Have you all read about the discovery of a potentially Earthlike, life-bearing planet orbiting a distant red dwarf star? That's an encouraging step toward the refutation of the pessimistic view that the reason the aliens haven't contacted us is that there aren't any—that life as we know it is so rare throughout the cosmos that it's statistically unlikely for any advanced extraterrestrial civilization to spring up during the lifespan of our species. Recent discoveries have refreshingly suggested that planets are a not uncommon feature of the life cycles of stars. Now we have concrete reason to hope that Earthlike planets aren't uncommon, either.
How likely, however, is it that their inhabitants, even if intelligent, will resemble us? Some xenobiologists maintain that the humanoid shape, bipedal with manipulative limbs free to handle objects and with a head at the top to house the brain and sensory organs, is a logical body design likely to be replicated many times over on a multitude of planets. That view might be cast in doubt, though, by the reminder that right here on our own planet, lots of creatures who share our favored habitat don't look anything like us. Cats, dogs, spiders, roaches, and ants, for example, live quite contentedly in our houses. And I see no intrinsic reason why, given a nudge in a different direction, evolution couldn't have produced sapient felids or canids rather than sapient primates. Nor would they necessarily have to become bipeds. In Heinlein's delightful novel STAR BEAST, it's assumed that Lummox, the hero's eight-legged alien pet, can't be kin to an intelligent species that otherwise resembles her because she doesn't have hands. Well, surprise, she develops manipulative forelimbs with maturity. What about non-mammals? On land, crustaceans, cephalopods, and arthropods (insects, spiders, etc.) seem poor candidates for brains large enough to harbor intelligence. In water, however, such species don't have size limitations. Sapient giant squids or crabs look perfectly feasible in an aquatic environment. The Creator (or the creative process working through evolution, depending upon your viewpoint) is capable of almost infinite variety. So should we expect a STAR TREK universe inhabited by dozens of alien races who look almost like us except for cosmetic variations? Or should we prepare for extraterrestrial neighbors in a myriad of forms we can only begin to imagine?
As a writer of spec fic romance, I of course opt for the former, because I want aliens my human characters can plausibly fall in love with. In paranormal romances, for example, I'm perfectly willing to suspend disbelief in extraterrestrial vampires who can pass for human. But in the primary-world cosmos, I suspect the latter will prove more likely.