Wow the previous replies really left the original question behind for a bit huh. lol
The original question seems to be what are the odds that intelligent life elsewhere in the universe is likely to develop to a level that the SETI project might be able to find them.
First there’s been some discussion about what we mean by intelligence. Certainly there can be an argument made that most creatures with an advanced brain have some level of intelligence. I think mostly the idea is creatures that might have similar type of cognitive intelligence to ourselves.
What we’re really interested in finding is sentient beings that have intellectual abilities such as logic, reasoning, analyzing, prioritizing, abstract thought, etc. that are somewhat similar to our own. Further we need them to have developed some type of technology that might be discovered by SETI. This really narrows the scope down a lot.
The odds of finding beings of similar type intelligence as ourselves might be greater if we actually had the ability to visit other planets. Even if there are beings like that, not all of them will develop any type of advanced technology. They could have the greatest culture and philosophy in the universe, but no desire to look outward from their own world. Since we don’t have the technology ourselves to visit other worlds then we also need those beings to not just develop some type of civilization, but to develop a technological civilization advanced enough for interstellar communication themselves. This is where the challenge becomes even greater because not only does the civilization need to have the technology, it needs to have developed at the right time period for whatever signals it might have sent to arive at are SETI dishes in our lifetime. Unfortunately that means the other civilization would have to have existed long, long ago and may no longer be extant.
In order to find other sentient species that have a sufficiently similar type of intelligence and exist at the same time as us then both their species and ours will need to have a much more advanced technological abilities than we do now in order to find each other and develop communication.
The odds of the existence of extraterrestrial life somewhere in the universe may seem extremely high. Those odds become much less favorable as we start talking about other intelligent life forms that might exist at the same time as us, and that are sufficiently advanced to allow some form of contact or communication. As much as we’d like to think we aren’t alone in the universe it’s still possible that intelligent species haven’t yet ever existed at the same time in the universe. It’s kind of like an intergalactic lotto game. Maybe we’ll get lucky.
Oh yeah… There’s also the added condition that we want the species to be one that we actually want to find, or who we’d want to find us. Whenever thinking about this topic it’s a good idea to keep in mind the 1950 short story “To Serve Man” by Damon Knight. ;)