Posted 06 December 2012 - 05:41 PM
I've been thinking about this lately. I think we have to look at the circumstances of the evolution of intelligent humans here on Earth. First, we have the right environment. Secondly, we have a large moon that stabilizes the rotation of our planet. But thirdly, the evolution from primate to human was a lucky accident of the extinction of the dinosaurs and local geology and environment.
Also, what kind of life will evolve into intelligent creatures? I think it is no accident that primates evolved intelligence. They are very mobile, they have four useful appendages, they have the ability to walk upright and they have hands and fingers, and they're pretty smart to begin with.
I don't think any other type of species could evolve into intelligent creatures such as us. I don't think cows, for example, will ever become more intelligent than they already are. They don't need to. Predators have a better chance, but if you are a successful predator, you don't need to evolve, either. Only one kind of animal (monkeys) have this evolutionary opportunity, and for them it takes a very selective and exceptional environmental challenge for the opportunity to arise for them to evolve into a human-level intelligence.
Given these unique circumstances here on Earth, I don't think there are many planets in our galaxy that support intelligent life equal to we humans. I think intelligent life is very rare in the galaxy, and given the great distances between stars and the difficulty this presents for mutual communication, we may never discover another intelligent species we can communicate with.