intelligent, technological race that uses flashing lights rather than sound for communication, is organized in a trilateral rather than bilateral body plan, and is a hexapod rather than a tetrapod.
You know – alien.
I think I’ll grab a copy of Dr. Kershenbaum’s book. It looks to be an interesting read.