In my opinion, evolution on our own planet is a great model for what we would expect for life elsewhere. More specifically, convergent evolution holds the evidence we need.
For example, eyes evolved independently in several different lineages. We would also expect life on other planets to have eyes. Wings also evolved in several different lineages, from insects to huge flying reptiles. It doesn't matter if you have 6 legs and an exoskeleton or 4 legs and an internal skeleton, wings are advantageous, as are eyes.
At the same time, these features require a nervous system, a way of coordinating sensory input and the firing of the musclature, at least for multicelluar organisms (there are single celled organisms with "eyes"). We can also see that intelligence has also evolved independently in several lineages. A great example is cephalopods. The ancestor of molluscs probably did not have a complex set of ganglia, or anything approaching what you would consider intelligentce. However, cuttlefish are relatively intelligent predators that communicate with each other through a language of colors expressed by their chromatophores. They have a rather well developed central ganglia and nervous system. The only thing really holding them back is the lack of myelin sheaths around their axons.
So why did our lineage, including our ape cousins and even our more distantly related primate cousins, become so intelligent? I think it comes down to our ability to use tools, to manipulate the environment around us. Other lineages lack this ability. Cetaceans can not grab rocks and use them to bang open molluscs that they would otherwise not be able to get to. Having hands makes all of the difference, IMHO. Without hands any further increase in intelligence can not be used.
If an ape level of intelligence were to evolve on another planet I believe that this lineage would need something like our hands. Hands allow us to develop technologies. An increase in intelligence allowing us to communicate these technologies to further generations will also be selected for. Even in chimp groups we see one generation teaching tool use to the next generation. What we see in such lineages is a selection of learned behavior instead of instinctual behavior. This is also a very important step, IMHO.
On a more philosophical note, we still don't know if a human level of intelligence is a good adaptation in the long run. We have built technology that is capable of wiping out our entire species. For all we know, this type of evolved intelligence is a dead end. Perhaps it self desctructs more often thant it doesn't. Human like intelligence may be a candle that burns very bright for a very brief time on the scale of evolutionary time lines. What we may find on other planets is archaeological evidence for cultures that reached our level of technology and then disappeared soon afterwards.
Or maybey everything will work out just fine and we will all have flying cars within the next decade!!! I NEED FLYING CARS!! WHY CAN'T THEY GIVE ME FLYING CARS!!! hehehe
But wings I'd say require a little more than just the Sun.
Indeed. I was thinking about this a little bit more, and there are other parameters. First, you need a planet about the size of ours. If gravity is too high then flying is just too ineffecient. If the planet is too small then it eventually cools, loses its magnetic field, and then loses its atmosphere. This is what happened to Mars.
With land and the right amount of gravity I think we can safely assume that flight will evolve since it evolved several times in the evolution of life on this planet.
And like wings, intelligence has increased in several lineages indepent of one another.
It seems for now, to be the last on the line in the model I roughly created - so it makes sense that it's so valuable in the emergence of intelligence.
We could use a dragster as an analogy. The top fuel dragsters have around 10,000 horsepower. They are very, very impressive. However, this horsepower would not mean squat if there was no way to transfer that energy to the track. That is why dragsters do not use the same tires that a Prius uses.
I think that the evolution of intelligence is like the example above. You can't select for more intelligence unless there is a way for that intelligence to be used, a way to transfer that horsepower to the track. Our hands are definitely a good example of this. They are extremely flexible and allow us to make any tool we want (within reason). We can even see how the wrist and hand morphology changed during human evolution to allow for more flexibility and better manipulation of tools. For example, we can touch the tip of our thumb with the tip of our little finger. Other apes can't do that. This allows us to hold a stick parallel with our forearm, something else that a chimp can not do. It would seem to me that tool use and tool making are very important for evolving an intelligence like ours.
But, just to challenge it a little bit, we could also observe that only two phyla on Earth ever evolved flight. These were also the only two phyla that evolved an articulated skeleton and jointed limbs. But, most things with an articulated skeleton cannot fly.
We can also point out that an articulated skeleton evolved twice. There seems to be a general trend towards this condition for ambulatory terrestrial species.
Since we only have a single example of life evolving it's all we have to go with. The vast majority of life here are unintelligent microbial critters. If we look at land critters most are unintelligent plant life. If we look at flying thingies most are unintelligent insects and microbes.
Is there any reason to think that pattern would not hold true universally?
Absolutely it should hold. I would be stunned if it didn't. Being unintelligent and simple seems to be a very successful evolutionary strategy. Once those niches are filled, however, life will start to branch out to other strategies.