[chris (OP)]

Peter asks:

It took billion of years for life on earth to evolve humans. Is it conceivable that a different form of life that is just as intelligent – and civilization building in some roughly comparable way – would evolve in the future, or would have evolved (now undetectably) in the past?

What do you think?

[Kryptid]

Given enough time, it's possible. The general trend for the evolution of life on Earth is that the intelligence of the smartest species alive at the time becomes greater over time. At the beginning, there were only single-celled organisms. Then came colonial animals like sponges, which were more complicated than microbes, but still had no brains. Then came simple worm-like creatures with the bare beginnings of brains. Eventually, those became fish with moderately-developed brains. Fish evolved into amphibians, and those into reptiles. I'm pretty sure that at least some reptiles, like Nile monitors, are smarter than most fish. Intelligence really started taking off with the evolution of mammals and birds (and possibly some non-avian dinosaurs as well, like Troodon). Parrots and ravens have impressive intelligence, as do elephants, dolphins and apes. Then, as you know, those apes became humans and their immediate ancestors.

That doesn't necessarily mean that more intelligent forms will evolve in the future. We have only about 800 million years left before a mass extinction induced by the expanding Sun will prevent such a thing from occurring. However, it's certainly possible that other apes could evolve into something as smart as modern humans if we were to get out of their way and open up ecological niches for them. It only took 6-10 million years for something with chimp-like intelligence to evolve into us. So the best chance would be given to species which are already pretty smart. If some of the smarter theropod dinosaurs had survived the K-Pg extinction event, perhaps even they could have become something technological as well.

[evan_au]

At this stage we can't communicate with apes, dolphins, whales, elephants, crows and octopi, so we really don't know how intelligent they are.
We can do simple tests that show that in some ways they perform as well as human children.

Human technological development is a fairly recent development, while there are suggestions from skull size that dolphins, whales & elephants may have had their current level of intelligence for much longer.

One of the questions raised by SETI is: Could technology be ultimately self-destructive? Will humans develop technology to the point where we destroy the Earth's ecology (and ourselves)?

Would living more harmoniously with the environment (like some of the other species mentioned above) be ultimately more successful, on a timescale of millions of years?

Of course, you need a space travel capability to outrun an expanding Sun on a timescale of a billion years or so, so there are limits to living harmoniously with Earth's environment...

[SymeAaro]

Intelligent life can exist in many forms. However, intelligence is based on the animal surroundings. For example, a dolphin has to be intelligent to work together to heard fish. However, a snake is not so intelligent, it strikes and eats and reproduces as a result of instinct, and there is no need for intelligence. So it depends on the conditions. Some people say humans evolved to compete with other homo species, or simply to gain an upper hand in order to hunt the mega fauna that existed at the time. Given the right situation, intelligence could evolve, but it depends on how evolution acts.
An interesting proposal was raised by Arthur C. Clarke in his book "2001" and the sequels - that intelligent life, from elsewhere in the universe, experimented on simple animals, to encourage the development of intelligence. So perhaps we are the result of another race. But this is highly unlikely.

[Monox D. I-Fly]

(and possibly some non-avian dinosaurs as well, like Troodon).

Which dinosaur is Troodon? Never heard of that one.