It must be said that there may be salient scientific logic behind an artistic adherence to a terrestrial lexicon in calculating the physical appearance of the extraterrestrial. If carbon, oxygen, nitrogen, hydrogen, often called the chemical “building blocks of life” (and by extension, the physical forces exerted upon planetary life —temperature, gravity, radiation, etc.) are universal —not specific to Earth alone, then by extrapolation life on other planets will probably also inevitably bear resemblance to our terrestrial life forms. Terrestrial life forms —however divergent —evolve with similar basic requirements: eating, reproducing, locomotion, etc. These universal needs give way to features and appendages for all known earthly creatures that, while divergent in appearance, are analogous in function. Would an extraterrestrial creature be constrained by these same basic needs, and would its shape and form reflect such constraints? Many scientists believe so. Writes Astrobiology Center at Columbia University director Caleb Scharf,
Not to say that life can always manage to evolve to a complex level, but if the window of opportunity is large enough, it will . . . Life like us (that is, complex-celled, dexterous, cerebral, linguistic, and technological) was going to happen given the slightest chance.