One of the most irritating aspects of popular science fiction in movies and television is that the aliens almost always end up looking pretty much like us. There are valid reasons for that on screen – it’s a lot cheaper to mess around with some facial makeup than to develop entire CGI species (and plenty of classic TV series, like Star Trek, precede modern CGI by years). What about in real life, though? Would aliens look like us?
It’s tough to answer this question confidently because we just don’t have enough evidence to work with. There are about a hundred billion stars in our galaxy, and probably a hundred billion galaxies (or more) in the universe – but we only have one intelligent species, ourselves, as a working model of an intelligent species. We can make a few educated guesses, however.
First, the obvious: human beings are the product of hundreds of millions of years of evolution. The farther back you go on the evolutionary tree, the more generic our ancestors become, but the most important advances – things like bipedalism and a very large brain – came only very recently. It would be a mistake to assume that another intelligent species, evolving on an alien world from alien ancestors, would have two arms, two legs, a bipedal structure, two eyes, and so on and so forth. Even looking around on Earth, there are at least four largely unrelated groups of animals that could be said to have at least some rudimentary form of advanced intelligence: intelligent cephalopods (certain types of octopi and squids), social insects (like ants and honeybees), dolphins and other cetaceans, and primates, especially humans. Dolphins and humans are mammals, and all but the cephalopods are vertebrates (meaning they have backbones), but the amount of diversity that can develop just on Earth gives us reason to believe that intelligent species on an alien planet would not look anything like us.
On the other hand, there is a competing factor which works in favour of aliens looking like us: when certain features provide a survival advantage, they can arise independently and even look similar, despite being actually unrelated. This is known as convergent evolution. It remains to be seen whether advanced intelligence is actually a survival advantage, but we can see the process of convergent evolution elsewhere. For instance, bats, birds, and pterosaurs all evolved the capacity for flight independently – through tools like winged arms, and hollow bones. It may be that intelligence is part of a process that led to humans, which also involved bipedalism, opposable thumbs leading to tool use, and so on. If there are certain biological features which allowed us to get an edge over our prehistoric rivals, it’s not impossible to believe that an alien species might have gained a similar advantage through similar features.
On the whole, the question can’t be answered until we actually find an intelligent alien species, so that we can make an intelligent comparison. Probably, however, aliens won’t look like us – and, unlike on television, they certainly won’t speak English.
