The existence of Intelligent Extraterrestrial life is a common topic for Science fiction - stories, movies or even discussions. There are various visions of an alien proposed - doomsday / apocalypse themed movies portray them as reptiles with high frequency reproduction capabilities. However, few other more benevolent themes like the E.T. or Avatar show them as humanoid. Which of these two versions are more likely to be true?
- The use of tools
- The ability to learn and remember (obtain knowledge) through experience, study, or instruction
- The ability to communicate (the ability to give and receive information)
- The ability to solve complex problems
Next is our ability to learn from instruction which takes us to our eyes, ears and mouth - eyes and ears allow us to receive instruction while the mouth helps in giving instruction. Again, cognitive development plays its own role in interpretation of what the eyes see or ears hear.
Next is our ability to communicate - as earlier we communicate using sounds from our mouth (and receive through ears), but one often unappreciated difference between human and animal communication is our ability to form facial expressions. While other animals also emote expressions from faces, none is as versatile as humans. We can communicate through eyes or certain facial muscles as well.
And finally, the last thing which differentiates mankind from other animals is our ability to think and solve complex problems. Our brain is a powerhouse of not only cognitive intelligence which makes our other 'sensory organs' effective, but also analytical intelligence which is responsible for everything from language to say our ability to build rockets that go into outer space!
Any intelligent animal or say an alien - if intelligent will most probably have to be equal to humans in all the above capabilities and it follows that they will need eyes, ears, mouth, fingers and a significantly large brain! So aliens shaped like cows or goat or sheep or giant lizard or dinosaurs may not be practical. Any advanced life form will mostly evolve into humanoid shapes to able able to carry out complex tasks. In fact, not only will aliens be humanoid, they will actually be Carbon based or at best Silicon based given that Carbon and Silicon are most abundant elements in the Universe!
One caveat here is that we are only talking about intelligent animals capable of being at least as intelligent as a chimpanzee or more. So a Godzilla like alien is still possible, provided we do not call it an 'intelligent animal'! However, most extraterrestrial themed movies show the alien civilizations contacting humans by flying to earth in a spaceship which presumes they are intelligent animals.
To cap the subject, it isn't really necessary that, if there is life elsewhere in the Universe, it is intelligent. Here's an interesting debate between Niel De'grass Tyson and Richard Dawkins on the same subject.
**Image Credit: 'Dobbie the Extra-Terrestrial' on Flickr